Network Working Group C. Perkins
Internet-Draft Futurewei
Intended status: Standards Track S. Ratliff
Expires: January 4, 2018 Idirect
J. Dowdell
Airbus Defence and Space
L. Steenbrink
HAW Hamburg, Dept. Informatik
V. Mercieca
Airbus Defence and Space
July 3, 2017
Ad Hoc On-demand Distance Vector Version 2 (AODVv2) Routing
draft-perkins-manet-aodvv2-01
Abstract
The Ad Hoc On-demand Distance Vector Version 2 (AODVv2) routing
protocol is intended for use by mobile routers in wireless, multihop
networks. AODVv2 determines unicast routes among AODVv2 routers
within the network in an on-demand fashion.
Status of This Memo
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provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on January 4, 2018.
Copyright Notice
Copyright (c) 2017 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
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Table of Contents
1. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Applicability Statement . . . . . . . . . . . . . . . . . . . 9
4. Data Structures . . . . . . . . . . . . . . . . . . . . . . . 11
4.1. Interface Set . . . . . . . . . . . . . . . . . . . . . . 11
4.2. Router Client Set . . . . . . . . . . . . . . . . . . . . 12
4.3. Neighbor Set . . . . . . . . . . . . . . . . . . . . . . 12
4.4. Sequence Numbers . . . . . . . . . . . . . . . . . . . . 13
4.5. Local Route Set . . . . . . . . . . . . . . . . . . . . . 15
4.6. Multicast Route Message Set . . . . . . . . . . . . . . . 17
4.7. Route Error (RERR) Set . . . . . . . . . . . . . . . . . 18
5. Metrics . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
6. AODVv2 Protocol Operations . . . . . . . . . . . . . . . . . 20
6.1. Initialization . . . . . . . . . . . . . . . . . . . . . 21
6.2. Next Hop Monitoring . . . . . . . . . . . . . . . . . . . 21
6.3. Neighbor Set Update . . . . . . . . . . . . . . . . . . . 23
6.4. Interaction with the Forwarding Plane . . . . . . . . . . 24
6.5. Message Transmission . . . . . . . . . . . . . . . . . . 25
6.6. Route Discovery, Retries and Buffering . . . . . . . . . 26
6.7. Processing Received Route Information . . . . . . . . . . 28
6.7.1. Evaluating Route Information . . . . . . . . . . . . 29
6.7.2. Applying Route Updates . . . . . . . . . . . . . . . 30
6.8. Suppressing Redundant Messages (Multicast Route Message
Set) . . . . . . . . . . . . . . . . . . . . . . . . . . 32
6.9. Suppressing Redundant Route Error Messages (Route Error
Set) . . . . . . . . . . . . . . . . . . . . . . . . . . 35
6.10. Local Route Set Maintenance . . . . . . . . . . . . . . . 35
6.10.1. LocalRoute State Changes . . . . . . . . . . . . . . 36
6.10.2. Reporting Invalid Routes . . . . . . . . . . . . . . 38
7. AODVv2 Protocol Messages . . . . . . . . . . . . . . . . . . 38
7.1. Route Request (RREQ) Message . . . . . . . . . . . . . . 38
7.1.1. RREQ Generation . . . . . . . . . . . . . . . . . . . 40
7.1.2. RREQ Reception . . . . . . . . . . . . . . . . . . . 41
7.1.3. RREQ Forwarding . . . . . . . . . . . . . . . . . . . 42
7.2. Route Reply (RREP) Message . . . . . . . . . . . . . . . 42
7.2.1. RREP Generation . . . . . . . . . . . . . . . . . . . 44
7.2.2. RREP Reception . . . . . . . . . . . . . . . . . . . 45
7.2.3. RREP Forwarding . . . . . . . . . . . . . . . . . . . 47
7.3. Route Reply Acknowledgement (RREP_Ack) Message . . . . . 47
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7.3.1. RREP_Ack Request Generation . . . . . . . . . . . . . 48
7.3.2. RREP_Ack Reception . . . . . . . . . . . . . . . . . 48
7.3.3. RREP_Ack Response Generation . . . . . . . . . . . . 49
7.4. Route Error (RERR) Message . . . . . . . . . . . . . . . 49
7.4.1. RERR Generation . . . . . . . . . . . . . . . . . . . 50
7.4.2. RERR Reception . . . . . . . . . . . . . . . . . . . 52
7.4.3. RERR Regeneration . . . . . . . . . . . . . . . . . . 53
8. RFC 5444 Representation . . . . . . . . . . . . . . . . . . . 54
8.1. Route Request Message Representation . . . . . . . . . . 55
8.1.1. Message Header . . . . . . . . . . . . . . . . . . . 55
8.1.2. Message TLV Block . . . . . . . . . . . . . . . . . . 55
8.1.3. Address Block . . . . . . . . . . . . . . . . . . . . 55
8.1.4. Address Block TLV Block . . . . . . . . . . . . . . . 56
8.2. Route Reply Message Representation . . . . . . . . . . . 56
8.2.1. Message Header . . . . . . . . . . . . . . . . . . . 56
8.2.2. Message TLV Block . . . . . . . . . . . . . . . . . . 57
8.2.3. Address Block . . . . . . . . . . . . . . . . . . . . 57
8.2.4. Address Block TLV Block . . . . . . . . . . . . . . . 57
8.3. Route Reply Acknowledgement Message Representation . . . 58
8.3.1. Message Header . . . . . . . . . . . . . . . . . . . 58
8.3.2. Message TLV Block . . . . . . . . . . . . . . . . . . 58
8.3.3. Address Block . . . . . . . . . . . . . . . . . . . . 58
8.3.4. Address Block TLV Block . . . . . . . . . . . . . . . 58
8.4. Route Error Message Representation . . . . . . . . . . . 58
8.4.1. Message Header . . . . . . . . . . . . . . . . . . . 58
8.4.2. Message TLV Block . . . . . . . . . . . . . . . . . . 59
8.4.3. Address Block . . . . . . . . . . . . . . . . . . . . 59
8.4.4. Address Block TLV Block . . . . . . . . . . . . . . . 59
9. Simple External Network Attachment . . . . . . . . . . . . . 60
10. Precursor Lists . . . . . . . . . . . . . . . . . . . . . . . 62
11. Application of RFC 7182 to AODVv2 . . . . . . . . . . . . . . 63
11.1. RREQ Generation and Reception . . . . . . . . . . . . . 66
11.2. RREP Generation and Reception . . . . . . . . . . . . . 66
11.3. RREP_Ack Generation and Reception . . . . . . . . . . . 67
11.4. RERR Generation and Reception . . . . . . . . . . . . . 68
12. Configuration . . . . . . . . . . . . . . . . . . . . . . . . 68
12.1. Timers . . . . . . . . . . . . . . . . . . . . . . . . . 69
12.2. Protocol Constants . . . . . . . . . . . . . . . . . . . 71
12.3. Local Settings . . . . . . . . . . . . . . . . . . . . . 72
12.4. Network-Wide Settings . . . . . . . . . . . . . . . . . 72
13. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 72
13.1. RFC 5444 Message Type Allocation . . . . . . . . . . . . 73
13.2. RFC 5444 Message TLV Types . . . . . . . . . . . . . . . 73
13.3. RFC 5444 Address Block TLV Type Allocation . . . . . . . 73
13.4. MetricType Allocation . . . . . . . . . . . . . . . . . 74
13.5. ADDRESS_TYPE TLV Values . . . . . . . . . . . . . . . . 74
14. Security Considerations . . . . . . . . . . . . . . . . . . . 75
14.1. Availability . . . . . . . . . . . . . . . . . . . . . . 75
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14.1.1. Denial of Service . . . . . . . . . . . . . . . . . 75
14.1.2. Malicious RERR messages . . . . . . . . . . . . . . 76
14.1.3. False Confirmation of Link Bidirectionality . . . . 77
14.1.4. Message Deletion . . . . . . . . . . . . . . . . . . 78
14.2. Confidentiality . . . . . . . . . . . . . . . . . . . . 78
14.3. Integrity of Routes . . . . . . . . . . . . . . . . . . 78
14.3.1. Message Insertion . . . . . . . . . . . . . . . . . 79
14.3.2. Message Modification - Man in the Middle . . . . . . 79
14.3.3. Replay Attacks . . . . . . . . . . . . . . . . . . . 80
14.4. Protection Mechanisms . . . . . . . . . . . . . . . . . 80
14.4.1. Confidentiality and Authentication . . . . . . . . . 80
14.4.2. Message Integrity using ICVs . . . . . . . . . . . . 80
14.4.3. Replay Protection using Timestamps . . . . . . . . . 81
14.5. Key Management . . . . . . . . . . . . . . . . . . . . . 81
15. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 82
16. References . . . . . . . . . . . . . . . . . . . . . . . . . 83
16.1. Normative References . . . . . . . . . . . . . . . . . . 83
16.2. Informative References . . . . . . . . . . . . . . . . . 83
Appendix A. AODVv2 Draft Updates . . . . . . . . . . . . . . . . 84
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 85
1. Overview
The Ad hoc On-Demand Distance Vector Version 2 (AODVv2) protocol
enables dynamic, multihop routing between participating mobile nodes
wishing to establish and maintain an ad hoc network. The basic
operations of the AODVv2 protocol are route discovery and route
maintenance. AODVv2 does not require nodes to maintain routes to
destinations that are not in active communication. AODVv2 allows
mobile nodes to respond to link breakages and changes in network
topology in a timely manner. The operation of AODVv2 is loop-free,
and by avoiding the Bellman-Ford "counting to infinity" problem
offers quick convergence when the ad hoc network topology changes
(typically, when a node moves in the network). When links break,
AODVv2 causes the affected set of nodes to be notified so that they
are able to invalidate the routes using the lost link.
One distinguishing feature of AODVv2 is its use of a destination
sequence number for each route entry. The destination sequence
number is created by the destination to be included along with any
route information it sends to requesting nodes. Using destination
sequence numbers ensures loop freedom and is simple to program.
Given the choice between two routes to a destination, a requesting
node is required to select the one with the greatest sequence number.
Compared to AODV [RFC3561], AODVv2 has moved some features out of the
scope of the document, notably intermediate route replies, expanding
ring search, and route lifetimes. However, the document has been
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designed to allow their specification in a separate document. Hello
messages and local repair have been removed. AODVv2 provides a
mechanism for the use of multiple metric types. Message formats have
been updated and made compliant with [RFC5444]. AODVv2 control
messages are defined as sets of data, which are mapped to message
elements using the Generalized MANET Packet/Message Format defined in
[RFC5444] and sent using the parameters in [RFC5498]. Verification
of link bidirectionality has been substantially improved, and
additional refinements made for route timeouts and state management.
Finally, multihoming is now supported.
The basic protocol mechanisms are as follows. Since AODVv2 is a
reactive protocol, route discovery is initiated only when a route to
the target is needed (i.e. when a router's client has data to send).
For this purpose, AODVv2 uses Route Request (RREQ) and Route Reply
(RREP) messages as follows: an RREQ is distributed across the
network. When forwarding an RREQ, all routers across the network
also store a possible reverse route back to the originator of the
RREQ. When the target receives the RREQ, it answers with an RREP,
which is then relayed back to the originator along the path stored by
the intermediate routers. A metric value is included within the
messages to indicate the cost of the route. AODVv2 uses sequence
numbers to identify stale routing information, and compares route
metric values to determine if advertised routes could form loops.
Route maintenance includes confirming bidirectionality of links to
next-hop AODVv2 routers, managing route timeouts, using Route Error
(RERR) messages to inform other routers of broken links, and reacting
to received Route Error messages.
The on-demand nature of AODVv2 requires indications to be exchanged
between AODVv2 and the forwarding plane for the following conditions:
o a packet is to be forwarded and route discovery is needed
o packet forwarding fails, in order to report a route error
o packet forwarding succeeds, in order to manage route timeouts.
Security for authentication of AODVv2 routers and encryption of
control messages is accomplished using the TIMESTAMP and ICV TLVs
defined in [RFC7182].
2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
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[RFC2119]. In addition, this document uses terminology from
[RFC5444], and defines the following terms:
AddressList
A list of IP addresses as used in AODVv2 messages.
AckReq
Used in a Route Reply Acknowledgement message to indicate that a
Route Reply Acknowledgement is expected in return.
AdvRte
A route advertised in an incoming route message.
AODVv2 Router
An IP addressable device in the ad hoc network that performs the
AODVv2 protocol operations specified in this document.
CurrentTime
The current time as maintained by the AODVv2 router.
ENAR (External Network Access Router)
An AODVv2 router with an interface to an external, non-AODVv2
network.
Interface Set
The set of all network interfaces supporting AODVv2.
Invalid route
A route that cannot be used for forwarding but still contains
useful sequence number information.
LocalRoute
An entry in the Local Route Set as defined in Section 4.5.
MANET
A Mobile Ad Hoc Network as defined in [RFC2501].
MetricType
The metric type for a metric value included in a message.
MetricTypeList
A list of metric types associated with the addresses in the
AddressList of a Route Error message.
Neighbor
An AODVv2 router from which an RREQ or RREP message has been
received. Neighbors exchange routing information and verify
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bidirectionality of the link to a neighbor before installing a
route via that neighbor into the Local Route Set.
OrigAddr
The source IP address of the IP packet triggering route discovery.
OrigMetric
The metric value associated with the route to OrigPrefix.
OrigPrefix
The prefix configured in the Router Client Set entry which
includes OrigAddr.
OrigPrefixLen
The prefix length, in bits, configured in the Router Client Set
entry which includes OrigAddr.
OrigSeqNum
The sequence number of the AODVv2 router which originated the
Route Request on behalf of OrigAddr.
PktSource
The source address of the IP packet that triggered a Route Error
message.
PrefixLengthList
A list of routing prefix lengths associated with the addresses in
the AddressList of a message.
Reactive
Performed only in reaction to specific events. In AODVv2, routes
are requested only when data packets need to be forwarded. In
this document, "reactive" is synonymous with "on-demand".
RERR (Route Error)
The AODVv2 message type used to indicate that an AODVv2 router
does not have a valid LocalRoute toward one or more destinations.
RERR_Gen (RERR Generating Router)
The AODVv2 router generating a Route Error message.
RerrMsg (RERR Message)
A Route Error (RERR) message.
Routable Unicast IP Address
A unicast IP address that is scoped sufficiently to be forwarded
by a router. Globally-scoped unicast IP addresses and Unique
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Local Addresses (ULAs) [RFC4193] are examples of routable unicast
IP addresses.
Router Client
An address within an address range configured on an AODVv2 router,
on behalf of which that router will initiate and respond to route
discoveries. These addresses may be used by the AODVv2 router
itself or by devices that are reachable without traversing another
AODVv2 router.
RREP (Route Reply)
The AODVv2 message type used to reply to a Route Request message.
RREP_Gen (RREP Generating Router)
The AODVv2 router that generates the Route Reply message, i.e.,
the router configured with TargAddr as a Router Client.
RREQ (Route Request)
The AODVv2 message type used to discover a route to TargAddr and
distribute information about a route to OrigPrefix.
RREQ_Gen (RREQ Generating Router)
The AODVv2 router that generates the Route Request message, i.e.,
the router configured with OrigAddr as a Router Client.
RteMsg (Route Message)
A Route Request (RREQ) or Route Reply (RREP) message.
SeqNum
The sequence number maintained by an AODVv2 router to indicate
freshness of route information.
SeqNumList
A list of sequence numbers associated with the addresses in the
AddressList of a message.
TargAddr
The target address of a route request, i.e., the destination
address of the IP packet triggering route discovery.
TargMetric
The metric value associated with the route to TargPrefix.
TargPrefix
The prefix configured in the Router Client Set entry which
includes TargAddr.
TargPrefixLen
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The prefix length, in bits, configured in the Router Client Set
entry which includes TargAddr.
TargSeqNum
The sequence number of the AODVv2 router which originated the
Route Reply on behalf of TargAddr.
Unreachable Address
An address reported in a Route Error message, as described in
Section 7.4.1.
Upstream
In the direction from destination to source (from TargAddr to
OrigAddr).
Valid route
A route that can be used for forwarding.
This document uses the notational conventions in Table 1 to simplify
the text.
+-----------------------+------------------------------------+
| Notation | Meaning |
+-----------------------+------------------------------------+
| Route[Address] | A route toward Address |
| Route[Address].Field | A field in a route toward Address |
| RteMsg.Field | A field in either RREQ or RREP |
| RerrMsg.Field | A field in a RERR |
+-----------------------+------------------------------------+
Table 1: Notational Conventions
3. Applicability Statement
The AODVv2 routing protocol is a reactive routing protocol designed
for use in mobile ad hoc wireless networks, and may also be useful in
networks where the nodes are not mobile but economical route
maintenance is still required. A reactive protocol only sends
messages to discover a route when there is data to send on that
route. This requires an interaction with the forwarding plane, to
indicate when a packet is to be forwarded, in case reactive route
discovery is needed. The set of signals exchanged between AODVv2 and
the forwarding plane are discussed in Section 6.4.
AODVv2 is designed for stub or disconnected mobile ad hoc networks,
i.e., non-transit networks or those not connected to the internet.
AODVv2 routers can, however, be configured to perform gateway
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functions when attached to external networks, as discussed in
Section 9.
AODVv2 handles a wide variety of mobility and traffic patterns by
determining routes on-demand. In networks with a large number of
routers, AODVv2 is best suited for relatively sparse traffic
scenarios where each router forwards IP packets to a small percentage
of destination addresses in the network. In such cases fewer routes
are needed, and far less control traffic is produced. In large
networks with dense traffic patterns, AODVv2 control messages may
cause a broadcast storm, overwhelming the network with control
messages. The transmission priorities described in Section 6.5
prioritize route maintenance traffic over route discovery traffic.
Data packets may be buffered until a route to their destination is
available, as described in Section 6.6.
AODVv2 is well suited to reactive scenarios such as emergency and
disaster relief, where the ability to communicate might be more
important than being assured of secure operations. For many other ad
hoc networking applications, in which insecure operation could negate
the value of establishing communication paths, it is important for
neighboring AODVv2 routers to establish security associations with
one another.
AODVv2 provides for message integrity and security against replay
attacks by using integrity check values, timestamps and sequence
numbers, as described in Section 14. When security associations have
been established, encryption can be used for AODVv2 messages to
ensure that only trusted routers participate in routing operations.
The AODVv2 route discovery process aims for a route to be established
in both directions along the same path. Uni-directional links are
not suitable; AODVv2 will detect and exclude those links from route
discovery. The route discovered is optimized for the requesting
router, and the return path may not be the optimal route.
AODVv2 is applicable to memory constrained devices, since only a
little routing state is maintained in each AODVv2 router. AODVv2
routes that are not needed for forwarding data do not need to be
maintained.
AODVv2 supports routers with multiple interfaces and multiple IP
addresses per interface. A router may also use the same IP address
on multiple interfaces. AODVv2 requires only that each interface
configured for AODVv2 has at least one unicast IP address. Address
assignment procedures are out of scope for AODVv2.
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AODVv2 supports Router Clients with multiple interfaces, as long as
each interface is configured with its own unicast IP address.
The routing algorithm in AODVv2 has been operated at layers other
than the network layer, using layer-appropriate addresses.
AODVv2 is based on AODV [RFC3561]. The following important protocol
mechanisms have changed:
o Bidirectionality is ensured using a new mechanism
o Alternate metrics may be used to determine route quality
o Support for multiple interfaces has been improved
o Support for multi-interface IP addresses has been added
o A new security model allowing end to end integrity checks has been
added
o A new message format ([RFC5444]) is used.
4. Data Structures
4.1. Interface Set
The Interface Set is a conceptual data structure which contains
information about all interfaces configured for use by AODVv2. Any
interface with an IP address can be used. Multiple interfaces on a
single router can be used. Multiple interfaces on the same router
may be configured with the same IP address.
Each member in the Interface Set MUST contain the following:
Interface.Id
An identifier that is unique in node-local scope, allowing the
AODVv2 implementation to identify exactly one local network
interface.
If multiple interfaces of the AODVv2 router are configured for use by
AODVv2, they MUST be configured in the Interface Set.
Implementations using only one interface do not need the Interface
Set, since their single interface is already uniquely identifiable.
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4.2. Router Client Set
An AODVv2 router discovers routes for its own local applications and
also for its Router Clients that are reachable without traversing
another AODVv2 router. The addresses used by these devices, and the
AODVv2 router itself, are configured in the Router Client Set. An
AODVv2 router will only originate Route Request and Route Reply
messages on behalf of its configured Router Client addresses.
Router Client Set entries contain:
RouterClient.IPAddress
An IP address or the start of an address range that requires route
discovery services from the AODVv2 router.
RouterClient.PrefixLength
The length, in bits, of the routing prefix associated with the
RouterClient.IPAddress. If the prefix length is not equal to the
address length of RouterClient.IPAddress, the AODVv2 router MUST
participate in route discovery on behalf of all addresses within
that prefix.
RouterClient.Cost
The cost associated with reaching this address or address range.
4.3. Neighbor Set
A Neighbor Set MUST be maintained with information about neighboring
AODVv2 routers. Neighbor Set entries are stored when AODVv2 messages
are received. If the Neighbor is chosen as a next hop on an
installed route, the link to the Neighbor MUST be verified to be
bidirectional and the result stored in this set. A route is not
valid until the link is confirmed to be bidirectional.
Neighbor Set entries MUST contain:
Neighbor.IPAddress
An IP address of the neighboring router.
Neighbor.State
Indicates whether the link to the neighbor is bidirectional.
There are three possible states: Confirmed, Heard, and
Blacklisted. Heard is the initial state. Confirmed indicates
that the link to the neighbor has been confirmed as bidirectional.
Blacklisted indicates that the link to the neighbor is being
treated as uni-directional. Section 6.2 discusses how to monitor
link bidirectionality.
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Neighbor.Timeout
Indicates the time at which the Neighbor.State should be updated:
o If the value of Neighbor.State is Blacklisted, this indicates the
time at which Neighbor.State will revert to Heard. This value is
calculated at the time the router is blacklisted and by default is
equal to CurrentTime + MAX_BLACKLIST_TIME.
o If Neighbor.State is Heard, and an RREP_Ack has been requested
from the neighbor, it indicates the time at which Neighbor.State
will be set to Blacklisted, if an RREP_Ack has not been received.
o If the value of Neighbor.State is Heard and no RREP_Ack has been
requested, or if Neighbor.State is Confirmed, this time is set to
INFINITY_TIME.
Neighbor.Interface
The interface on which the link to the neighbor was established.
Neighbor.AckSeqNum
The next sequence number to use for the TIMESTAMP value in an
RREP_Ack request, in order to detect replay of an RREP_Ack
response. AckSeqNum is initialized to a random value.
Neighbor.HeardRERRSeqNum
The last heard sequence number used as the TIMESTAMP value in a
RERR received from this neighbor, saved in order to detect replay
of a RERR message. HeardRERRSeqNum is initialized to zero.
See Section 11.3 and Section 11.4 for more information on how
Neighbor.AckSeqNum and Neighbor.HeardRERRSeqNum are used.
4.4. Sequence Numbers
Sequence Numbers enable AODVv2 routers to determine the temporal
order of route discovery messages that originate from a AODVv2
router, and thus to identify stale routing information so that it can
be discarded. The sequence number fulfills the same roles as the
"Destination Sequence Number" of DSDV [Perkins94], and the AODV
Sequence Number in [RFC3561]. The sequence numbers from two
different routers are not comparable; route discovery messages with
sequence numbers belonging to two different routers cannot be
compared to determine temporal ordering.
Each AODVv2 router in the network MUST maintain its own sequence
number. All RREQ and RREP messages created by an AODVv2 router
include the router's sequence number, reported as a 16-bit unsigned
integer. Each AODVv2 router MUST ensure that its sequence number is
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strictly increasing, and that it is incremented by one (1) whenever
an RREQ or RREP is created, except when the sequence number is 65,535
(the maximum value of a 16-bit unsigned integer), in which case it
MUST be reset to one (1) to achieve wrap around. The value zero (0)
is reserved to indicate that the router's sequence number is unknown.
An AODVv2 router MUST use its sequence number only on behalf of its
configured Router Clients; route messages forwarded by other routers
retain the originator's sequence number.
To determine if newly received information is stale and therefore
redundant compared to other information originated by the same
router, the sequence number attached to the information is compared
to the sequence number of existing information about the same route.
The comparison is carried out by subtracting the existing sequence
number from the newly received sequence number, using unsigned
arithmetic. The result of the subtraction is to be interpreted as a
signed 16-bit integer.
o If the result is negative, the newly received information is
considered older than the existing information and therefore stale
and redundant and MUST therefore be discarded.
o If the result is positive, the newly received information is newer
than the existing information and is not considered stale or
redundant and MUST therefore be processed.
o If the result is zero, the newly received information is not
considered stale, and therefore MUST be processed further in case
the new information offers a better route (see Section 6.7.1 and
Section 6.8).
Along with the algorithm in Section 6.7.1, maintaining temporal
ordering ensures loop freedom.
An AODVv2 router SHOULD maintain its sequence number in persistent
storage. On routers unable to store persistent AODVv2 state,
recovery can impose a performance penalty (e.g., in case of AODVv2
router reboot), since if a router loses its sequence number, there is
a delay (by default, on the order of minutes) before the router can
resume full operations. If the sequence number is lost, the router
MUST follow the procedure in Section 6.1 to safely resume routing
operations with a new sequence number.
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4.5. Local Route Set
All AODVv2 routers MUST maintain a Local Route Set, containing
information obtained from AODVv2 route messages. The Local Route Set
is considered to be stored separately from the forwarding plane's
routing table (referred to as Routing Information Base (RIB)), which
may be updated by other routing protocols operating on the AODVv2
router as well. The Routing Information Base is updated using
information from the Local Route Set. Alternatively, if the
information specified below can be added to RIB entries,
implementations MAY choose to modify the Routing Information Base
directly instead of maintaining a dedicated Local Route Set.
Routes obtained from AODVv2 route messages are referred to in this
document as LocalRoutes, and MUST contain the following information:
LocalRoute.Address
An address, which, when combined with LocalRoute.PrefixLength,
describes the set of destination addresses for which this route
enables forwarding.
LocalRoute.PrefixLength
The prefix length, in bits, associated with LocalRoute.Address.
LocalRoute.SeqNum
The sequence number associated with LocalRoute.Address, obtained
from the last route message that successfully updated this entry.
LocalRoute.NextHop
The source IP address of the IP packet containing the AODVv2
message advertising the route to LocalRoute.Address, i.e., an IP
address of the AODVv2 router used for the next hop on the path
toward LocalRoute.Address.
LocalRoute.NextHopInterface
The interface used to send IP packets toward LocalRoute.Address.
LocalRoute.LastUsed
If this route is installed in the Routing Information Base, the
time it was last used to forward an IP packet. If not, the time
at which the LocalRoute was created.
LocalRoute.LastSeqNumUpdate
The time LocalRoute.SeqNum was last updated.
LocalRoute.MetricType
The type of metric associated with this route. See Section 5 for
information about AODVv2's handling of multiple metric types.
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LocalRoute.Metric
The cost of the route toward LocalRoute.Address expressed in units
consistent with LocalRoute.MetricType.
LocalRoute.Precursors (optional feature)
A list of upstream neighbors using the route (see Section 10).
LocalRoute.SeqNoRtr
If nonzero, the IP address of the router that originated the
Sequence Number for this route.
LocalRoute.State
The last known state (Unconfirmed, Idle, Active, or Invalid) of
the route.
There are four possible states for a LocalRoute:
Unconfirmed
A route obtained from a Route Request message, which has not yet
been confirmed as bidirectional. It MUST NOT be stored in the RIB
to forward general data-plane traffic, but it can be used to
transmit RREP packets along with a request for bidirectional link
verification. An Unconfirmed route is not otherwise considered a
valid route. This state is only used for routes obtained through
RREQ messages.
Idle
A route that has been confirmed to be bidirectional, but has not
been used in the last ACTIVE_INTERVAL. It can be used for
forwarding IP packets, and therefore it is considered a valid
route.
Active
A valid route that has been used for forwarding IP packets during
the last ACTIVE_INTERVAL.
Invalid
A route that has expired or has broken. It MUST NOT be used for
forwarding IP packets. Invalid routes contain the destination's
sequence number, which may be useful when assessing freshness of
incoming routing information.
If the Local Route Set is stored separately from the RIB, routes are
added to the RIB when LocalRoute.State becomes Active, and removed
from the RIB when LocalRoute.State becomes Invalid. Changes to
LocalRoute state are detailed in Section 6.10.1.
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4.6. Multicast Route Message Set
Multicast Route Request (RREQ) messages can be tested for redundancy
to avoid unnecessary processing and forwarding.
The Multicast Route Message Set is a conceptual set which contains
information about previously received multicast route messages, so
that incoming route messages can be compared with previously received
messages to determine if the incoming information is redundant or
stale, so that the router can avoid sending redundant control
traffic.
Multicast Route Message Set entries contain the following
information:
RteMsg.OrigPrefix
The prefix associated with OrigAddr, the source address of the IP
packet triggering the route request.
RteMsg.OrigPrefixLen
The prefix length associated with RteMsg.OrigPrefix, originally
from the Router Client Set entry on RREQ_Gen which includes
OrigAddr.
RteMsg.TargPrefix
The prefix associated with TargAddr, the destination address of
the IP packet triggering the route request. In an RREQ this MUST
be set to TargAddr.
RteMsg.OrigSeqNum
The sequence number associated with the route to OrigPrefix, if
RteMsg is an RREQ.
RteMsg.TargSeqNum
The sequence number associated with the route to TargPrefix.
RteMsg.MetricType
The metric type of the route requested.
RteMsg.Metric
The metric value received in the RteMsg.
RteMsg.Timestamp
The last time this Multicast Route Message Set entry was updated.
RteMsg.RemovalTime
The time at which this entry MUST be removed from the Multicast
Route Message Set.
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RteMsg.Interface
The interface on which the message was received.
RteMsg.SeqNoRtr
If nonzero, the IP address of the router that originated the
Sequence Number for this route.
The Multicast Route Message Set is maintained so that no two entries
have the same OrigPrefix, OrigPrefixLen, TargPrefix, and MetricType.
See Section 6.8 for details about updating this set.
4.7. Route Error (RERR) Set
Each RERR message sent because no route exists for packet forwarding
SHOULD be recorded in a conceptual set called the Route Error (RERR)
Set. Each entry contains the following information:
RerrMsg.Timeout
The time after which the entry SHOULD be deleted.
RerrMsg.UnreachableAddress
The UnreachableAddress reported in the AddressList of the RERR.
RerrMsg.PktSource:
The PktSource of the RERR.
See Section 6.9 for instructions on how to update the set.
5. Metrics
Metrics measure a cost or quality associated with a route or a link,
e.g., latency, delay, financial cost, energy, etc. Metric values are
reported in Route Request and Route Reply messages.
In Route Request messages, the metric describes the cost of the route
from OrigPrefix to the router transmitting the Route Request. For
RREQ_Gen, this is the cost associated with the Router Client Set
entry which includes OrigAddr. For routers which forward the RREQ,
this is the cost from OrigPrefix to the forwarding router, combining
the metric value from the received RREQ message with knowledge of the
link cost from the sender to the receiver, i.e., the incoming link
cost. This updated route cost is included when forwarding the Route
Request message, and used to install a route to OrigPrefix.
Similarly, in Route Reply messages, the metric reflects the cost of
the route from TargPrefix to the router transmitting the Route Reply.
For RREP_Gen, this is the cost associated with the Router Client Set
entry which includes TargAddr. For routers which forward the RREP,
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this is the cost from TargPrefix to the forwarding router, combining
the metric value from the received RREP message with knowledge of the
link cost from the sender to the receiver, i.e., the incoming link
cost. This updated route cost is included when forwarding the Route
Reply message, and used to install a route to TargPrefix.
When link metrics are symmetric, the cost of the routes installed in
the Local Route Set at each router will be correct. This assumption
is often inexact, but calculating incoming/outgoing metric data is
outside of scope of this document. The route discovered is good for
the requesting router, but the return path may not be the optimal
route.
AODVv2 enables the use of multiple metric types. Each route
discovery attempt indicates the metric type which is requested for
the route. Multiple valid routes may exist in the Local Route Set
for the same address and prefix length but for different metric
types. More than one route to a particular address and prefix length
MUST NOT exist in the Routing Information Base unless each packet can
be inspected to determine which route in the RIB has the proper
metric type as required for that packet. Otherwise, only one route
at a time to a particular address and prefix length may exist in the
RIB. The algorithm used to inspect the packet and make the
determination about which the routes should be installed in the
Routing Information Base is outside the scope of AODVv2.
For each MetricType, AODVv2 requires:
o A MetricType number, to indicate the metric type of a route.
Currently allocated MetricType numbers are listed in Section 13.4.
o A maximum value, denoted MAX_METRIC[MetricType]. This MUST always
be the maximum expressible metric value of type MetricType. Field
lengths associated with metric values are found in Section 13.4.
If the cost of a route exceeds MAX_METRIC[MetricType], the route
cannot be stored and is ignored.
o A function for incoming link cost, denoted Cost(L). Using
incoming link costs means that the route obtained has a metric
accurate for the direction back towards the originating router.
o A function for route cost, denoted Cost(R).
o A function to analyze routes for potential loops based on metric
information, denoted LoopFree(R1, R2). LoopFree verifies that a
route R2 is not a sub-section of another route R1. An AODVv2
router invokes LoopFree() as part of the process in Section 6.7.1,
when an advertised route (R1) and an existing LocalRoute (R2) have
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the same destination address, metric type, and sequence number.
LoopFree returns FALSE to indicate that an advertised route is not
to be used to update a stored LocalRoute, as it may cause a
routing loop. In the case where the existing LocalRoute is
Invalid, it is possible that the advertised route includes the
existing LocalRoute and came from a router which did not yet
receive notification of the route becoming Invalid, so the
advertised route should not be used to update the Local Route Set,
in case it forms a loop to a broken route.
AODVv2 currently supports cost metrics where Cost(R) is strictly
increasing, by defining:
o Cost(R) := Sum of Cost(L) of each link in the route
o LoopFree(R1, R2) := ( Cost(R1) <= Cost(R2) )
Implementers MAY consider metric types that are not strictly
increasing, but the definitions of Cost and LoopFree functions for
such types are undefined, and interoperability issues need to be
considered.
6. AODVv2 Protocol Operations
AODVv2 protocol operations include:
o managing sequence numbers,
o monitoring next hop AODVv2 routers on discovered routes and
updating the Neighbor Set,
o performing route discovery and dealing with requests from other
routers,
o processing incoming route information and updating the Local Route
Set,
o updating the Multicast Route Message Set and suppressing redundant
messages, and
o reporting broken routes.
These processes are discussed in detail in the following sections.
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6.1. Initialization
When an AODVv2 router does not have information about its previous
sequence number, or if its sequence number is lost at any point, the
router reinitializes its sequence number to one (1). However, other
AODVv2 routers may still hold sequence number information that this
router previously issued. Since sequence number information is
removed if there has been no update to the sequence number in
MAX_SEQNUM_LIFETIME, the initializing router MUST wait for
MAX_SEQNUM_LIFETIME before it creates any messages containing its new
sequence number.
During this wait period, the router is permitted to do the following:
o Process information in a received RREQ or RREP message to obtain a
route to the originator or target of that route discovery
o Forward a received RREQ or RREP
o Send an RREP_Ack
o Maintain valid routes in the Local Route Set
o Create, process and forward RERR messages
6.2. Next Hop Monitoring
To ensure AODVv2 routers do not establish routes over uni-directional
links, AODVv2 routers MUST verify that the link to the next hop
router is bidirectional before marking a route as valid in the Local
Route Set.
AODVv2 provides a mechanism for testing bidirectional connectivity
during route discovery, and blacklisting routers where bidirectional
connectivity is not available. If a route discovery is retried by
RREQ_Gen, the blacklisted routers are excluded from the process, and
a different route can be discovered. Further, a route is not to be
used for forwarding until the bidirectionality of the link to the
next hop is confirmed. AODVv2 routers do not need to monitor
bidirectionality for links to neighboring routers which are not used
as next hops on routes in the Local Route Set.
o Bidirectional connectivity to upstream routers is tested as
necessary by requesting acknowledgement of RREP messages,
including an AckReq element to indicate that an acknowledgement is
requested. This MUST be answered by sending an RREP_Ack in
response. Receipt of an RREP_Ack within RREP_Ack_SENT_TIMEOUT
demonstrates that bidirectional connectivity exists. Otherwise,
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the link is considered to be unidirectional. All AODVv2 routers
MUST support this process, which is explained in Section 7.2 and
Section 7.3.
o Receipt of an RREP message containing the route to TargAddr
confirms bidirectionality to the downstream router, since an RREP
message is a reply to an RREQ message which previously crossed the
link in the opposite direction.
To assist with next hop monitoring, a Neighbor Set (Section 4.3) is
maintained. When an RREQ or RREP is received, an AODVv2 router
searches for an entry in the Neighbor Set where all of the following
conditions are met:
o Neighbor.IPAddress == IP address from which the RREQ or RREP was
received
o Neighbor.Interface == Interface on which the RREQ or RREP was
received.
If no such entry exists, a new entry is created as described in
Section 6.3. While the value of Neighbor.State is Heard,
acknowledgement of RREP messages sent to that neighbor MUST be
requested. If an acknowledgement is not received within the timeout
period, the neighbor MUST have Neighbor.State set to Blacklisted. If
an acknowledgement is received within the timeout period,
Neighbor.State is set to Confirmed. When the value of Neighbor.State
is Confirmed, the request for an acknowledgement of any other RREP
message is unnecessary.
Additional indications of connectivity may be available from other
operations, for example:
o MAC layer protocol assuring bidirectional links
o Route timeout
o Lower layer triggers, e.g. message reception or link status
notifications
o TCP timeouts
o Promiscuous listening
o receipt of a Neighborhood Discovery Protocol HELLO message with
the receiving router listed as a neighbor [RFC6130]
o Other monitoring mechanisms or heuristics
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If such an external process signals that the link to a neighbor is
bidirectional, the AODVv2 router MAY update the matching Neighbor Set
entry by changing the value of Neighbor.State to Confirmed. If an
external process signals that a link is not bidirectional, the the
value of Neighbor.State MAY be changed to Blacklisted.
6.3. Neighbor Set Update
On receipt of an RREQ or RREP message, the Neighbor Set MUST be
checked for an entry with Neighbor.IPAddress which matches the source
IP address of a packet containing the AODVv2 message. If no matching
entry is found, a new entry is created.
A new Neighbor Set entry is created as follows:
o Neighbor.IPAddress := Source IP address of the received route
message
o Neighbor.State := Heard
o Neighbor.Timeout := INFINITY_TIME
o Neighbor.Interface := Interface on which the RREQ or RREP was
received. (see Section 4.1).
When an RREP_Ack request is sent to a neighbor, the Neighbor Set
entry is updated as follows:
o Neighbor.Timeout := CurrentTime + RREP_Ack_SENT_TIMEOUT
When a received message is one of the following:
o an RREP which answers an RREQ sent within RREQ_WAIT_TIME over the
same interface as Neighbor.Interface
o an RREP_Ack response received from a Neighbor with Neighbor.State
set to Heard, where Neighbor.Timeout > CurrentTime
then the link to the neighbor is bidirectional and the Neighbor Set
entry is updated as follows:
o Neighbor.State := Confirmed
o Neighbor.Timeout := INFINITY_TIME
When the Neighbor.Timeout is reached and Neighbor.State is Heard,
then an RREP_Ack response has not been received from the neighbor
within RREP_Ack_SENT_TIMEOUT of sending the RREP_Ack request. The
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link is considered to be uni-directional and the Neighbor Set entry
is updated as follows:
o Neighbor.State := Blacklisted
o Neighbor.Timeout := CurrentTime + MAX_BLACKLIST_TIME
When the Neighbor.Timeout is reached and Neighbor.State is
Blacklisted, the Neighbor Set entry is updated as follows:
o Neighbor.State := Heard
If an external mechanism reports a link as broken, the Neighbor Set
entry SHOULD be removed.
Route requests (RREQs) from neighbors with Neighbor.State set to
Blacklisted MUST be ignored, to avoid persistent IP packet loss or
protocol failures. Neighbor.Timeout allows the neighbor to again be
allowed to participate in route discoveries after MAX_BLACKLIST_TIME,
in case the link between the routers has become bidirectional.
6.4. Interaction with the Forwarding Plane
The signals described in the following are conceptual in nature, and
can be implemented in various ways. Conformant implementations of
AODVv2 are not mandated to implement the forwarding plane separately
from the control plane or data plane; these signals and interactions
are identified simply as assistance for implementers who may find
them useful.
AODVv2 requires signals from the forwarding plane:
o A packet cannot be forwarded because a route is unavailable:
AODVv2 needs to know the source and destination IP addresses of
the packet. If the source of the packet is configured as a Router
Client, the router SHOULD initiate route discovery to the
destination. If it is not a Router Client, the router SHOULD
create a Route Error message.
o A packet is to be forwarded: AODVv2 needs to check the state of
the route to ensure it is still valid.
o Packet forwarding succeeds: AODVv2 needs to update the record of
when a route was last used to forward a packet.
o Packet forwarding failure occurs: AODVv2 needs to create a Route
Error message.
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AODVv2 needs to send signals to the forwarding plane when:
o A route discovery is in progress: buffering might be configured
for packets requiring a route, while route discovery is attempted.
o A route discovery failed: any buffered packets requiring that
route should be discarded, and the source of the packet should be
notified that the destination is unreachable (using an ICMP
Destination Unreachable message). Route discovery fails if an
RREQ cannot be generated because the control message generation
limit has been reached (seeSection 6.5), or if an RREP is not
received within RREQ_WAIT_TIME (see Section 6.6).
o A route discovery succeeded: install a corresponding route into
the Routing Information Base and begin transmitting any buffered
packets.
o A route has been made invalid: remove the corresponding route from
the Routing Information Base.
o A route has been updated: update the corresponding route in the
Routing Information Base.
o If routes with more than one metric type are available to a
destination, a way to identify the route that is allowable for the
metric type associated with forwarding the incoming packet.
6.5. Message Transmission
AODVv2 sends [RFC5444] formatted messages using the parameters for
port number and IP protocol specified in [RFC5498]. Mapping of
AODVv2 data to [RFC5444] messages is detailed in Section 8. AODVv2
multicast messages are sent to the link-local multicast address LL-
MANET-Routers [RFC5498]. All AODVv2 routers MUST subscribe to LL-
MANET-Routers on all AODVv2 interfaces [RFC5498] to receive AODVv2
messages. Note that multicast messages MAY be sent via unicast. For
example, this may occur for certain link-types (non-broadcast media),
for manually configured router adjacencies, or in order to improve
robustness.
When multiple interfaces are available, an AODVv2 router transmitting
a multicast message to LL-MANET-Routers MUST send the message on all
interfaces that have been configured for AODVv2 operation, as given
in the Interface Set (Section 4.1).
To avoid congestion, each AODVv2 router's rate of message generation
SHOULD be administratively configurable and rate-limited
(CONTROL_TRAFFIC_LIMIT). Messages SHOULD NOT be sent more frequently
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than one message per (1 / CONTROL_TRAFFIC_LIMIT)th of a second. If
this threshold is reached, messages MUST be sent based on their
priority:
o Highest priority SHOULD be given to RREP_Ack messages. This
allows links between routers to be confirmed as bidirectional and
avoids undesired blacklisting of next hop routers.
o Second priority SHOULD be given to RERR messages for undeliverable
IP packets. This avoids repeated forwarding of packets over
broken routes that are still in use by other routers.
o Third priority SHOULD be given to RREP messages in order that
RREQs do not time out.
o Fourth priority SHOULD be given to RREQ messages.
o Fifth priority SHOULD be given to RERR messages for newly
invalidated routes.
o Lowest priority SHOULD be given to RERR messages generated in
response to RREP messages which cannot be forwarded. In this case
the route request will be retried at a later point.
To implement the congestion control, a queue length is set. If the
queue is full, in order to queue a new message, a message of lower
priority must be removed from the queue. If this is not possible,
the new message MUST be discarded. The queue should be sorted in
order of message priority
6.6. Route Discovery, Retries and Buffering
AODVv2's RREQ and RREP messages are used for route discovery. RREQ
messages are multicast to solicit an RREP, whereas RREP are unicast.
The constants used in this section are defined in Section 12.
When an AODVv2 router needs to forward an IP packet (with source
address OrigAddr and destination address TargAddr) from one of its
Router Clients, it needs a route to TargAddr in its Routing
Information Base. If no route exists, the AODVv2 router generates
(RREQ_Gen) and multicasts a Route Request message (RREQ), on all
configured interfaces, containing information about the source and
destination. The procedure for this is described in Section 7.1.1.
Each generated RREQ results in an increment to the router's sequence
number. The AODVv2 router generating an RREQ is referred to as
RREQ_Gen.
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Buffering might be configured for IP packets awaiting a route for
forwarding by RREQ_Gen, if sufficient memory is available. Buffering
of IP packets might have both positive and negative effects. TCP
connection establishment will benefit if packets are queued while
route discovery is performed [Koodli01], but real-time traffic,
voice, and scheduled delivery may suffer if packets are buffered and
subjected to delays. Recommendations for appropriate buffer methods
are out of scope for this specification. Determining which packets
to discard first when the buffer is full is a matter of policy at
each AODVv2 router. Using different (or no) buffer methods might
affect performance but does not affect interoperability.
RREQ_Gen awaits reception of a Route Reply message (RREP) containing
a route toward TargAddr. This can be achieved by monitoring the
entry in the Multicast Route Message Table that corresponds to the
generated RREQ. When CurrentTime exceeds RteMsg.Timestamp +
RREQ_WAIT_TIME and no RREP has been received, RREQ_Gen will retry the
route discovery.
To reduce congestion in a network, repeated attempts at route
discovery for a particular target address utilize a binary
exponential backoff: for each additional attempt, the time to wait
for receipt of the RREP is multiplied by 2. If the requested route
is not discovered within the wait period, another RREQ is sent, up to
a total of DISCOVERY_ATTEMPTS_MAX. This is the same technique used
in AODV [RFC3561].
Through the use of bidirectional link monitoring and blacklists (see
Section 6.2), uni-directional links on an initially selected route
will be ignored on subsequent route discovery attempts.
After DISCOVERY_ATTEMPTS_MAX and the corresponding wait time for an
RREP response to the final RREQ, route discovery is considered to
have failed. If an attempted route discovery has failed, RREQ_Gen
SHOULD wait at least RREQ_HOLDDOWN_TIME before attempting another
route discovery to the same destination, in order to avoid repeatedly
generating control traffic that is unlikely to discover a route. Any
IP packets buffered for TargAddr are also dropped and a Destination
Unreachable ICMP message (Type 3) with a code of 1 (Host Unreachable
Error) is delivered to the source of the packet, so that the
application knows about the failure.
If RREQ_Gen does receive a route message containing a route to
TargAddr within the timeout, it processes the message according to
Section 7. When a valid LocalRoute entry is created in the Local
Route Set, the route is also installed in the Routing Information
Base, and the router will begin sending the buffered IP packets. Any
retry timers for the corresponding RREQ are then cancelled.
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During route discovery, all routers on the path obtain a route to
both OrigPrefix and TargPrefix, so that routes are constructed in
both directions. The route is optimized for the forward route.
6.7. Processing Received Route Information
A Route Request (RREQ) contains a route to OrigPrefix, and a Route
Reply (RREP) contains a route to TargPrefix. All AODVv2 routers that
receive a route message are able to store the route contained within
it in their Local Route Set. Incoming information is first checked to
verify that it is both safe to use and offers an improvement to
existing information, as explained in Section 6.7.1. If these checks
pass, the Local Route Set MUST be updated according to Section 6.7.2.
In the processes below, RteMsg is used to denote the received route
message, AdvRte is used to denote the route contained within it, and
LocalRoute denotes an existing entry in the Local Route Set which
matches AdvRte on address, prefix length, metric type, and SeqNoRtr.
AdvRte has the following properties:
o AdvRte.Address := RteMsg.OrigPrefix (in RREQ) or RteMsg.TargPrefix
(in RREP)
o AdvRte.PrefixLength := RteMsg.OrigPrefixLen (in RREQ) or
RteMsg.TargPrefixLen (in RREP). If no prefix length was included
in RteMsg, prefix length is the address length, in bits, of
RteMsg.OrigPrefix (in RREQ) or RteMsg.TargPrefix (in RREP)
o AdvRte.SeqNum := RteMsg.OrigSeqNum (in RREQ) or RteMsg.TargSeqNum
(in RREP)
o AdvRte.NextHop := RteMsg.IPSourceAddress (an address of the
sending interface of the router from which the RteMsg was
received)
o AdvRte.MetricType := RteMsg.MetricType
o AdvRte.Metric := RteMsg.Metric
o AdvRte.Cost := Cost(R) using the cost function associated with the
route's metric type. For cost metrics, Cost(R) = AdvRte.Metric +
Cost(L), as described in Section 5, where L is the link from the
advertising router
o AdvRte.SeqNoRtr := the IP address in the Address List of type
SeqNoRtr if one exists, otherwise 0
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6.7.1. Evaluating Route Information
An incoming advertised route (AdvRte) is compared to existing
LocalRoutes to determine whether the advertised route is to be used
to update the AODVv2 Local Route Set. The incoming route information
MUST be processed as follows:
1. Search for LocalRoutes in the Local Route Set matching AdvRte's
address, prefix length, metric type, and SeqNoRtr (the AODVv2
router address corresponding to the sequence number).
* If no matching LocalRoute exists, AdvRte MUST be used to
update the Local Route Set and no further checks are required.
* If matching LocalRoutes are found, continue to the next step.
2. Compare sequence numbers using the technique described in
Section 4.4
* If AdvRte is more recent than all matching LocalRoutes, AdvRte
MUST be used to update the Local Route Set and no further
checks are required.
* If AdvRte is stale, AdvRte MUST NOT be used to update the
Local Route Set. Ignore AdvRte for further processing.
* If the sequence numbers are equal, continue to the next step.
3. Check that AdvRte is safe against routing loops compared to all
matching LocalRoutes (see Section 5)
* If LoopFree(AdvRte, LocalRoute) returns FALSE, ignore AdvRte
for further processing. AdvRte MUST NOT be used to update the
Local Route Set because using the incoming information might
cause a routing loop.
* If LoopFree(AdvRte, LocalRoute) returns TRUE, continue to the
next step.
4. Compare route costs
* If AdvRte is better than all matching LocalRoutes, it MUST be
used to update the Local Route Set because it offers
improvement.
* If AdvRte is equal in cost and LocalRoute is valid, AdvRte
SHOULD NOT be used to update the Local Route Set because it
will offer no improvement.
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* If AdvRte is worse and LocalRoute is valid, ignore AdvRte for
further processing. AdvRte MUST NOT be used to update the
Local Route Set because it does not offer any improvement.
* If AdvRte is not better (i.e., it is worse or equal) but
LocalRoute is Invalid, AdvRte SHOULD be used to update the
Local Route Set because it can safely repair the existing
Invalid LocalRoute.
If the advertised route is to be used to update the Local Route Set,
the procedure in Section 6.7.2 MUST be followed. If not, non-optimal
routes will remain in the Local Route Set.
For information on how to apply these changes to the Routing
Information Base, see Section 4.5.
6.7.2. Applying Route Updates
After determining that AdvRte is to be used to update the Local Route
Set (as described in Section 6.7.1), the following procedure applies.
If AdvRte is obtained from an RREQ message, the link to the next hop
neighbor may not be confirmed as bidirectional (see Section 4.3). If
there is no existing matching route in the Local Route Set, AdvRte
MUST be installed to allow a corresponding RREP to be sent. If a
matching entry already exists, and the link to the neighbor can be
confirmed as bidirectional, AdvRte offers potential improvement.
The route update is applied as follows:
1. If no existing entry in the Local Route Set matches AdvRte's
address, prefix length, metric type and SeqNoRtr, continue to
Step 4 and create a new entry in the Local Route Set.
2. If two matching LocalRoutes exist in the Local Route Set, one is
a valid route, and one is an Unconfirmed route, AdvRte may offer
further improvement to the Unconfirmed route, or may offer an
update to the valid route.
* If AdvRte.NextHop's Neighbor.State is Heard, the advertised
route may offer improvement to the existing valid route, if
the link to the next hop can be confirmed as bidirectional.
Continue processing from Step 5 to update the existing
Unconfirmed LocalRoute.
* If AdvRte.NextHop's Neighbor.State is Confirmed, the
advertised route offers an update or improvement to the
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existing valid route. Continue processing from Step 5 to
update the existing valid LocalRoute.
3. If only one matching LocalRoute exists in the Local Route Set:
* If AdvRte.NextHop's Neighbor.State is Confirmed, continue
processing from Step 5 to update the existing LocalRoute.
* If AdvRte.NextHop's Neighbor.State is Heard, AdvRte may offer
improvement the existing LocalRoute, if the link to
AdvRte.NextHop can be confirmed as bidirectional.
* If LocalRoute.State is Unconfirmed, AdvRte is an improvement
to an existing Unconfirmed route. Continue processing from
Step 5 to update the existing LocalRoute.
* If LocalRoute.State is Invalid, AdvRte can replace the
existing LocalRoute. Continue processing from Step 5 to
update the existing LocalRoute.
* If LocalRoute.State is Active or Idle, AdvRte SHOULD be stored
as an additional entry in the Local Route Set, with
LocalRoute.State set to Unconfirmed. Continue processing from
Step 4 to create a new LocalRoute.
4. Create an entry in the Local Route Set and initialize as follows:
* LocalRoute.Address := AdvRte.Address
* LocalRoute.PrefixLength := AdvRte.PrefixLength
* LocalRoute.MetricType := AdvRte.MetricType
5. Update the LocalRoute as follows:
* LocalRoute.SeqNum := AdvRte.SeqNum
* LocalRoute.NextHop := AdvRte.NextHop
* LocalRoute.NextHopInterface := interface on which RteMsg was
received
* LocalRoute.Metric := AdvRte.Cost
* LocalRoute.LastUsed := CurrentTime
* LocalRoute.LastSeqNumUpdate := CurrentTime
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* LocalRoute.SeqNoRtr := AdvRte.SeqNoRtr
6. If a new LocalRoute was created, or if the existing
LocalRoute.State is Invalid or Unconfirmed, update LocalRoute as
follows:
* LocalRoute.State := Unconfirmed (if the next hop's
Neighbor.State is Heard)
* LocalRoute.State := Idle (if the next hop's Neighbor.State is
Confirmed)
7. If an existing LocalRoute.State changed from Invalid or
Unconfirmed to become Idle, any matching Unconfirmed LocalRoute
with worse metric value SHOULD be expunged.
8. If an existing LocalRoute was updated with a better metric value,
any matching Unconfirmed LocalRoute with worse metric value
SHOULD be expunged.
9. If this update results in LocalRoute.State of Active or Idle,
which matches a route request which is still in progress, the
associated route request retry timers MUST be cancelled.
If this update to the Local Route Set results in two LocalRoutes to
the same address, the best LocalRoute will be Unconfirmed. In order
to improve the route used for forwarding, the router SHOULD try to
determine if the link to the next hop of that LocalRoute is
bidirectional, by using that LocalRoute to forward future RREPs and
request acknowledgements (see Section 7.2.1 and Section 7.3.
6.8. Suppressing Redundant Messages (Multicast Route Message Set)
When route messages are flooded in a MANET, an AODVv2 router may
receive several instances of the same message. Forwarding every one
of these would provide little additional benefit, while generating
unnecessary signaling traffic and consequently additional
interference.
Each AODVv2 router stores information about recently received route
messages in the AODVv2 Multicast Route Message Set (Section 4.6).
In this section, an entry in the Multicast Route Message Set will be
called a "multicast entry" for short. Each multicast entry SHOULD be
maintained for at least RteMsg_ENTRY_TIME after the last Timestamp
update in order to account for long-lived RREQs traversing the
network. An entry MUST be deleted when the sequence number is no
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longer valid, i.e., after MAX_SEQNUM_LIFETIME. Memory-constrained
devices MAY remove the entry before this time.
Received RteMsgs are tested against multicast entries containing
information about previously received route messages. A multicast
entry is considered to be compatible with a received RteMsg, or
another multicast entry, if they both contain the same OrigPrefix,
OrigPrefixLen, TargPrefix, and MetricType. A multicast entry is
considered to be comparable with a received RteMsg, or another
multicast entry, if they are compatible and if, in addition, they
both have the same SeqNoRtr. These terms will be used in the
following algorithm determining how to process a received RteMsg, and
whether or not the RteMsg is redundant.
If the received message is determined to be redundant, no forwarding
or response to the message is needed. A message is considered to be
redundant if either (a) a comparable newer (as determined by the
OrigSeqNum) entry has already been received with information about
the source and destination addresses of the route discovery operation
or (b) it cannot be determined whether the message is newer compared
to existing entries, but the received message metric value is not any
better than metric values in compatible multicast entries.
To use the received RteMsg to update the Multicast Route Message Set,
and to determine whether or not the received RteMsg requires
additional processing as specified in Section 7, perform the
following steps:
1. First, search for a comparable multicast entry. If there is no
such entry, then create a new entry as follows:
* RteMsg.OrigPrefix := OrigPrefix from the RteMsg
* RteMsg.OrigPrefixLen := the prefix length associated with
OrigPrefix
* RteMsg.TargPrefix := TargPrefix from the message
* RteMsg.SeqNoRtr := the SeqNoRtr associated with RteMsg if
present, otherwise the sequence number associated with
OrigPrefix, if RteMsg is an RREQ
* RteMsg.OrigSeqNum := the sequence number associated with
OrigPrefix, if RteMsg is an RREQ
* RteMsg.TargSeqNum := the sequence number associated with
TargPrefix, if RteMsg is an RREP
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* RteMsg.Metric := the metric value associated with OrigPrefix
in a received RREQ
* RteMsg.MetricType := the metric type associated with
RteMsg.Metric
* RteMsg.Interface := the network interface on which the RteMsg
was received.
* RteMsg.Timestamp := CurrentTime
* RteMsg.RemovalTime := CurrentTime + MAX_SEQNUM_LIFETIME
2. Otherwise, if there is a comparable multicast entry, first update
the timing information:
* RteMsg.Timestamp := CurrentTime
* RteMsg.RemovalTime := CurrentTime + MAX_SEQNUM_LIFETIME
Then compare sequence numbers using the technique described in
Section 4.4:
* If the multicast entry is newer compared to the received
RteMsg, drop the RteMsg and discontinue processing.
* Otherwise, if the sequence numbers are the same, and the
metric value for the multicast entry is no worse than the
metric value in the received RteMsg, drop the RteMsg and
discontinue processing.
Otherwise the RteMsg is newer than the multicast entry or has a
better metric. Continue as follows:
* RteMsg.OrigSeqNum := the sequence number associated with
OrigPrefix, if RteMsg is an RREQ
* RteMsg.TargSeqNum := the sequence number associated with
TargPrefix, if RteMsg is an RREP
* RteMsg.Metric := the metric value associated with OrigPrefix
in a received RREQ
3. Compare the metric values for any other compatible entries with
the updated multicast entry containing the information from the
received RteMsg. If any other compatible entry has a metric as
good or better than that from the received RteMsg, then drop the
RteMsg and discontinue processing.
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If processing for the RteMsg has not been discontinued according to
the above instructions, then continue processing the message as
specified in Section 7.1.3.
6.9. Suppressing Redundant Route Error Messages (Route Error Set)
In order to avoid flooding the network with RERR messages when a
stream of IP packets to an unreachable address arrives, an AODVv2
router SHOULD avoid creating duplicate messages by determining
whether an equivalent RERR has recently been sent. This is achieved
with the help of the Route Error Set (see Section 4.7).
To determine if a RERR should be created:
1. Search for an entry in the Route Error Set where:
* RerrMsg.UnreachableAddress == UnreachableAddress to be
reported
* RerrMsg.PktSource == PktSource to be included in the RERR
If a matching entry is found, no further processing is required
and the RERR SHOULD NOT be sent.
2. If no matching entry is found, a new entry with the following
properties is created, and the RERR is created and sent as
described in Section 7.4.1:
* RerrMsg.Timeout := CurrentTime + RERR_TIMEOUT
* RerrMsg.UnreachableAddress == UnreachableAddress to be
reported
* RerrMsg.PktSource == PktSource to be included in the RERR.
6.10. Local Route Set Maintenance
Route maintenance involves the following operations:
o monitoring LocalRoutes in the Local Route Set,
o updating LocalRoute.State to handle route timeouts,
o (for possibly unidirectional links) confirming a route to
OrigAddr,
o reporting routes that become Invalid.
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6.10.1. LocalRoute State Changes
During normal operation, AODVv2 does not require explicit timeouts to
manage the lifetime of a valid route. At any time, any LocalRoute
MAY be examined and updated according to the rules below. In case a
Routing Information Base is used for forwarding, the corresponding
RIB entry MUST be updated as soon as the state of a LocalRoute.State
changes. Otherwise, if timers are not used to prompt updates of
LocalRoute.State, the LocalRoute.State MUST be checked before IP
packet forwarding and before any operation based on LocalRoute.State.
Route timeout behaviour is as follows:
o An Unconfirmed route MUST be expunged at MAX_SEQNUM_LIFETIME after
LocalRoute.LastSeqNumUpdate.
o An Idle route MUST be marked as Active when used to forward an IP
packet.
o If an Idle route is not used to forward an IP packet within
MAX_IDLETIME, LocalRoute.State MUST be set to Invalid.
o An Invalid route SHOULD remain in the Local Route Set, since
LocalRoute.SeqNum is used to classify future information about
LocalRoute.Address as stale or fresh.
o In all cases, if the time since LocalRoute.LastSeqNumUpdate
exceeds MAX_SEQNUM_LIFETIME, LocalRoute.SeqNum must be set to 0.
This is required so that any AODVv2 routers following the
initialization procedure can safely begin routing functions using
a new sequence number. A LocalRoute with LocalRoute.State set to
Active or Idle can remain in the Local Route Set after the
sequence number has been set to 0, for example if the route is
reliably carrying traffic. If LocalRoute.State is Invalid, or
later becomes Invalid, the LocalRoute MUST be expunged from the
Local Route Set.
LocalRoutes can become Invalid before a timeout occurs, as follows:
o If an external mechanism reports a link as broken, all LocalRoutes
using that link for LocalRoute.NextHop MUST immediately have
LocalRoute.State set to Invalid.
o LocalRoute.State MUST immediately be set to Invalid if a Route
Error (RERR) message is received where:
* The sender is LocalRoute.NextHop, or PktSource is a Router
Client address
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* There is an Address in AddressList which matches
LocalRoute.Address, and:
+ The prefix length associated with this Address, if any,
matches LocalRoute.PrefixLength
+ The sequence number associated with this Address, if any, is
newer or equal to LocalRoute.SeqNum (see Section 4.4)
+ The metric type associated with this Address matches
LocalRoute.MetricType
A LocalRoute can be Confirmed by inferring connectivity to OrigAddr.
o When an AODVv2 router sends an RREP to OrigAddr for destination
TargAddr, and subsequently the AODVv2 router receives a packet
from OrigAddr with destination TargAddr, the AODVv2 router infers
that the route to OrigAddr has been confirmed. The corresponding
state for LocalRoute.OrigAddr is changed to Active.
LocalRoutes are updated when Neighbor.State is updated:
o While the value of Neighbor.State is set to Heard, any routes in
the Local Route Set using that neighbor as a next hop MUST have
LocalRoute.State set to Unconfirmed.
o When the value of Neighbor.State is set to Blacklisted, any valid
routes in the Local Route Set using that neighbor for their next
hop MUST have LocalRoute.State set to Invalid.
o When a Neighbor Set entry is removed, all routes in the Local
Route Set using that neighbor as next hop MUST have
LocalRoute.State set to Invalid.
Memory constrained devices MAY choose to expunge routes from the
AODVv2 Local Route Set at other times, but MUST adhere to the
following rules:
o An Active route MUST NOT be expunged, as it is in use. If
deleted, IP traffic forwarded to this router would prompt
generation of a Route Error message, necessitating a Route Request
to be generated by the originator's router to re-establish the
route.
o An Idle route SHOULD NOT be expunged, as it is still valid for
forwarding IP traffic. If deleted, this could result in dropped
IP packets and a Route Request could be multicasted to re-
establish the route.
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o Any Invalid route MAY be expunged. Least recently used Invalid
routes SHOULD be expunged first, since the sequence number
information is less likely to be useful.
o An Unconfirmed route MUST NOT be expunged if it was installed
within the last RREQ_WAIT_TIME, because it may correspond to a
route discovery in progress. A Route Reply message might be
received which needs to use the LocalRoute.NextHop information.
Otherwise, it MAY be expunged.
6.10.2. Reporting Invalid Routes
When LocalRoute.State changes from Active to Invalid as a result of a
broken link or a received Route Error (RERR) message, other AODVv2
routers MUST be informed by sending an RERR message containing
details of the invalidated route.
An RERR message MUST also be sent when an AODVv2 router receives an
RREP message to forward, but the LocalRoute to the OrigAddr in the
RREP has been lost or is marked as Invalid.
A packet or message triggering the RERR MUST be discarded.
Generation of an RERR message is described in Section 7.4.1.
7. AODVv2 Protocol Messages
AODVv2 defines four message types: Route Request (RREQ), Route Reply
(RREP), Route Reply Acknowledgement (RREP_Ack), and Route Error
(RERR).
Each AODVv2 message is defined as a set of data. Rules for the
generation, reception and forwarding of each message type are
described in the following sections. Section 8 discusses how the
data is mapped to [RFC5444] Message TLVs, Address Blocks, and Address
TLVs.
7.1. Route Request (RREQ) Message
Route Request messages are used in route discovery operations to
request a route to a specified target address. RREQ messages have
the following contents:
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+-----------------------------------------------------------------+
| msg_hop_limit |
+-----------------------------------------------------------------+
| AddressList |
+-----------------------------------------------------------------+
| PrefixLengthList (optional) |
+-----------------------------------------------------------------+
| OrigSeqNum, (optional) TargSeqNum |
+-----------------------------------------------------------------+
| MetricType |
+-----------------------------------------------------------------+
| OrigMetric |
+-----------------------------------------------------------------+
Figure 1: RREQ message contents
msg_hop_limit
The remaining number of hops allowed for dissemination of the RREQ
message.
AddressList
Contains:
* OrigPrefix, from the Router Client Set entry which includes
OrigAddr, the source address of the IP packet for which a route
is requested,
* TargPrefix, set to TargAddr, the destination address of the IP
packet for which a route is requested, and
* Optionally, if RouterClient.SeqNoRtr is true, the IP address of
OrigRtr -- i.e., the router that originated the Sequence Number
for this RREQ.
PrefixLengthList
Contains OrigPrefixLen, i.e., the length, in bits, of the prefix
associated with the Router Client Set entry which includes
OrigAddr. If omitted, the prefix length is equal to OrigAddr's
address length in bits.
OrigSeqNum
The sequence number associated with OrigPrefix.
TargSeqNum
A sequence number associated with an existing Invalid route to
TargAddr. This MAY be included if available.
MetricType
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The metric type associated with OrigMetric.
OrigMetric
The metric value associated with the route to OrigPrefix, as
determined by the sender of the message.
7.1.1. RREQ Generation
An RREQ is generated to discover a route when an IP packet needs to
be forwarded for a Router Client, and no valid route currently exists
for the packet's destination in the Routing Information Base.
If the limit for the rate of AODVv2 control message generation has
been reached, no message SHOULD be generated Section 6.5. Before
creating an RREQ, the router SHOULD check the Multicast Route Message
Set to see if a compatible RREQ has recently been sent for the
requested destination. If so, and the wait time for a reply has not
yet been reached, the router SHOULD continue to await a response
without generating a new RREQ. If the timeout has been reached, a
new RREQ MAY be generated. If buffering is configured, incoming IP
packets awaiting this route SHOULD be buffered until the route
discovery is completed.
To generate the RREQ, the router (referred to as RREQ_Gen) follows
this procedure:
1. Set msg_hop_limit := MAX_HOPCOUNT
2. Set AddressList := {OrigPrefix, TargPrefix}
3. For the PrefixLengthList:
* If OrigAddr is part of an address range configured as a Router
Client, set PrefixLengthList := {RouterClient.PrefixLength,
null}.
* Otherwise, omit PrefixLengthList.
* If RouterClient.SeqNoRtr is nonzero, then add the router's own
IP address to AddressList, with AddressType SeqNoRtr.
4. For OrigSeqNum:
* Increment the router Sequence Number as specified in
Section 4.4.
* Set OrigSeqNum := router Sequence Number.
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5. For TargSeqNum:
* If an Invalid route exists in the Local Route Set matching
TargAddr using longest prefix matching and has a valid
sequence number, set TargSeqNum := LocalRoute.SeqNum.
* If no Invalid route exists in the Local Route Set matching
TargAddr, or the route doesn't have a sequence number, omit
TargSeqNum.
6. Include MetricType and set the type accordingly
7. Find the Router Client Set entry where RouterClient.IPAddress ==
OrigPrefix:
* Set OrigMetric := RouterClient.Cost
This AODVv2 message is used to create a corresponding [RFC5444]
message (see Section 8) which is handed to the RFC5444 multiplexer
for further processing. By default, the multiplexer is instructed to
multicast RREQ messages to LL-MANET-Routers on all interfaces
configured for AODVv2 operation.
7.1.2. RREQ Reception
Upon receiving a Route Request, an AODVv2 router performs the
following steps:
1. Check and update the Neighbor Set according to Section 6.3
* If the sender has Neighbor.State set to Blacklisted, ignore
this RREQ for further processing.
2. Verify that the message contains the required data:
msg_hop_limit, OrigPrefix, TargPrefix, OrigSeqNum, and
OrigMetric, and that OrigPrefix and TargPrefix are valid address
prefixes
* If not, ignore this RREQ for further processing.
3. Check that the MetricType is supported and configured for use
* If not, ignore this RREQ for further processing.
4. Determine whether the cost of the advertised route will exceed
the maximum allowed metric value for the metric type (Metric <=
MAX_METRIC[MetricType] - Cost(L))
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* If it will, ignore this RREQ for further processing.
5. Process the route to OrigPrefix as specified in Section 6.7
6. Determine whether or not the information in the message is
redundant, by following the procedure in Section 6.8; if
redundant, ignore this RREQ for further processing.
7. Check if the TargPrefix matches an entry in the Router Client Set
* If so, generate an RREP as specified in Section 7.2.1.
* If not, continue to RREQ forwarding Section 7.2.3.
7.1.3. RREQ Forwarding
Forwarding or responding to a RteMsg provides up-to-date information
and improved metrics to other routers. If a RteMsg is not forwarded,
routes needed by applications may not be discovered.
By forwarding an RREQ, a router advertises that it will forward IP
packets to the OrigPrefix contained in the RREQ according to the
information enclosed. The router MAY choose not to forward the RREQ,
for example if the router is heavily loaded or low on energy and
therefore unwilling to advertise routing capability for more traffic.
This could, however, decrease connectivity in the network or result
in non-optimal paths.
The RREQ MUST NOT be forwarded if the received msg_hop_limit = 1, or
if the limit for the rate of AODVv2 control message generation has
been reached. Otherwise, the RREQ is updated and forwarded as
follows:
1. Set msg_hop_limit := received msg_hop_limit - 1
2. Set OrigMetric := LocalRoute[OrigPrefix].Metric
This modified RREQ is handed to the [RFC5444] multiplexer for further
processing. By default, the multiplexer is instructed to multicast
the message to LL-MANET-Routers on all interfaces configured for
AODVv2 operation.
7.2. Route Reply (RREP) Message
When a Route Request message is received, requesting a route to a
target address (TargAddr) which is configured as part of a Router
Client Set entry, a Route Reply message is sent in response. The
RREP offers a route to TargPrefix.
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RREP messages have the following contents:
+-----------------------------------------------------------------+
| msg_hop_limit |
+-----------------------------------------------------------------+
| AddressList |
+-----------------------------------------------------------------+
| PrefixLengthList (optional) |
+-----------------------------------------------------------------+
| TargSeqNum |
+-----------------------------------------------------------------+
| MetricType |
+-----------------------------------------------------------------+
| TargMetric |
+-----------------------------------------------------------------+
Figure 2: RREP message contents
msg_hop_limit
The remaining number of hops allowed for dissemination of the RREP
message.
AddressList
Contains:
* OrigPrefix, from the Router Client entry which includes
OrigAddr, the source address of the IP packet for which a route
is requested
* TargPrefix, set to TargAddr, the destination address of the IP
packet for which a route is requested.
* Optionally, if RouterClient.SeqNoRtr is true, the IP address of
TargRtr -- i.e., the router that originated the Sequence Number
for this RREP.
PrefixLengthList
Contains TargPrefixLen, i.e., the length, in bits, of the prefix
associated with the Router Client Set entry which includes
TargAddr. If omitted, the prefix length is equal to TargAddr's
address length, in bits.
TargSeqNum
The sequence number associated with TargPrefix.
MetricType
The metric type associated with TargMetric.
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TargMetric
The metric value associated with the route to TargPrefix, as seen
from the sender of the message.
7.2.1. RREP Generation
A Route Reply message is generated when a Route Request for a Router
Client of the AODVv2 router arrives. This is the case when
RteMsg.TargPrefix matches an entry in the Router Client Set of the
AODVv2 router.
Before creating an RREP, the router SHOULD check whether
CONTROL_TRAFFIC_LIMIT has been reached. If so, the RREP SHOULD NOT
be created.
The RREP will traverse the path of the route to OrigPrefix. If the
best route to OrigPrefix in the Local Route Set is Unconfirmed, the
link to the next hop neighbor is not yet confirmed as bidirectional
(see Section 6.2). In this case an RREP_Ack MUST also be sent as
described in Section 7.3, in order to request an acknowledgement
message from the next hop router to prove that the link is
bidirectional. If the best route to OrigPrefix in the Local Route
Set is valid, the link to the next hop neighbor is already confirmed
as bidirectional, and no acknowledgement is required.
Implementations MAY allow a number of retries of the RREP if a
requested acknowledgement is not received within
RREP_Ack_SENT_TIMEOUT, doubling the timeout with each retry, up to a
maximum of RREP_RETRIES, using the same exponential backoff described
in Section 6.6 for RREQ retries. The acknowledgement MUST be
considered to have failed after the wait time for an RREP_Ack
response to the final RREP.
To generate the RREP, the router (also referred to as RREP_Gen)
follows this procedure:
1. Set msg_hop_limit := MAX_HOPCOUNT - msg_hop_limit from the
received RREQ message
2. Set Address List := {OrigPrefix, TargPrefix}
* If RouterClient.SeqNoRtr is nonzero, then add the router's own
IP address to AddressList, with AddressType SeqNoRtr.
3. For the PrefixLengthList:
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* If TargAddr is part of an address range configured as a Router
Client, set PrefixLengthList := {null,
RouterClient.PrefixLength}.
* Otherwise, omit PrefixLengthList.
4. For the TargSeqNum:
* Increment the router Sequence Number as specified in
Section 4.4.
* Set TargSeqNum := router Sequence Number.
5. Include MetricType and set the type to match the MetricType in
the received RREQ message.
6. Set TargMetric := RouterClient.Cost for the Router Client Set
entry which includes TargAddr.
This AODVv2 message is used to create a corresponding [RFC5444]
message (see Section 8) which is handed to the RFC5444 multiplexer
for further processing. The multiplexer is instructed to unicast the
RREP to LocalRoute[OrigPrefix].NextHop. The RREP MUST be sent over
LocalRoute[OrigPrefix].NextHopInterface.
7.2.2. RREP Reception
Upon receiving a Route Reply, an AODVv2 router performs the following
steps:
1. Verify that the message contains the required data:
msg_hop_limit, OrigPrefix, TargPrefix, TargSeqNum, and
TargMetric, and that OrigPrefix and TargPrefix are valid
addresses
* If not, ignore this RREP for further processing.
2. Check that the MetricType is supported and configured for use
* If not, ignore this RREP for further processing.
3. If this RREP does not correspond to an RREQ generated or
forwarded in the last RREQ_WAIT_TIME, ignore for further
processing.
4. If the Multicast Route Message Set does not contain an entry
where:
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o RteMsg.OrigPrefix == RREP.OrigPrefix
o RteMsg.OrigPrefixLen == RREP.OrigPrefixLen
o RteMsg.TargAddr exists within RREP.TargPrefix
o RteMsg.OrigSeqNum <= RREP.OrigSeqNum
o RteMsg.SeqNoRtr = RREP.SeqNoRtr
o RteMsg.MetricType == RREP.MetricType
o RteMsg.Timestamp > CurrentTime - RREQ_WAIT_TIME
o RteMsg.Interface == The interface on which the RREP was received
then, ignore this RREP for further processing, since it does not
correspond to a previously sent RREQ. Otherwise continue as follows:
1. Update the Neighbor Set according to Section 6.3
2. Determine whether the cost of the advertised route exceeds the
maximum allowed metric value for the metric type (Metric <=
MAX_METRIC[MetricType] - Cost(L))
* If it does, ignore this RREP for further processing.
3. Process the route to TargPrefix as specified in Section 6.7
4. Determine whether the message is redundant by comparing to
entries in the Multicast Route Message Set (Section 6.8)
* If redundant, ignore this RREP for further processing.
* If not redundant, save the information in the Multicast Route
Message Set to identify future redundant RREP messages and
continue processing.
5. Determine whether the OrigPrefix matches an entry in the Router
Client Set
* If so, no further processing is necessary.
* If not, continue to the next step.
6. Determine whether a valid (Active or Idle) or Unconfirmed
LocalRoute exists to OrigPrefix
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* If so, continue to RREP forwarding Section 7.2.3.
* If not, a Route Error message SHOULD be transmitted toward
TargPrefix according to Section 7.4.1; the RREP MUST be
discarded and not forwarded.
7.2.3. RREP Forwarding
A received Route Reply message is forwarded toward OrigPrefix. By
forwarding the RREP, a router advertises that it has a route to
TargPrefix.
The RREP MUST NOT be forwarded if the received msg_hop_limit = 1, or
if CONTROL_TRAFFIC_LIMIT has been reached. Otherwise, the router
MUST forward the RREP.
The procedure for RREP forwarding is as follows:
1. Set msg_hop_limit := received msg_hop_limit - 1
2. If the link to the next hop router toward OrigAddr is not known
to be bidirectional, also verify bidirectionality (see
Section 6.2).
3. Set TargMetric := LocalRoute[TargPrefix].Metric
This modified message is handed to the [RFC5444] multiplexer for
further processing. The multiplexer is instructed to unicast the
RREP to LocalRoute[OrigPrefix].NextHop. The RREP MUST be sent over
LocalRoute[OrigPrefix].NextHopInterface.
7.3. Route Reply Acknowledgement (RREP_Ack) Message
The Route Reply Acknowledgement is used as both a request and a
response message to test bidirectionality of a link over which a
Route Reply has also been sent. The router which forwards the RREP
MUST send a Route Reply Acknowledgement message to the intended next
hop, if the link to the next hop neighbor is not yet confirmed as
bidirectional.
The receiving router MUST then reply with a Route Reply
Acknowledgement response message.
When the Route Reply Acknowledgement response message is received by
the sender of the RREP, it confirms that the link between the two
routers is bidirectional (see Section 6.2).
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If the Route Reply Acknowledgement is not received within
RREP_Ack_SENT_TIMEOUT, the link is determined to be unidirectional.
+-----------------------------------------------------------------+
| AckReq (optional) |
+-----------------------------------------------------------------+
Figure 3: RREP_Ack message contents
7.3.1. RREP_Ack Request Generation
An RREP_Ack MUST be generated if a Route Reply is sent over a link
which is not known to be bidirectional. It includes an AckReq
element to indicate that it is a request for acknowledgement.
The RREP_Ack SHOULD NOT be generated if the limit for the rate of
AODVv2 control message generation has been reached.
The [RFC5444] representation of the RREP_Ack is discussed in
Section 8.
RREP_Ack requests MUST be unicast to LocalRoute[OrigPrefix].NextHop
via LocalRoute[OrigPrefix].NextHopInterface. The multiplexer SHOULD
be instructed to send the RREP_Ack in the same [RFC5444] packet as
the RREP.
The Neighbor Set entry for LocalRoute[OrigPrefix].NextHop MUST also
be updated to indicate that an RREP_Ack is required (see
Section 6.3).
7.3.2. RREP_Ack Reception
Upon receiving an RREP_Ack, an AODVv2 router performs the following
steps:
1. Determine whether an AckReq element is included:
* If so, create an RREP_Ack Response as described in
Section 7.3.3. No further processing is required.
* If not, continue to the next step.
2. Determine whether the Neighbor Set contains an entry where:
* Neighbor.IPAddress == IP.SourceAddress of the RREP_Ack message
* Neighbor.State == Heard
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* Neighbor.Timeout < CurrentTime
* Neighbor.Interface matches the interface on which the RREP_Ack
was received
If no such entry is found, the RREP_Ack was not expected; no
actions are required and processing ends. Otherwise, the router
sets Neighbor.Timeout to INFINITY_TIME, and processing continues
to the next step.
3. Update the Neighbor Set according to Section 6.3, including
updating routes using this Neighbor as LocalRoute.NextHop.
7.3.3. RREP_Ack Response Generation
An RREP_Ack response MUST be generated if a received RREP_Ack
includes an AckReq, unless the limit for the rate of AODVv2 control
message generation has been reached in which case the RREP_Ack
response SHOULD NOT be generated.
There is no further data in an RREP_Ack response. The [RFC5444]
representation is discussed in Section 8. In this case, the
multiplexer is instructed to unicast the RREP_Ack to the source IP
address of the RREP_Ack message that requested it, over the same
interface on which the RREP_Ack was received.
7.4. Route Error (RERR) Message
A Route Error message is generated by an AODVv2 router to notify
other AODVv2 routers about routes that are no longer available. An
RERR message has the following contents:
+-----------------------------------------------------------------+
| PktSource (optional) |
+-----------------------------------------------------------------+
| AddressList |
+-----------------------------------------------------------------+
| PrefixLengthList (optional) |
+-----------------------------------------------------------------+
| SeqNumList (optional) |
+-----------------------------------------------------------------+
| MetricTypeList |
+-----------------------------------------------------------------+
Figure 4: RERR message contents
PktSource
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The source address of the IP packet triggering the RERR. If the
RERR is triggered by a broken link, PktSource is not required.
AddressList
The addresses of the routes not available through RERR_Gen.
PrefixLengthList
The prefix lengths, in bits, associated with the routes not
available through RERR_Gen. These values indicate whether routes
represent a single device or an address range.
SeqNumList
The sequence numbers (where known) of the routes not available
through RERR_Gen.
MetricTypeList
The metric types associated with the routes not available through
RERR_Gen.
7.4.1. RERR Generation
A Route Error message is generated when an AODVv2 router (also
referred to as RERR_Gen) needs to report that a destination is not
reachable. There are three events that cause this response:
o When an IP packet that has been forwarded from another router, but
there is no valid route in the Routing Information Base for its
destination, the source of the packet needs to be informed that
the route to the destination of the packet does not exist. The
RERR generated MUST include PktSource set to the source address of
the IP packet, and MUST contain only one unreachable address in
the AddressList, i.e., the destination address of the IP packet.
RERR_Gen MUST discard the IP packet that triggered generation of
the RERR. The prefix length, sequence number and metric type
SHOULD be included if known from an existing Invalid LocalRoute to
the unreachable address.
o When an RREP message cannot be forwarded because the LocalRoute to
OrigPrefix has been lost or is Invalid, RREP_Gen needs to be
informed that the route to OrigPrefix does not exist. The RERR
generated MUST include PktSource set to the TargPrefix of the
RREP, and MUST contain only one unreachable address in the
AddressList, the OrigPrefix from the RREP. RERR_Gen MUST discard
the RREP message that triggered generation of the RERR. The
prefix length, sequence number and metric type SHOULD be included
if known from an Invalid LocalRoute to the unreachable address.
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o When a link breaks, multiple LocalRoutes may become Invalid, and
the RERR generated MAY contain multiple unreachable addresses.
The RERR MUST include MetricTypeList. PktSource is omitted. All
previously Active LocalRoutes that used the broken link MUST be
reported. The AddressList, SeqNumList, and MetricTypeList will
contain entries for each LocalRoute which has become Invalid.
PrefixLengthList will be included if needed to report invalid
routes to a non-default prefix. An RERR message is only sent if
an Active LocalRoute becomes Invalid, though an AODVv2 router can
also include Idle LocalRoutes that become Invalid if the
configuration parameter ENABLE_IDLE_IN_RERR is set (see
Section 12.3).
The RERR SHOULD NOT be generated if CONTROL_TRAFFIC_LIMIT has been
reached. The RERR also SHOULD NOT be generated if it is a duplicate,
as determined by Section 6.9.
Incidentally, if an AODVv2 router receives an ICMP error packet to or
from the address of one of its Router Clients, it forwards the ICMP
packet in the same way as any other IP packet, and will not generate
any RERR message based on the contents of the ICMP packet.
To generate the RERR, the router follows this procedure:
1. If necessary, include PktSource and set the value as given above
2. For each LocalRoute that needs to be reported:
* Insert LocalRoute.Address into the AddressList.
* Insert LocalRoute.PrefixLength into PrefixLengthList, if known
and not equal to the address length.
* Insert LocalRoute.SeqNum into SeqNumList, if known.
* Insert LocalRoute.MetricType into MetricTypeList.
The AODVv2 message is used to create a corresponding [RFC5444]
message (see Section 8).
If the RERR is sent in response to an undeliverable IP packet or RREP
message (i.e., if PktSource is included), the RERR SHOULD be sent
unicast to the next hop on the route to PktSource. It MUST be sent
over the same interface on which the undeliverable IP packet was
received. If there is no route to PktSource, the RERR SHOULD be
multicast to LL-MANET-Routers. If the RERR is sent in response to a
broken link, i.e., PktSource is not included, the RERR is, by
default, multicast to LL-MANET-Routers.
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Section 10 describes processing steps when the optional precursor
lists feature is implemented.
7.4.2. RERR Reception
Upon receiving a Route Error, an AODVv2 router performs the following
steps:
1. Determine whether the message contains at least one unreachable
address; if not, ignore this RERR for further processing.
Otherwise continue as follows:
2. For each address in the AddressList, check that:
* The address is valid (routable and unicast).
* The MetricType is supported and configured for use.
* There is a LocalRoute with the same MetricType matching the
address using longest prefix matching.
* Either the LocalRoute's next hop is the sender of the RERR and
the next hop interface is the interface on which the RERR was
received, or PktSource is present in the RERR and is a Router
Client address.
* The unreachable address' sequence number is either unknown, or
is no less than the LocalRoute's sequence number.
If any of the above are false the address does not match a
LocalRoute and MUST NOT be processed or regenerated in a RERR.
If all of the above are true, the LocalRoute which matches the
unreachable address MUST be marked as Invalid. Otherwise,
regeneration of the RERR proceeds as follows. If the LocalRoute
was previously Active, it MUST be reported in a regenerated RERR.
If the LocalRoute was previously Idle, it MAY be reported in a
regenerated RERR, if ENABLE_IDLE_IN_RERR is configured. The
Local Route Set MUST be updated according to these rules:
* If the LocalRoute's prefix length is the same as the
unreachable address' prefix length, set LocalRoute.State to
Invalid.
* If the LocalRoute's prefix length is longer than the
unreachable address' prefix length, the LocalRoute MUST be
expunged from the Local Route Set, since it is a sub-route of
the route which is reported to be Invalid.
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* If the prefix length is different, create a new LocalRoute
with the unreachable address, and its prefix length and
sequence number, and set LocalRoute.State to Invalid. These
Invalid routes are retained to avoid processing stale
messages.
* Update the sequence number on the existing LocalRoute, if the
reported sequence number is determined to be newer using the
comparison method described in Section 4.4.
3. If there are previously Active LocalRoutes that MUST be reported,
regenerate the RERR as detailed in Section 7.4.3.
7.4.3. RERR Regeneration
The Route Error message SHOULD NOT be regenerated if
CONTROL_TRAFFIC_LIMIT has been reached.
The procedure for RERR regeneration is as follows:
1. If PktSource was included in the received RERR, and PktSource is
not a Router Client, copy it into the regenerated RERR
2. For each LocalRoute that needs to be reported as identified in
Section 7.4.1:
* Insert LocalRoute.Address into the AddressList.
* Insert LocalRoute.PrefixLength into PrefixLengthList, if known
and not equal to the address length.
* Insert LocalRoute.SeqNum into SeqNumList, if known.
* Insert LocalRoute.MetricType into MetricTypeList.
The AODVv2 message is used to create a corresponding [RFC5444]
message (see Section 8). If the RERR contains PktSource, the
regenerated RERR SHOULD be sent unicast to the next hop on the
LocalRoute to PktSource. It MUST be sent over the same interface on
which the undeliverable IP packet was received. If there is no route
to PktSource, or PktSource is a Router Client, it SHOULD be multicast
to LL-MANET-Routers. If the RERR is sent in response to a broken
link, the RERR is, by default, multicast to LL-MANET-Routers.
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8. RFC 5444 Representation
AODVv2 specifies that all control messages between routers MUST use
the Generalized Mobile Ad Hoc Network Packet/Message Format
[RFC5444], and therefore AODVv2's route messages comprise data which
is mapped to message elements in [RFC5444].
[RFC5444] provides a multiplexed transport for multiple protocols.
An [RFC5444] implementation MAY choose to optimize the content of
certain elements during message creation to reduce control message
overhead.
A brief summary of the [RFC5444] format:
1. A packet contains zero or more messages
2. A message contains a Message Header, one Message TLV Block, zero
or more Address Blocks, and one Address Block TLV Block per
Address Block
3. The Message TLV Block contains zero or more Message TLVs
4. An Address Block TLV Block includes zero or more Address Block
TLVs
5. Each TLV value in an Address Block TLV Block can be associated
with all of the addresses, or with a contiguous set of addresses,
or with a single address in the Address Block
AODVv2 does not require access to the [RFC5444] packet header.
In the message header, AODVv2 uses <msg-type>, <msg-hop-limit> and
<msg-addr-length>. The <msg-addr-length> field indicates the length
of any addresses in the message, using <msg-addr-length> := (address
length in octets - 1), i.e. 3 for IPv4 and 15 for IPv6.
The addresses in an Address Block MAY appear in any order, and values
in a TLV in the Address Block TLV Block must be associated with the
correct address in the Address Block by the [RFC5444] implementation.
To indicate which value is associated with each address, the AODVv2
message representation uses lists where the order of the addresses in
the AODVv2 AddressList matches the order of values in other data
lists, e.g., the order of SeqNums in the SeqNumList in an RERR.
[RFC5444] maps this information to Address Block TLVs associated with
the relevant addresses in the Address Block.
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Each address included in the Address Block is identified as
OrigPrefix, TargPrefix, PktSource, SeqNoRtr, or Unreachable Address
by including an ADDRESS_TYPE TLV in the Address Block TLV Block.
The following sections show how AODVv2 data is represented in
[RFC5444] messages. In Section 13.3, AODVv2 defines several new
TLVs.
Where the extension type of a TLV is set to zero, this is the default
[RFC5444] value and the extension type will not be included in the
message.
8.1. Route Request Message Representation
8.1.1. Message Header
+---------------+-----------------+---------------------------------+
| Data | Header Field | Value |
+---------------+-----------------+---------------------------------+
| None | <msg-type> | RREQ |
| msg_hop_limit | <msg-hop-limit> | MAX_HOPCOUNT, reduced by number |
| | | of hops traversed so far by the |
| | | message. |
+---------------+-----------------+---------------------------------+
8.1.2. Message TLV Block
AODVv2 does not define any Message TLVs for an RREQ message.
8.1.3. Address Block
An RREQ contains OrigPrefix and TargPrefix, and each of these
addresses has an associated prefix length. If the prefix length has
not been included in the AODVv2 message, it is equal to the address
length in bits.
+---------------------------+------------------------------+
| Data | Address Block |
+---------------------------+------------------------------+
| OrigPrefix/OrigPrefixLen | <address> + <prefix-length> |
| TargPrefix/TargPrefixLen | <address> + <prefix-length> |
| SeqNoRtr/PrefixLen | <address> + <prefix-length> |
+---------------------------+------------------------------+
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8.1.4. Address Block TLV Block
Address Block TLVs are always associated with one or more addresses
in the Address Block. The following sections show the TLVs that
apply to each address.
8.1.4.1. Address Block TLVs for OrigPrefix
+-------------+--------------+------------+-------------------------+
| Data | TLV Type | Extension | Value |
| | | Type | |
+-------------+--------------+------------+-------------------------+
| None | ADDRESS_TYPE | 0 | ORIGPREFIX |
| OrigSeqNum | SEQ_NUM | 0 | Sequence number of |
| | | | RREQ_Gen, the router |
| | | | which initiated route |
| | | | discovery. |
| OrigMetric | PATH_METRIC | MetricType | Metric value for the |
| /MetricType | | | route to OrigPrefix, |
| | | | using MetricType. |
+-------------+--------------+------------+-------------------------+
8.1.4.2. Address Block TLVs for TargPrefix
+------------+--------------+-------------+-------------------------+
| Data | TLV Type | Extension | Value |
| | | Type | |
+------------+--------------+-------------+-------------------------+
| None | ADDRESS_TYPE | 0 | TARGPREFIX |
| TargSeqNum | SEQ_NUM | 0 | The last known |
| | | | TargSeqNum for |
| | | | TargPrefix. |
+------------+--------------+-------------+-------------------------+
8.2. Route Reply Message Representation
8.2.1. Message Header
+---------------+-----------------+---------------------------------+
| Data | Header Field | Value |
+---------------+-----------------+---------------------------------+
| None | <msg-type> | RREP |
| msg_hop_limit | <msg-hop-limit> | MAX_HOPCOUNT - msg_hop_limit |
| | | from the corresponding RREQ, |
| | | reduced by number of hops |
| | | traversed so far by the |
| | | message. |
+---------------+-----------------+---------------------------------+
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8.2.2. Message TLV Block
AODVv2 does not define any Message TLVs for an RREP message.
8.2.3. Address Block
An RREP contains OrigPrefix and TargPrefix, and each of these
addresses has an associated prefix length. If the prefix length has
not been included in the AODVv2 message, it is equal to the address
length in bits.
+---------------------------+------------------------------+
| Data | Address Block |
+---------------------------+------------------------------+
| OrigPrefix/OrigPrefixLen | <address> + <prefix-length> |
| TargPrefix/TargPrefixLen | <address> + <prefix-length> |
| SeqNoRtr/PrefixLen | <address> + <prefix-length> |
+---------------------------+------------------------------+
8.2.4. Address Block TLV Block
Address Block TLVs are always associated with one or more addresses
in the Address Block. The following sections show the TLVs that
apply to each address.
8.2.4.1. Address Block TLVs for OrigPrefix
+-------+---------------+-----------------+-------------+
| Data | TLV Type | Extension Type | Value |
+-------+---------------+-----------------+-------------+
| None | ADDRESS_TYPE | 0 | ORIGPREFIX |
+-------+---------------+-----------------+-------------+
8.2.4.2. Address Block TLVs for TargPrefix
+--------------+--------------+------------+------------------------+
| Data | TLV Type | Extension | Value |
| | | Type | |
+--------------+--------------+------------+------------------------+
| None | ADDRESS_TYPE | 0 | TARGPREFIX |
| TargSeqNum | SEQ_NUM | 0 | Sequence number of |
| | | | RREP_Gen, the router |
| | | | which created the |
| | | | RREP. |
| TargMetric | PATH_METRIC | MetricType | Metric value for the |
| /MetricType | | | route to TargPrefix, |
| | | | using MetricType. |
+--------------+--------------+------------+------------------------+
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8.3. Route Reply Acknowledgement Message Representation
8.3.1. Message Header
+-------+---------------+-----------+
| Data | Header Field | Value |
+-------+---------------+-----------+
| None | <msg-type> | RREP_Ack |
+-------+---------------+-----------+
8.3.2. Message TLV Block
AODVv2 defines an AckReq Message TLV, included when an
acknowledgement of this message is required, in order to monitor
adjacency, as described in Section 6.2.
+---------+-----------+-----------------+--------+
| Data | TLV Type | Extension Type | Value |
+---------+-----------+-----------------+--------+
| AckReq | ACK_REQ | 0 | None |
+---------+-----------+-----------------+--------+
8.3.3. Address Block
AODVv2 does not define an Address Block for an RREP_Ack message.
8.3.4. Address Block TLV Block
AODVv2 does not define any Address Block TLVs for an RREP_Ack
message.
8.4. Route Error Message Representation
Route Error Messages MAY be split into multiple [RFC5444] messages
when the desired contents would exceed the MTU. However, all of the
resulting messages MUST have the same message header as described
below. If PktSource is included in the AODVv2 message, it MUST be
included in all of the resulting [RFC5444] messages.
8.4.1. Message Header
+-------+---------------+--------+
| Data | Header Field | Value |
+-------+---------------+--------+
| None | <msg-type> | RERR |
+-------+---------------+--------+
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8.4.2. Message TLV Block
AODVv2 does not define any Message TLVs for an RERR message.
8.4.3. Address Block
The Address Block in an RERR MAY contain PktSource, the source
address of the IP packet triggering RERR generation, as detailed in
Section 7.4. The prefix length associated with PktSource is equal to
the address length in bits.
Address Block always contains one address per route that is no longer
valid, and each address has an associated prefix length. If a prefix
length has not been included for this address, it is equal to the
address length in bits.
+------------------------------+------------------------------------+
| Data | Address Block |
+------------------------------+------------------------------------+
| PktSource | <address> + <prefix-length> for |
| | PktSource |
| AddressList/PrefixLengthList | <address> + <prefix-length> for |
| | each unreachable address in |
| | AddressList |
+------------------------------+------------------------------------+
8.4.4. Address Block TLV Block
Address Block TLVs are always associated with one or more addresses
in the Address Block. The following sections show the TLVs that
apply to each type of address in the RERR.
8.4.4.1. Address Block TLVs for PktSource
+------------+---------------+-----------------+------------+
| Data | TLV Type | Extension Type | Value |
+------------+---------------+-----------------+------------+
| PktSource | ADDRESS_TYPE | 0 | PKTSOURCE |
+------------+---------------+-----------------+------------+
8.4.4.2. Address Block TLVs for Unreachable Addresses
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+----------------+--------------+------------+----------------------+
| Data | TLV Type | Extension | Value |
| | | Type | |
+----------------+--------------+------------+----------------------+
| None | ADDRESS_TYPE | 0 | UNREACHABLE |
| SeqNumList | SEQ_NUM | 0 | Sequence number |
| | | | associated with |
| | | | invalid route to the |
| | | | unreachable address. |
| MetricTypeList | PATH_METRIC | MetricType | None. Extension Type |
| | | | set to MetricType of |
| | | | the route to the |
| | | | unreachable address. |
+----------------+--------------+------------+----------------------+
9. Simple External Network Attachment
Figure 5 shows a stub (i.e., non-transit) network of AODVv2 routers
which is attached to an external network (i.e., a network not using
AODVv2) via a single External Network Access Router (ENAR).
As in any externally-attached network, AODVv2 routers and Router
Clients that wish to be reachable from the external network MUST have
IP addresses within the ENAR's routable and topologically correct
prefix (e.g., 191.0.2.0/24 in Figure 5). This AODVv2 network and
networks attached to routers within it will be advertised to the
external network using other routing protocols or procedures which
are out of scope for this specification.
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/-------------------------\
/ +----------------+ \
/ | AODVv2 Router | \
| | 191.0.2.2/32 | |
| +----------------+ | Routable
| +-----+--------+ Prefix
| | ENAR | /191.0.2.0/24
| | AODVv2 Router| /
| | 191.0.2.1 |/ /---------------\
| | serving net +------+ External \
| | 191.0.2.0/24 | \ Network /
| +-----+--------+ \---------------/
| +----------------+ |
| | AODVv2 Router | |
| | 191.0.2.3/32 | |
\ +----------------+ /
\ /
\-------------------------/
Figure 5: Simple External Network Attachment Example
When an AODVv2 router within the AODVv2 MANET wants to discover a
route toward an address on the external network, it uses the normal
AODVv2 route discovery for that IP Destination Address.
The ENAR MUST respond to RREQ on behalf of all external network
destinations, that is, destinations which are not on the configured
191.0.2.0 /24 network. The ENAR MUST NOT respond with a TargPrefix
and TargPrefixLen which includes any of the networks configured as
part of the AODVv2 network. Sending a Route Request for a gateway is
not currently supported.
If more than one gateway is configured to serve the same external
network, each such gateway MUST configure that external network as a
Router Client with its IP address as the value of SeqNoRtr for the
RouterClient. AODVv2 messages SHOULD NOT be transmitted to routers
in the External Network.
RREQs for addresses inside the AODVv2 network, e.g. destinations on
the configured 191.0.2.0/24 network, are handled using the standard
processes described in Section 7. Note that AODVv2 does not
currently support route discovery for prefixes that do not equal
address length, but RREPs do advertise the prefix on which TargAddr
resides.
When an IP packet from an address on the external network destined
for an address in the AODVv2 MANET reaches the ENAR, if the ENAR does
not have a route toward that destination in its Routing Information
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Base, it will perform normal AODVv2 route discovery for that
destination.
Configuring the ENAR as a default router is outside the scope of this
specification.
10. Precursor Lists
This section specifies an interoperable, optional enhancement to
AODVv2 enabling more economical Route Error notifications.
There can be several sources of traffic for a certain destination.
Each source of traffic and each upstream router between the
forwarding AODVv2 router and the traffic source is known as a
"precursor" for the destination. For each destination, an AODVv2
router MAY choose to keep track of precursors that have provided
traffic for that destination. Route Error messages about that
destination can then be sent unicast to these precursors instead of
multicast to all AODVv2 routers.
Since an RERR will be regenerated if it comes from a next hop on a
valid LocalRoute, the RERR SHOULD ideally be sent backwards along the
route that the source of the traffic uses, to ensure it is
regenerated at each hop and reaches the traffic source. If the
reverse path is unknown, the RERR SHOULD be sent toward the source
along any available route. Therefore, the options for saving
precursor information are as follows:
o Save the next hop on an existing route to the IP packet's source
address as the precursor. In this case, it is not guaranteed that
an RERR that is sent will follow the reverse of the source's
route. In rare situations, this may prevent the route from being
invalidated at the source of the data traffic.
o Save the IP packet's source address as the precursor. In this
case, the RERR can be sent along any existing route to the source
of the data traffic, and SHOULD include PktSource to ensure that
the route will be invalidated at the source of the traffic, in
case the RERR does not follow the reverse of the source's route.
o By inspecting the MAC address of each forwarded IP packet,
determine which router forwarded the packet, and save the router
address as a precursor. This ensures that when an RERR is sent to
the precursor router, the route will be invalidated at that
router, and the RERR will be regenerated toward the source of the
IP packet.
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During normal operation, each AODVv2 router maintaining precursor
lists for a LocalRoute must update the precursor list whenever it
uses this route to forward traffic to the destination. Precursors
are classified as Active if traffic has recently been forwarded by
the precursor. The precursor is marked with a timestamp to indicate
the time it last forwarded traffic on this route.
When an AODVv2 router detects that one or more LocalRoutes are
broken, it MAY notify each Active precursor using a unicast Route
Error message instead of creating multicast traffic. Unicast is
applicable when there are few Active precursors compared to the
number of neighboring AODVv2 routers. However, the default multicast
behavior is still preferable when there are many precursors, since
fewer message transmissions are required.
When an AODVv2 router supporting precursor lists receives an RERR
message, it SHOULD identify the list of its own affected Active
precursors for the routes in the RERR, and choose to send a unicast
RERR to those, rather than send a multicast RERR.
When a LocalRoute is expunged, any precursor list associated with it
MUST also be expunged.
11. Application of RFC 7182 to AODVv2
Implementations of AODVv2 MUST support ICV TLVs using type-extensions
1 and 2, hash-function HASH_FUNCTION, and cryptographic function
CRYPTOGRAPHIC_FUNCTION. An ICV MUST be included with every message.
The ICV value MAY be truncated as specified in [RFC7182].
Since the msg-hop-limit and PATH_METRIC values are mutable when
included in AODVv2 messages, these values are set to zero before
calculating an ICV. This means that these values are not protected
end-to-end and are therefore susceptible to manipulation. This form
of attack is described in Section 14.3.2.
Implementations of AODVv2 MUST support a TIMESTAMP TLV using type-
extension 0. The timestamp used is a sequence number, and therefore
the length of the <TIMESTAMP-value> field matches the AODVv2 sequence
number defined in Section 4.4. The TIMESTAMP TLV MUST be included in
RREP_Ack and RERR messages.
When more than one message is included in an RFC5444 packet, using a
single ICV Packet TLV or single TIMESTAMP Packet TLV is more
efficient than including ICV and TIMESTAMP Message TLVs in each
message created. If the RFC5444 multiplexer is capable of adding the
Packet TLVs, it SHOULD be instructed to include the Packet TLVs in
packets containing AODVv2 messages. However, if the multiplexer is
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not capable of adding the Packet TLVs, the TLVs MUST be included as
Message TLVs in each AODVv2 message in the packet.
After message generation, but before transmission, the ICV and
TIMESTAMP TLVs MUST be added according to each message type as
detailed in the following sections. The following steps list the
procedure to be performed:
1. If the TIMESTAMP is to be included, depending on AODVv2 message
type as specified below, add the TIMESTAMP TLV.
* When a TIMESTAMP Packet TLV is being added, the Packet TLV
Block size field MUST be updated.
* When a TIMESTAMP Message TLV is being added, the Message TLV
Block size field MUST be updated.
2. The considerations in Section 8 and section 9 of [RFC7182] are
followed, removing existing ICV TLVs and adjusting the size and
flags fields as appropriate:
* When an ICV Packet TLV is being added, existing ICV Packet
TLVs MUST be removed and the Packet TLV Block size MUST be
updated. If the Packet TLV Block now contains no TLVs, the
phastlv bit in the <pkt-flags> field in the Packet Header MUST
be cleared.
* When an ICV Message TLV is being added, existing ICV Message
TLVs are removed and the Message TLV Block Size MUST be
updated.
3. Mutable fields in the message must have their mutable values set
to zero before calculating the ICV.
* If the msg-hop-limit field is included in the [RFC5444]
message header, msg-hop-limit MUST be set to zero before
calculating the ICV.
* If a PATH_METRIC TLV is included, any values present in the
TLV MUST be set to zero before calculating the ICV value.
4. Depending on the message type, the ICV is calculated over the
appropriate fields (as specified in sections Section 11.1,
Section 11.2, Section 11.3 and Section 11.4) to include the
fields <hash-function>, <cryptographic-function>, <key-id-
length>, and, if present, <key-id> (in that order), followed by
the entire packet or message. This value MAY be truncated (as
specified in [RFC7182]).
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5. Add the ICV TLV, updating size fields as necessary.
6. The changes made in Step 2 and Step 3 are reversed to re-add any
existing ICV TLVs, re-adjust the relevant size and flags fields,
and set the msg-hop-limit and PATH_METRIC TLV values.
On message reception, and before message processing, verification of
the received message MUST take place:
1. The considerations in Section 8 and Section 9 of [RFC7182] are
followed, removing existing ICV TLVs and adjusting the size and
flags fields as appropriate.
* When verifying the ICV value in an ICV Packet TLV, all ICV
Packet TLVs present in the Packet TLV Block MUST be removed
before calculating the ICV, and the Packet TLV Block size MUST
be updated. If there are no remaining Packet TLVs, the Packet
TLV Block MUST be removed and the phastlv bit in the <pkt-
flags> field MUST be cleared.
* When verifying the ICV value in an ICV Message TLV, all ICV
Message TLVs present in the Message TLV Block MUST be removed
before calculating the ICV, and the Message TLV Block size
MUST be updated.
2. Mutable fields in the message MUST have their mutable values set
to zero before calculating the ICV.
* If the msg-hop-limit field is included in the [RFC5444]
message header, msg-hop-limit MUST be set to zero before
calculating the ICV.
* If a PATH_METRIC TLV is included, any values present in the
TLV MUST be set to zero before calculating the ICV value.
3. The ICV is calculated following the considerations in
Section 12.2 of [RFC7182], to include the fields <hash-function>,
<cryptographic-function>, <key-id-length>, and, if present, <key-
id> (in that order), followed by the entire packet or message.
* If the received ICV value is truncated, the calculated ICV
value MUST also be truncated (as specified in [RFC7182]),
before comparing.
* If the ICV value calculated from the received message or
packet does not match the value of <ICV-data> in the received
message or packet, the validation fails and the AODVv2 message
MUST be discarded and NOT processed or forwarded.
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* If the ICV values do match, the values set to zero before
calculating the ICV are reset to the received values, and
processing continues to Step 4.
4. Verification of a received TIMESTAMP value MUST be performed.
The procedure depends on message type as specified in the
following sub sections.
* If the TIMESTAMP value in the received message is not valid,
the AODVv2 message MUST be discarded and NOT processed or
forwarded.
* If the TIMESTAMP value is valid, processing continues as
defined in Section 7.
11.1. RREQ Generation and Reception
Since OrigPrefix is included in the RREQ, the ICV can be calculated
and verified using the [RFC5444] contents.The ICV TLV has type
extension := 1. Inclusion of an ICV TLV message integrity and
endpoint authentication, because trusted routers MUST hold the shared
key in order to calculate the ICV value, both to include when
creating a message, and to validate the message by checking that the
ICV is correct.
Since RREQ_Gen's sequence number is incremented for each new RREQ,
replay protection is already afforded and no extra TIMESTAMP TLV is
required.
After message generation and before message transmission:
1. Add the ICV TLV as described above.
On message reception and before message processing:
1. Verify the received ICV value as described above.
2. Verification of the sequence number is handled according to
Section 7.
11.2. RREP Generation and Reception
Since TargPrefix is included in the RREP, the ICV can be calculated
and verified using the [RFC5444] contents. The ICV TLV has type
extension 1. Inclusion of an ICV provides message integrity and
endpoint authentication, because trusted routers MUST hold a valid
key in order to calculate the ICV value, both to include when
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creating a message, and to validate the message by checking that the
ICV is correct.
Since RREP_Gen's sequence number is incremented for each new RREP,
replay protection is already afforded and no extra TIMESTAMP TLV is
required.
After message generation and before message transmission:
1. Add the ICV TLV as described above.
On message reception and before message processing:
1. Verify the received ICV value as described above.
2. Verification of the sequence number is handled according to
Section 7.
11.3. RREP_Ack Generation and Reception
Since no sequence number is included in the RREP_Ack, a TIMESTAMP TLV
MUST be included to protect against replay attacks. The value in the
TIMESTAMP TLV is set as follows:
o For RREP_Ack request, use Neighbor.AckSeqNum.
o For RREP_Ack response, use the sequence number from the TIMESTAMP
TLV in the received RREP_Ack request.
Since no addresses are included in the RREP_Ack, and the receiver of
the RREP_Ack uses the source IP address of a received RREP_Ack to
identify the sender, the ICV MUST be calculated using the message
contents and the IP source address. The ICV TLV has type extension
:= 2 in order to accomplish this. This provides message integrity
and endpoint authentication, because trusted routers MUST hold the
correct key in order to calculate the ICV value.
After message generation and before message transmission:
1. Add the TIMESTAMP TLV and ICV TLV as described above.
On message reception and before message processing:
1. Verify the received ICV value as described above.
2. Verify the received TIMESTAMP value by comparing the sequence
number in the value field of the TIMESTAMP TLV as follows:
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* For a received RREP_Ack request, there is no need to verify
the timestamp value. Proceed to message processing as defined
in Section 7.
* For a received RREP_Ack response, compare with the
Neighbor.AckSeqNum of the Neighbor Set entry for sender of the
RREP_Ack request.
* If the sequence number does not match, the AODVv2 message MUST
be discarded. Otherwise, Neighbor.AckSeqNum is incremented by
1 and processing continues according to Section 7.
11.4. RERR Generation and Reception
Since the sender's sequence number is not contained in the RERR, a
TIMESTAMP TLV MUST be included to protect against replay attacks.
The value in the TIMESTAMP TLV is set by incrementing and using
RERR_Gen's sequence number.
Since the receiver of the RERR MUST use the source IP address of the
RERR to identify the sender, the ICV MUST be calculated using the
message contents and the IP source address. The ICV TLV has type
extension := 2 in order to accomplish this. This provides message
integrity and endpoint authentication, because trusted routers MUST
hold the shared key in order to calculate the ICV value.
After message generation and before message transmission:
1. Add the TIMESTAMP TLV and ICV TLV as described above.
On message reception and before message processing:
1. Verify the received ICV value as described above.
2. Verify the received TIMESTAMP value by comparing the sequence
number in the value field of the TIMESTAMP TLV with the
Neighbor.HeardRERRSeqNum. If the sequence number in the message
is lower than the stored value, the AODVv2 message MUST be
discarded. Otherwise, the Neighbor.HeardRERRSeqNum MUST be set
to the received value and processing continues according to
Section 7.
12. Configuration
AODVv2 uses various parameters which can be grouped into the
following categories:
o Timers
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o Protocol constants
o Administrative parameters and controls
This section show the parameters along with their definitions and
default values (if any).
Note that several fields have limited size (bits or bytes). These
sizes and their encoding may place specific limitations on the values
that can be set.
12.1. Timers
AODVv2 requires certain timing information to be associated with
Local Route Set entries and message replies. The default values are
as follows:
+------------------------+----------------+
| Name | Default Value |
+------------------------+----------------+
| ACTIVE_INTERVAL | 5 second |
| MAX_IDLETIME | 200 seconds |
| MAX_BLACKLIST_TIME | 200 seconds |
| MAX_SEQNUM_LIFETIME | 300 seconds |
| RERR_TIMEOUT | 3 seconds |
| RteMsg_ENTRY_TIME | 12 seconds |
| RREQ_WAIT_TIME | 2 seconds |
| RREP_Ack_SENT_TIMEOUT | 1 second |
| RREQ_HOLDDOWN_TIME | 10 seconds |
+------------------------+----------------+
Table 2: Timing Parameter Values
The above timing parameter values have worked well for small and
medium well-connected networks with moderate topology changes. The
timing parameters SHOULD be administratively configurable. Ideally,
for networks with frequent topology changes the AODVv2 parameters
SHOULD be adjusted using experimentally determined values or dynamic
adaptation. For example, in networks with infrequent topology
changes MAX_IDLETIME MAY be set to a much larger value. If the
values were configured differently, the following consequences may be
observed:
o If MAX_SEQNUM_LIFETIME was configured differently across the
network, and any of the routers lost their sequence number or
rebooted, this could result in their next route messages being
classified as stale at any AODVv2 router using a greater value for
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MAX_SEQNUM_LIFETIME. This would delay route discovery from and to
the re-initializing router.
o Routers with lower values for ACTIVE_INTERVAL + MAX_IDLETIME will
invalidate routes more quickly and free resources used to maintain
them. This can affect bursty traffic flows which have quiet
periods longer than ACTIVE_INTERVAL + MAX_IDLETIME. A route which
has timed out due to perceived inactivity is not reported. When
the bursty traffic resumes, it would cause a RERR to be generated,
and the traffic itself would be dropped. This route would be
removed from all upstream routers, even if those upstream routers
had larger ACTIVE_INTERVAL or MAX_IDLETIME values. A new route
discovery would be required to re-establish the route, causing
extra routing protocol traffic and disturbance to the bursty
traffic.
o Routers with lower values for MAX_BLACKLIST_TIME would allow
neighboring routers to participate in route discovery sooner than
routers with higher values. This could result in failed route
discoveries if un-blacklisted links are still uni-directional.
Since RREQs are retried, this would not affect success of route
discovery unless this value was so small as to un-blacklist the
router before the RREQ is retried. This value need not be
consistent across the network since it is used for maintaining a
1-hop blacklist. However it MUST be greater than RREQ_WAIT_TIME;
the default value is much larger.
o Routers with lower values for RERR_TIMEOUT may create more RERR
messages than routers with higher values. This value should be
large enough that a RERR will reach all routers using the route
reported within it before the timer expires, so that no further
data traffic will arrive, and no duplicated RERR messages will be
generated.
o Routers with lower values for RteMsg_ENTRY_TIME may not consider
received redundant multicast route messages as redundant, and may
forward these messages unnecessarily.
o Routers with lower values for RREQ_WAIT_TIME may send more
frequent RREQ messages and wrongly determine that a route does not
exist, if the delay in receiving an RREP is greater than this
interval.
o Routers with lower values for RREP_Ack_SENT_TIMEOUT may wrongly
determine links to neighbors to be unidirectional if an RREP_Ack
is delayed longer than this timeout.
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o Routers with lower values for RREQ_HOLDDOWN_TIME will retry failed
route discoveries sooner than routers with higher values. This
may be an advantage if the network topology is frequently
changing, or may unnecessarily cause more routing protocol
traffic.
MAX_SEQNUM_LIFETIME MUST be configured to have the same values for
all AODVv2 routers in the network.
12.2. Protocol Constants
AODVv2 protocol constants typically do not require changes. The
following table lists these constants, along with their values and a
reference to the section describing their use.
+------------------------+-------------+----------------------------+
| Name | Default | Description |
+------------------------+-------------+----------------------------+
| DISCOVERY_ATTEMPTS_MAX | 3 | Section 6.6 |
| RREP_RETRIES | 2 | Section 7.2.1 |
| MAX_METRIC[MetricType] | [see below] | Section 5 |
| MAX_METRIC[HopCount] | 255 | Section 5 and Section 7 |
| MAX_HOPCOUNT | 20 | Limit to number of hops an |
| | | RREQ or RREP message can |
| | | traverse |
| INFINITY_TIME | [see below] | Maximum expressible clock |
| | | time (Section 6.7.2) |
+------------------------+-------------+----------------------------+
Table 3: AODVv2 Constants
MAX_HOPCOUNT cannot be larger than 255.
MAX_METRIC[MetricType] MUST always be the maximum expressible metric
value of type MetricType. Field lengths associated with metric
values are found in Section 13.4.
These protocol constants MUST have the same values for all AODVv2
routers in the ad hoc network. If the values were configured
differently, the following consequences may be observed:
o DISCOVERY_ATTEMPTS_MAX: Routers with higher values are likely to
be more successful at finding routes, at the cost of additional
control traffic.
o RREP_RETRIES: Routers with lower values are more likely to
blacklist neighbors when there is a temporary fluctuation in link
quality.
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o MAX_METRIC[MetricType]: No interoperability problems due to
variations on different routers, but routers with lower values may
exhibit overly restrictive behavior during route comparisons.
o MAX_HOPCOUNT: Routers with a value too small would not be able to
discover routes to distant addresses.
o INFINITY_TIME: No interoperability problems due to variations on
different routers, but if a lower value is used, route state
management may exhibit overly restrictive behavior.
12.3. Local Settings
The following table lists AODVv2 parameters which SHOULD be
administratively configured for each router:
+------------------------+---------------------------+--------------+
| Name | Default Value | Description |
+------------------------+---------------------------+--------------+
| Interface Set | | Section 4.1 |
| Router Client Set | | Section 4.2 |
| BUFFER_SIZE_PACKETS | 2 | Section 6.6 |
| BUFFER_SIZE_BYTES | MAX_PACKET_SIZE [TBD] | Section 6.6 |
| CONTROL_TRAFFIC_LIMIT | [Adjust for 10% capacity] | Section 7 |
+------------------------+---------------------------+--------------+
Table 4: Configuration for Local Settings
12.4. Network-Wide Settings
The following administrative controls MAY be used to change the
operation of the network. The same settings SHOULD be used across
the network. Inconsistent settings at different routers in the
network will not result in protocol errors.
+----------------------+-----------+----------------+
| Name | Default | Description |
+----------------------+-----------+----------------+
| ENABLE_IDLE_IN_RERR | Disabled | Section 7.4.1 |
+----------------------+-----------+----------------+
Table 5: Configuration for Network-Wide Settings
13. IANA Considerations
This section specifies several [RFC5444] message types and address
tlv-types required for AODVv2.
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13.1. RFC 5444 Message Type Allocation
This specification defines four Message Types, to be allocated from
the 0-223 range of the "Message Types" namespace defined in
[RFC5444].
+-----------------------------------------+-----------+
| Name of Message | Type |
+-----------------------------------------+-----------+
| Route Request (RREQ) | 10 (TBD) |
| Route Reply (RREP) | 11 (TBD) |
| Route Error (RERR) | 12 (TBD) |
| Route Reply Acknowledgement (RREP_Ack) | 13 (TBD) |
+-----------------------------------------+-----------+
13.2. RFC 5444 Message TLV Types
This specification defines one Message TLV Type, to be allocated from
the Message-Type-specific "Message TLV Types" namespace defined in
[RFC5444], as specified in Table 6.
+------------------------+----------+---------------+---------------+
| Name of TLV | Type | Length | Reference |
| | | (octets) | |
+------------------------+----------+---------------+---------------+
| ACK_REQ | 128 | 0 | Section 6.2 |
| | (TBD) | | |
+------------------------+----------+---------------+---------------+
Table 6: AODVv2 Message TLV Types
13.3. RFC 5444 Address Block TLV Type Allocation
This specification defines three Address Block TLV Types, to be
allocated from the Message-Type-specific "Address Block TLV Types"
namespace defined in [RFC5444], as specified in Table 7.
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+------------------------+----------+---------------+---------------+
| Name of TLV | Type | Length | Reference |
| | | (octets) | |
+------------------------+----------+---------------+---------------+
| PATH_METRIC | 129 | depends on | Section 7 |
| | (TBD) | MetricType | |
| SEQ_NUM | 130 | 2 | Section 7 |
| | (TBD) | | |
| ADDRESS_TYPE | 131 | 1 | Section 8 |
| | (TBD) | | |
+------------------------+----------+---------------+---------------+
Table 7: AODVv2 Address Block TLV Types
13.4. MetricType Allocation
The metric types used by AODVv2 are identified according to Table 8.
All implementations MUST use these values.
+---------------------+----------+--------------------+
| Name of MetricType | Type | Metric Value Size |
+---------------------+----------+--------------------+
| Unassigned | 0 | Undefined |
| Hop Count | 1 | 1 octet |
| Unallocated | 2 - 254 | TBD |
| Reserved | 255 | Undefined |
+---------------------+----------+--------------------+
Table 8: AODVv2 Metric Types
13.5. ADDRESS_TYPE TLV Values
These values are used in the [RFC5444] Address Type TLV discussed in
Section 8. All implementations MUST use these values.
+---------------+--------+
| Address Type | Value |
+---------------+--------+
| ORIGPREFIX | 0 |
| TARGPREFIX | 1 |
| UNREACHABLE | 2 |
| PKTSOURCE | 3 |
| UNSPECIFIED | 255 |
+---------------+--------+
Table 9: AODVv2 Address Types
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14. Security Considerations
This section describes various security considerations and potential
avenues to secure AODVv2 routing. The main objective of the AODVv2
protocol is for each router to communicate reachability information
about addresses for which it is responsible, and for routes it has
discovered from other AODVv2 routers.
Networks using AODVv2 to maintain connectivity and establish routes
on demand may be vulnerable to certain well-known types of threats,
which will be detailed in this section. Some of the threats
described can be mitigated or eliminated. Tools to do so will be
described.
With the exception of metric values, AODVv2 assures the integrity of
all RteMsg data end-to-end though the use of ICVs (see
Section 14.4.2. AODVv2 implementations support ICV and TIMESTAMP
TLVs, unless the implementation is intended for an environment in
which security is unnecessary; otherwise, AODVv2 deployments are
configured to use these TLVs to secure messages.
The on-demand nature of AODVv2 route discovery automatically reduces
the vulnerability to route disruption. Since control traffic for
updating route tables is diminished, there is less opportunity for
attack and failure.
14.1. Availability
Threats to AODVv2 which reduce availability are considered below.
14.1.1. Denial of Service
Flooding attacks using RREQ amount to a (BLIND) denial of service for
route discovery: By issuing RREQ messages for targets that don't
exist, an attacker can flood the network, blocking resources and
drowning out legitimate traffic. By triggering the generation of
CONTROL_TRAFFIC_LIMIT amount of messages (for example by sending
RREQs for many non-existent destinations), an attacker can prevent
legitimate messages from being generated. The effect of this attack
is dampened by the fact that duplicate RREQ messages are dropped
(preventing the network from DDoSing itself). Processing
requirements for AODVv2 messages are typically quite small, however
AODVv2 routers receiving RREQs do allocate resources in the form of
Neighbor Set, Local Route Set and Multicast Route Message Set
entries. The attacker can maximize their impact on set growth by
changing OrigPrefix or OrigPrefixLen for each RREQ. If a specific
node is to be targeted, this attack may be carried out in a
DISTRIBUTED fashion, either by compromising its direct neighbors or
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by specifying the target's address with TargPrefix and TargPrefixLen.
Note that it might be more economical for the attacker to simply jam
the medium; an attack which AODVv2 cannot defend itself against.
Mitigation:
o If AODVv2 routers always verify that the sender of the RERR
message is trusted, this threat is reduced. Processing
requirements would typically be dominated by calculations to
verify integrity. This has the effect of reducing (but by no
means eliminating) AODVv2's vulnerability to denial of service
attacks.
o Authentication of senders can prevent unauthenticated routers from
launching a Denial of Service attack on another AODVv2 router.
However, this does not protect the network if an attacker has
access to an already authenticated router.
14.1.2. Malicious RERR messages
RERR messages are designed to cause removal of installed routes. A
malicious node could send an RERR message with false information to
attempt to get other routers to remove a route to one or more
specific destinations, therefore disrupting traffic to the advertised
destinations.
Routes will be deleted if an RERR is received, withdrawing a route
for which the sender is the receiver's next hop, if both of the
following conditions are met:
o the RERR includes the MetricType of the installed route,
o the RERR includes either no sequence number for the route, or
includes a greater sequence number than the sequence number stored
with that route in the receiver's Local Route Set.
Routes will also be deleted if a received RERR contains a PktSource
address corresponding to a Router Client.
The information necessary to construct a malicious RERR could be
discovered by eavesdropping, either by listening to AODVv2 messages
or by watching data packet flows.
When the RERR is multicast, it can be received by many routers in the
ad hoc network, and will be regenerated when processing results in an
active route being removed. This threat could have serious impact on
applications communicating by way of the sender of the RERR message.
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o The set of routers which use the malicious router as a next hop
may be targeted with a malicious RERR with no PktSource address
included, if the RERR contains routes for which the malicious
router is a next hop from the receiving router. However, since
the sender of the RERR message is either malicious or broken, it
is better that it is not used as a next hop for these routes
anyway.
o A single router which does not use the malicious router as part of
its route may be targeted with a malicious RERR with a PktSource
address included.
o Replayed RERR messages could be used to disrupt active routes.
Mitigation:
o Protection against eavesdropping of AODVv2 messages would mitigate
this attack to some extent, but eavesdropping of data packets can
also be used to deduce the information about which routes could be
targeted.
o Protection against a malicious router becoming part of a route
will mitigate the attack where a set of routers are targeted.
This will not protect against the attack if a PktSource address is
included.
o By only regenerating RERR messages where active routes are
removed, the spread of the malicious RERR is limited.
o Including sequence numbers in RERR messages offers protection
against attacks using replays of these RERR messages.
o If AODVv2 routers always verify that the sender of the RERR
message is trusted, this threat is reduced.
14.1.3. False Confirmation of Link Bidirectionality
Links could be erroneously treated as bidirectional if malicious
unsolicited or spoofed RREP messages were to be accepted. This would
result in a route being installed which could not in fact be used to
forward data to the destination, and may divert data packets away
from the intended destination.
There is a window of RREQ_WAIT_TIME after an RREQ is sent, in which
any malicious router could send an RREP in response, in order for the
link to the malicious router to be deemed as bidirectional.
Mitigation:
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o Ignoring unsolicited RREP and RREP_Ack messages partially
mitigates against this threat.
o If AODVv2 routers always verify that the sender of the RREP
message is trusted, this threat is reduced.
14.1.4. Message Deletion
A malicious router could decide not to forward an RREQ or RREP or
RERR message. Not forwarding a RERR or RREP message would disrupt
route discovery. Not regenerating a RERR message would result in the
source of data packets continuing to maintain and use the route, and
further RERR messages being generated by the sender of the non-
regenerated RERR. A malicious router could intentionally disrupt
traffic flows by not allowing the source of data traffic to re-
discover a new route when one breaks.
Failing to send an RREP_Ack would also disrupt route establishment,
by not allowing the reverse route to be validated. Return traffic
which needs that route will prompt a new route discovery, wasting
resources and incurring a slight delay but not disrupting the ability
for applications to communicate.
Mitigation:
o None. Note that malicious router would have to wait for a route
to break before it could perform this attack.
14.2. Confidentiality
Passive inspection (eavesdropping) of AODVv2 control messages could
enable unauthorized devices to gain information about the network
topology, since exchanging such information is the main purpose of
AODVv2.
Eavesdropping of data traffic could allow a malicious device to
obtain information about how data traffic is being routed. With
knowledge of source and destination addresses, malicious messages
could be constructed to disrupt normal operation.
14.3. Integrity of Routes
Integrity of route information can be compromised in the following
types of attack:
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14.3.1. Message Insertion
Valid route set entries can be replaced or modified by maliciously
constructed AODVv2 messages, destroying existing routes and the
network's integrity. Any router may pose as another router by
sending RREQ, RREP, RREP_Ack and RERR messages in its name.
o Sending an RREQ message with false information can disrupt traffic
to OrigPrefix, if the sequence number attached is not stale
compared to any existing information about OrigPrefix. Since RREQ
is multicast and likely to be received by all routers in the ad
hoc network, this threat could have serious impact on applications
communicating with OrigPrefix.
o The actual threat to disrupt routes to OrigPrefix is reduced by
the AODVv2 mechanism of marking RREQ-derived routes as
"Unconfirmed" until the route to OrigAddr can be confirmed.
o Sending an RREP message with false information can disrupt traffic
to TargPrefix. Since RREP is unicast, and ignored if a
corresponding RREQ was not recently sent, this threat is
minimized, and is restricted to receivers along the path from
OrigAddr to TargAddr.
o Sending an RREP_Ack response message with false information can
cause the route to an originator address to be erroneously
accepted even though the route would contain a unidirectional link
and thus not be suitable for most traffic. Since the RREP_Ack
response is unicast, and ignored if an RREP_Ack was not sent
recently to the sender of this RREP_Ack response, this threat is
minimized and is strictly local to the RREP transmitter expecting
the acknowledgement. Unsolicited RREP_Acks are ignored.
o Sending an RERR message with false information is discussed in
Section 14.1.2.
Mitigation:
o If AODVv2 routers always verify that the sender of a message is
trusted, this threat is reduced.
14.3.2. Message Modification - Man in the Middle
Any AODVv2 router can forward messages with modified data.
Mitigation:
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o If AODVv2 routers verify the integrity of AODVv2 messages, then
the threat of disruption is minimized. A man in the middle with
no knowledge of the key used to calculate an integrity check value
may modify a message but the message will be rejected when it
fails an integrity check.
14.3.3. Replay Attacks
Replaying of RREQ or RREP messages would be of less use to an
attacker, since they would be dropped immediately due to their stale
sequence number. RERR messages may or may not include sequence
numbers and are therefore susceptible to replay attacks. RREP_Ack
messages do not include sequence numbers and are therefore
susceptible to replay attacks.
Mitigation:
o Use of timestamps or sequence numbers prevents replay attacks.
14.4. Protection Mechanisms
14.4.1. Confidentiality and Authentication
Encryption MAY be used for AODVv2 messages. If the routers share a
packet-level security association, the message data can be encrypted
prior to message transmission. The establishment of such security
associations is outside the scope of this specification. Encryption
will not only protect against unauthorized devices obtaining
information about network topology (eavesdropping) but will ensure
that only trusted routers participate in routing operations.
14.4.2. Message Integrity using ICVs
Cryptographic Integrity Check Values (ICVs) can be used to ensure
integrity of received messages, protecting against man in the middle
attacks. Further, by using ICVs, only those routers with knowledge
of a shared secret key are allowed to participate in routing
information exchanges. [RFC7182] defines ICV TLVs for use with
[RFC5444].
The data contained in AODVv2 routing protocol messages MUST be
verified using Integrity Check Values, to avoid accepting tampered
messages.
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14.4.3. Replay Protection using Timestamps
[RFC7182] defines a TIMESTAMP TLV for use with [RFC5444] which can be
used to prevent replay attacks when sequence numbers are not already
included.
The data contained in AODVv2 routing protocol messages can be
protected with a TIMESTAMP value to ensure the protection against
replaying of the message. Sequence numbers can be used in place of
timestamps, since they are known to be strictly increasing.
14.5. Key Management
The method of distribution of shared secret keys is out of the scope
of this protocol. Key management is not specified for the following
reasons:
Against [RFC4107], an analysis as to whether automated or manual key
management should be used shows a compelling case for automated
management. In particular:
o a potentially large number of routers may have to be managed,
belonging to several organisations, for example in vehicular
applications.
o a stream cipher is likely to be used, such as an AES variant.
o long term session keys might be used by more than two parties,
including multicast operations. AODVv2 makes extensive use of
multicast.
o there may be frequent turnover of devices.
On reviewing the case for manual key management against the same
document, it can be seen that manual management might be advantageous
in environments with limited bandwidth or high round trip times.
AODVv2 lends itself to sparse ad hoc networks where transmission
conditions may indeed be limited, depending on the bearers selected
for use.
However, [RFC4107] assumes that the connectivity between endpoints is
already available. In AODVv2, no route is available to a given
destination until a router client requests that user traffic be
transmitted. It is required to secure the signalling path of the
routing protocol that will establish the path across which key
exchange functions might subsequently be applied, which is clearly
the reverse of the expected functionality. A different strategy is
therefore required.
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There are two possible solutions. In each case, it is assumed that a
defence in depth security posture is being adopted by the system
integrator, such that each function in the network as a whole is
appropriately secured or defended as necessary, and that there is not
complete reliance on security mechanisms built in to AODVv2. Such
additional mechanisms could include a suitable wireless device
security technology, so that wireless devices are authenticated and
secured by their peers prior to exchanging user data, which in this
case would include AODVV2 signalling traffic as a payload, and
mechanisms which verify the authenticity and/or integrity of
application-layer user data transported once a route has been
established.
1. In the case that no AODVv2 routers have any detailed prior
knowledge of any other AODVv2 router, but does have knowledge of
the credentials of other organisations in which the router has
been previously configured to trust, it is possible for an AODVv2
router to send an initialisation vector as part of an exchange,
which could be verified against such credentials. Such an
exchange could make use of Identity-Based Signatures
([I-D.ietf-manet-ibs]), based on Elliptic Curve-Based
Certificateless Signatures for Identity-Based Encryption
[RFC6507], which eliminate the need for a handshake process to
establish trust.
2. If it is impossible to use Identity-Based Signatures, and the
risk to the AODVv2 signalling traffic is considered to be low due
to the use of security countermeasures elsewhere in the system, a
simple pre-placed shared secret could be used between routers,
which is used as-is or is used to generate some ephemeral secret
based on another known variable, such as time of day if that is
universally available at a level of accuracy sufficient to make
such a system viable.
15. Acknowledgments
AODVv2 is a descendant of the design of previous MANET on-demand
protocols, especially AODV [RFC3561] and DSR [RFC4728]. Changes to
previous MANET on-demand protocols stem from research and
implementation experiences. Thanks to Elizabeth Belding and Ian
Chakeres for their long time authorship of AODV. Additional thanks
to Derek Atkins, Emmanuel Baccelli, Abdussalam Baryun, Ramon Caceres,
Justin Dean, Christopher Dearlove, Fatemeh Ghassemi, Ulrich Herberg,
Henner Jakob, Ramtin Khosravi, Luke Klein-Berndt, Lars Kristensen,
Tronje Krop, Koojana Kuladinithi, Kedar Namjoshi, Keyur Patel,
Alexandru Petrescu, Henning Rogge, Fransisco Ros, Pedro Ruiz,
Christoph Sommer, Romain Thouvenin, Richard Trefler, Jiazi Yi, Seung
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Yi, Behnaz Yousefi, and Cong Yuan, for their reviews of AODVv2 and
DYMO, as well as numerous specification suggestions.
16. References
16.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
[RFC3561] Perkins, C., Belding-Royer, E., and S. Das, "Ad hoc On-
Demand Distance Vector (AODV) Routing", RFC 3561,
DOI 10.17487/RFC3561, July 2003,
<http://www.rfc-editor.org/info/rfc3561>.
[RFC5444] Clausen, T., Dearlove, C., Dean, J., and C. Adjih,
"Generalized Mobile Ad Hoc Network (MANET) Packet/Message
Format", RFC 5444, DOI 10.17487/RFC5444, February 2009,
<http://www.rfc-editor.org/info/rfc5444>.
[RFC5498] Chakeres, I., "IANA Allocations for Mobile Ad Hoc Network
(MANET) Protocols", RFC 5498, DOI 10.17487/RFC5498, March
2009, <http://www.rfc-editor.org/info/rfc5498>.
[RFC7182] Herberg, U., Clausen, T., and C. Dearlove, "Integrity
Check Value and Timestamp TLV Definitions for Mobile Ad
Hoc Networks (MANETs)", RFC 7182, DOI 10.17487/RFC7182,
April 2014, <http://www.rfc-editor.org/info/rfc7182>.
16.2. Informative References
[I-D.ietf-manet-ibs]
Dearlove, C., "Identity-Based Signatures for MANET Routing
Protocols", draft-ietf-manet-ibs-05 (work in progress),
March 2016.
[Koodli01]
Koodli, R. and C. Perkins, "Fast handovers and context
transfers in mobile networks", Proceedings of the ACM
SIGCOMM Computer Communication Review 2001, Volume 31
Issue 5, 37-47, October 2001.
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[Perkins94]
Perkins, C. and P. Bhagwat, "Highly Dynamic Destination-
Sequenced Distance-Vector Routing (DSDV) for Mobile
Computers", Proceedings of the ACM SIGCOMM '94 Conference
on Communications Architectures, Protocols and
Applications, London, UK, pp. 234-244, August 1994.
[RFC2501] Corson, S. and J. Macker, "Mobile Ad hoc Networking
(MANET): Routing Protocol Performance Issues and
Evaluation Considerations", RFC 2501,
DOI 10.17487/RFC2501, January 1999,
<http://www.rfc-editor.org/info/rfc2501>.
[RFC4107] Bellovin, S. and R. Housley, "Guidelines for Cryptographic
Key Management", BCP 107, RFC 4107, DOI 10.17487/RFC4107,
June 2005, <http://www.rfc-editor.org/info/rfc4107>.
[RFC4193] Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast
Addresses", RFC 4193, DOI 10.17487/RFC4193, October 2005,
<http://www.rfc-editor.org/info/rfc4193>.
[RFC4728] Johnson, D., Hu, Y., and D. Maltz, "The Dynamic Source
Routing Protocol (DSR) for Mobile Ad Hoc Networks for
IPv4", RFC 4728, DOI 10.17487/RFC4728, February 2007,
<http://www.rfc-editor.org/info/rfc4728>.
[RFC6130] Clausen, T., Dearlove, C., and J. Dean, "Mobile Ad Hoc
Network (MANET) Neighborhood Discovery Protocol (NHDP)",
RFC 6130, DOI 10.17487/RFC6130, April 2011,
<http://www.rfc-editor.org/info/rfc6130>.
[RFC6507] Groves, M., "Elliptic Curve-Based Certificateless
Signatures for Identity-Based Encryption (ECCSI)",
RFC 6507, DOI 10.17487/RFC6507, February 2012,
<http://www.rfc-editor.org/info/rfc6507>.
Appendix A. AODVv2 Draft Updates
This section lists the changes between AODVv2 revisions ...-16.txt
and ...-17.txt.
o Removed wording that suggested RREP_Gen could add multiple
(unrelated) subnets.
o Changed wording in accordance with decision to pursue Proposed
Standard.
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o Resolved an error scenario that was based on confirming routes to
OrigAddr before the route to OrigAddr was known to be operational.
But, another AODVv2 router closer to OrigAddr might forward
packets along a previously confirmed route with an obsolete
Sequence Number. These two conditions together were found to
allow for routing loops.
o Enabled multihoming by creating new address type SeqNoRtr, along
with rules prohibiting comparison of sequence numbers from
distinct multihoming routers per advertised prefix.
Authors' Addresses
Charles E. Perkins
Futurewei Inc.
2330 Central Expressway
Santa Clara, CA 95050
USA
Phone: +1-408-330-4586
Email: charliep@computer.org
Stan Ratliff
Idirect
13861 Sunrise Valley Drive, Suite 300
Herndon, VA 20171
USA
Email: ratliffstan@gmail.com
John Dowdell
Airbus Defence and Space
Celtic Springs
Newport, Wales NP10 8FZ
United Kingdom
Email: john.dowdell@airbus.com
Lotte Steenbrink
HAW Hamburg, Dept. Informatik
Berliner Tor 7
D-20099 Hamburg
Germany
Email: lotte.steenbrink@haw-hamburg.de
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Victoria Mercieca
Airbus Defence and Space
Celtic Springs
Newport, Wales NP10 8FZ
United Kingdom
Email: victoria.mercieca@airbus.com
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