Dynamic MANET On-demand (AODVv2) Routing
draft-ietf-manet-dymo-24
The information below is for an old version of the document.
| Document | Type |
This is an older version of an Internet-Draft whose latest revision state is "Replaced".
|
|
|---|---|---|---|
| Authors | Charles E. Perkins , Ian Chakeres | ||
| Last updated | 2012-11-30 | ||
| Replaced by | draft-ietf-manet-aodvv2, draft-ietf-manet-aodvv2, draft-ietf-manet-aodvv2, draft-ietf-manet-aodvv2 | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
| Formats | |||
| Reviews | |||
| Additional resources | Mailing list discussion | ||
| Stream | WG state | WG Document | |
| Document shepherd | (None) | ||
| IESG | IESG state | I-D Exists | |
| Consensus boilerplate | Unknown | ||
| Telechat date | (None) | ||
| Responsible AD | (None) | ||
| Send notices to | (None) |
draft-ietf-manet-dymo-24
Mobile Ad hoc Networks Working Group C. Perkins
Internet-Draft Futurewei
Intended status: Standards Track I. Chakeres
Expires: June 4, 2013 CenGen
December 1, 2012
Dynamic MANET On-demand (AODVv2) Routing
draft-ietf-manet-dymo-24
Abstract
The Dynamic MANET On-demand (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, offering on-demand convergence in dynamic
topologies.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on June 4, 2013.
Copyright Notice
Copyright (c) 2012 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
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
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described in the Simplified BSD License.
Table of Contents
1. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Notational Conventions . . . . . . . . . . . . . . . . . . . . 7
4. Applicability Statement . . . . . . . . . . . . . . . . . . . 9
5. Data Structures . . . . . . . . . . . . . . . . . . . . . . . 10
5.1. Route Table Entry . . . . . . . . . . . . . . . . . . . . 10
5.2. Bidirectional Connectivity During Route Discovery and
Blacklists . . . . . . . . . . . . . . . . . . . . . . . . 12
5.3. Router Clients and Client Networks . . . . . . . . . . . . 13
5.4. AODVv2 Packet Header Fields and Information Elements . . . 13
5.5. AODVv2 Sequence Numbers . . . . . . . . . . . . . . . . . 14
5.6. Enabling Alternate Metrics . . . . . . . . . . . . . . . . 15
6. AODVv2 Operations on Route Table Entries . . . . . . . . . . . 17
6.1. Evaluating Incoming Routing Information . . . . . . . . . 17
6.2. Applying Route Updates To Route Table Entries . . . . . . 19
6.3. Route Table Entry Timeouts . . . . . . . . . . . . . . . . 19
7. Routing Messages RREQ and RREP (RteMsgs) . . . . . . . . . . . 20
7.1. Route Discovery Retries and Buffering . . . . . . . . . . 20
7.2. RteMsg Structure . . . . . . . . . . . . . . . . . . . . . 21
7.3. RREQ Generation . . . . . . . . . . . . . . . . . . . . . 23
7.4. RREP Generation . . . . . . . . . . . . . . . . . . . . . 24
7.5. Handling a Received RteMsg . . . . . . . . . . . . . . . . 25
7.5.1. Additional Handling for Outgoing RREQ . . . . . . . . 26
7.5.2. Additional Handling for Outgoing RREP . . . . . . . . 27
8. Route Maintenance . . . . . . . . . . . . . . . . . . . . . . 27
8.1. Handling Route Lifetimes During Packet Forwarding . . . . 27
8.2. Active Next-hop Router Adjacency Monitoring . . . . . . . 28
8.3. RERR Generation . . . . . . . . . . . . . . . . . . . . . 28
8.3.1. Case 1: Undeliverable Packet . . . . . . . . . . . . . 29
8.3.2. Case 2: Broken Link . . . . . . . . . . . . . . . . . 30
8.4. Receiving and Handling RERR Messages . . . . . . . . . . . 30
9. Unknown Message and TLV Types . . . . . . . . . . . . . . . . 31
10. Simple Internet Attachment . . . . . . . . . . . . . . . . . . 32
11. Multiple Interfaces . . . . . . . . . . . . . . . . . . . . . 33
12. AODVv2 Control Packet/Message Generation Limits . . . . . . . 33
13. Optional Features . . . . . . . . . . . . . . . . . . . . . . 33
13.1. Expanding Rings Multicast . . . . . . . . . . . . . . . . 34
13.2. Intermediate RREP . . . . . . . . . . . . . . . . . . . . 34
13.3. Precursor Lists and Notifications . . . . . . . . . . . . 34
13.3.1. Overview . . . . . . . . . . . . . . . . . . . . . . . 34
13.3.2. Precursor Notification Details . . . . . . . . . . . . 35
13.4. Multicast RREP Response to RREQ . . . . . . . . . . . . . 35
13.5. RREP_ACK . . . . . . . . . . . . . . . . . . . . . . . . . 36
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13.6. Message Aggregation . . . . . . . . . . . . . . . . . . . 36
13.7. Added Routing Information in RteMsgs . . . . . . . . . . . 36
13.7.1. Including Added Node Information . . . . . . . . . . . 36
13.7.2. Handling Added Node Information . . . . . . . . . . . 37
14. Administratively Configured Parameters and Timer Values . . . 38
15. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 41
15.1. AODVv2 Message Types Specification . . . . . . . . . . . . 41
15.2. Message and Address Block TLV Type Specification . . . . . 41
15.3. Address Block TLV Specification . . . . . . . . . . . . . 42
15.4. Metric Type Number Allocation . . . . . . . . . . . . . . 42
16. Security Considerations . . . . . . . . . . . . . . . . . . . 43
17. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 45
18. References . . . . . . . . . . . . . . . . . . . . . . . . . . 45
18.1. Normative References . . . . . . . . . . . . . . . . . . . 45
18.2. Informative References . . . . . . . . . . . . . . . . . . 46
Appendix A. Example RFC 5444-compliant packet formats . . . . . . 47
A.1. RREQ Message Format . . . . . . . . . . . . . . . . . . . 48
A.2. RREP Message Format . . . . . . . . . . . . . . . . . . . 48
A.3. RERR Message Format . . . . . . . . . . . . . . . . . . . 49
A.4. RREP_ACK Message Format . . . . . . . . . . . . . . . . . 50
Appendix B. Changes since revision ...-21.txt . . . . . . . . . . 50
Appendix C. Shifting Network Prefix Advertisement Between
AODVv2 Routers . . . . . . . . . . . . . . . . . . . 53
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 53
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1. Overview
The Dynamic MANET On-demand (AODVv2) routing protocol [formerly named
DYMO] enables on-demand, multihop unicast routing among AODVv2
routers in mobile ad hod networks [MANETs][RFC2501]. The basic
operations of the AODVv2 protocol are route discovery and route
maintenance. Route discovery is performed when an AODVv2 router must
transmit a packet towards a destination for which it does not have a
route. Route maintenance is performed to avoid prematurely expunging
routes from the route table, and to avoid dropping packets when a
route being used to forward packets from the source to a destination
breaks.
During route discovery, an AODVv2 router multicasts a Route Request
message (RREQ) to find a route toward a particular destination, via
the AODVv2 router responsible for this destination. Using a hop-by-
hop retransmission algorithm, each intermediate AODVv2 router
receiving the RREQ message records a route toward the originator.
When the target's AODVv2 router (TargRtr) receives the RREQ, it
records a route toward the originator and responds with a Route Reply
(RREP) unicast hop-by-hop toward the originating AODVv2 router. Each
intermediate AODVv2 router that receives the RREP creates a route
toward the target, and unicasts the RREP hop-by-hop toward the
originator. When the originator's AODVv2 router receives the RREP,
routes have then been established between the originating AODVv2
router and the target AODVv2 router in both directions.
Route maintenance consists of two operations. In order to preserve
active routes, AODVv2 routers extend route lifetimes upon
successfully forwarding a packet. When a data packet is received for
forwarding and there is no valid route for the destination, then the
AODVv2 router of the source of the packet is notified via a Route
Error (RERR) message. Each upstream router that receives the RERR
marks the route as broken. Before such an upstream AODVv2 router
could forward a packet to the same destination, it would have to
perform route discovery again for that destination.
AODVv2 uses sequence numbers to assure loop freedom [Perkins99],
similarly to AODV. Sequence numbers enable AODVv2 routers to
determine the temporal order of AODVv2 route discovery messages,
thereby avoiding use of stale routing information. Unlike AODV,
AODVv2 uses RFC 5444 message and TLV formats.
2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
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"OPTIONAL" in this document are to be interpreted as described in
[RFC2119].
This document also uses some terminology from [RFC5444].
This document defines the following terminology:
Adjacency
A bi-directional relationship between neighboring routers for the
purpose of exchanging routing information. Not every pair of
neighboring routers will necessarily form an adjacency.
Neighboring routers may form an adjacency based on various
information or other protocols; for example, exchange of AODVv2
routing messages, other protocols (e.g. NDP [RFC4861] or NHDP
[RFC6130]), or manual configuration. Loss of a routing adjacency
may also be based upon similar information; monitoring of
adjacencies where packets are being forwarded is required (see
Section 8.2).
AODVv2 Router
An IP addressable device in the ad-hoc network that performs the
AODVv2 protocol operations specified in this document.
AODVv2 Sequence Number (SeqNum)
An AODVv2 Sequence Number is an unsigned integer maintained by
each AODVv2 router. This sequence number guarantees the temporal
order of routing information to maintain loop-free routes. The
value zero (0) is reserved to indicate that the SeqNum for a
destination address is unknown.
Current_Time
The current time as maintained by the AODVv2 router.
disregard
Ignore for further processing (see Section 5.4), and delete unless
it is required to keep the message in the packet for purposes of
authentication.
Handling Router (HandlingRtr)
HandlingRtr denotes the AODVv2 router handling an AODVv2 message.
Incoming Link
A link over which an AODVv2 has received a message from one of its
adjacent routers.
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MANET
A Mobile Ad Hoc Network as defined in [RFC2501].
node
An IP addressable device in the ad-hoc network. A node may be an
AODVv2 router, or it may be a device in the network that does not
perform any AODVv2 protocol operations. All nodes in this
document are either AODVv2 Routers or else Router Clients.
Originating Node (OrigNode)
The Originating Node is the node that launched the application
requiring communication with the Target Node. If OrigNode is not
itself an AODVv2 router, its AODVv2 router (OrigRtr) has the
responsibility to generate a AODVv2 RREQ message on behalf of
OrigNode when necessary to multicast a route discovery message.
Originating Router (OrigRtr)
The Originating Router is the AODVv2 router that serves OrigNode.
OrigRtr generates the RREQ message to discover a route for
TargNode.
reactive
A protocol operation is said to be "reactive" if it is performed
only in reaction to specific events. As used in this document,
"reactive" is essentially synonymous with "on-demand".
Routable Unicast IP Address
A routable unicast IP address is a unicast IP address that when
put into the IP.DestinationAddress field is scoped sufficiently to
be forwarded by a router. Globally-scoped unicast IP addresses
and Unique Local Addresses (ULAs) [RFC6549] are examples of
routable unicast IP addresses.
Route Error (RERR)
A RERR message is used to indicate that an AODVv2 router does not
have a route toward one or more particular destinations.
Route Reply (RREP)
A RREP message is used to establish a route between the RREQ
TargetNode and OrigNode, at all the AODVv2 routers between them.
Route Request (RREQ)
An AODVv2 router uses a RREQ message to discover a valid route to
a particular destination address, called the RREQ TargetNode. An
AODVv2 router processing a RREQ receives routing information for
the RREQ OrigNode.
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Router Client
An AODVv2 router may be configured with a list of other IP
addresses and networks which correspond to other non-router nodes
which require the services of the AODVv2 router for route
discovery and maintenance. An AODVv2 is always its own client, so
that the list of client IP addresses is never empty.
Sequence Number (SeqNum)
Same as AODVv2 Sequence Number.
Target Node (TargNode)
The Target Node denotes the node for which a route is needed.
Target Router (TargRtr)
The TargetRtr denotes the AODVv2 router which serves TargNode.
Type-Length-Value structure (TLV)
A generic way to represent information as specified in [RFC5444].
Unreachable Node (UnreachableNode)
An UnreachableNode is a node for which a forwarding route is
unknown.
valid route
A route that can be used for forwarding; in other words a route
that is not Broken or Expired.
3. Notational Conventions
This document uses the conventions found in Table 1 to describe
information in the fields from [RFC5444].
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+--------------------+-------------------------------------------+
| Notation | Information Location and/or Meaning |
+--------------------+-------------------------------------------+
| Route[DestAddr] | A route table entry towards DestAddr |
| Route[Addr]{field} | A field in a route table entry |
| -- | -- |
| RREQ.{field} | Field in RREQ |
| RREP.{field} | Field in RREP |
| RERR.{field} | Field in RERR |
| -- | -- |
| MsgHdr | the RFC5444 Message Header |
| MsgTLV | an RFC5444 Message TLV |
| MetricTypeTLV | MetricType MsgTLV for Metric AddrTLV |
| MAL | MsgHdr.<msg-addr-length> |
| -- | -- |
| AddrBlk | an RFC5444 address block |
| AddrBlk[1] | The first address slot in AddrBlk |
| AddrBlk[N] | The Nth address slot in AddrBlk |
| AddrBlk[OrigNode] | AddrBlk[1] |
| AddrBlk[TargNode] | AddrBlk[2] |
| AddrTLV | an RFC5444 address block TLV |
| AddrTLV[1] | the first item in AddrTLV |
| AddrTLV[N] | the Nth item in AddrTLV |
| AddrTLV[OrigNode] | AddrTLV[1] |
| AddrTLV[TargNode] | AddrTLV[2] |
| HopCountTLV | Metric8 AddrTLV when MetricTypeTLV=3 |
| Metric8TLV | Metric8 AddrTLV |
| SeqNumTLV | Sequence Number TLV for AddrBlk addresses |
| RteAddrBlk | the main address block in a RteMsg |
| RteSeqNumTLV | Sequence Numbers for RteAddrBlk addresses |
| UnreachAddrBlk | Unreachable Node AddrBlk in RERR |
| -- | -- |
| OrigRtr | RREQ Originating Router |
| OrigNode | Originating Node |
| RREQ_Gen | AODVv2 router originating an RREQ |
| RREP_Gen | AODVv2 router responding to an RREQ |
| RteMsg | either RREQ or RREP |
| RteMsg_Orig | Originator of a RteMsg |
| HandlingRtr | Handling Router |
| TargRtr | Target Router |
| TargNode | Target Node |
| UnreachableNode | Unreachable Node |
+--------------------+-------------------------------------------+
Table 1
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4. Applicability Statement
The AODVv2 routing protocol is designed for stub (i.e., non-transit)
or disconnected (i.e., from the Internet) mobile ad hoc networks
(MANETs). AODVv2 handles a wide variety of mobility patterns by
determining routes on-demand. AODVv2 also handles a wide variety of
traffic patterns. In networks with a large number of routers, AODVv2
is best suited for relatively sparse traffic scenarios where any
particular router forwards packets to only a small percentage of the
AODVv2 routers in the network, due to the on-demand nature of route
discovery and route maintenance.
Although AODVv2 is closely related to AODV [RFC3561], and has some of
the features of DSR [RFC4728], AODVv2 is not interoperable with
either of those other two protocols.
AODVv2 is applicable to memory constrained devices, since little
routing state is maintained in each AODVv2 router. Only routing
information related to routes between active sources and destinations
is maintained, in contrast to proactive routing protocols that
require routing information to all routers within the MANET be
maintained.
AODVv2 supports routers with multiple interfaces, as long as each
interface has its own IP address. In addition to routing for their
local processes, AODVv2 routers can also route on behalf of other
non-routing nodes (i.e., "hosts", or, in this document, "clients"),
reachable via those interfaces. Any such node which is not itself an
AODVv2 router SHOULD NOT be served by more than one AODVv2 router.
Multi-homing is difficult unless the sequence number is expanded to
include the IP address as well as OwnSeqNum. Otherwise, comparing
sequence numbers would not work to evaluate freshness. Even when the
IP address is included, there isn't a good way to compare sequence
numbers from different IP addresses, but at least a handling node can
determine whether the two given sequence numbers are comparable. If
the route table can store multiple routes for the same destination,
then multi-homing can work with sequence numbers augmented by IP
addresses.
AODVv2 routers perform route discovery to find a route toward a
particular destination. Therefore, AODVv2 routers MUST must be
configured to respond to RREQs for a certain set of addresses. When
AODVv2 is the only protocol interacting with the forwarding table,
AODVv2 MAY be configured to perform route discovery for all unknown
unicast destinations.
At all times within an AODVv2 MANET, only one AODVv2 router SHOULD be
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serve any particular routing client. The coordination among multiple
AODVv2 routers to distribute routing information correctly for a
shared address (i.e. an address that is advertised and can be reached
via multiple AODVv2 routers) is not described in this document. The
AODVv2 router operation of shifting responsibility for a routing
client from one AODVv2 router to another is mentioned in Appendix C.
Each AODVv2 router, if serving router clients other than itself, is
configured with information about the IP addresses of its clients.
No AODVv2 router is required to have information about the
relationship between any other AODVv2 router and its router clients.
Address assignment procedures are entirely out of scope for AODVv2.
AODVv2 only utilizes bidirectional links. In the case of possible
unidirectional links, either blacklists (see Section 5.2) or other
means (e.g. adjacency establishment with only neighboring routers
that have bidirectional communication as indicated by NHDP [RFC6130])
of assuring and monitoring bi-directionality is recommended.
Otherwise, persistent packet loss or persistent protocol failures
could occur. The Cost(L) of bidirectional link L may depend upon the
direction across the link for which the cost is measured.
The routing algorithm in AODVv2 may be operated at layers other than
the network layer, using layer-appropriate addresses. The routing
algorithm makes of some persistent state; if there is no persistent
storage available for this state, recovery can impose a performance
penalty in case of AODVv2 router reboots.
5. Data Structures
5.1. Route Table Entry
The route table entry is a conceptual data structure.
Implementations may use any internal representation so long as it
provides access to the same information as specified below.
Conceptually, a route table entry has the following fields:
Route.Address
The (host or network) destination address of the node(s)
associated with the routing table entry
Route.PfxLen
The value is the length of the netmask/prefix. If the value of
the Route.PfxLen is nonzero and different than the length of
addresses in the address family used by the AODVv2 routers, the
associated address is a routing prefix, rather than a host
address.
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Route.SeqNum
The AODVv2 SeqNum associated with a route table entry
Route.NextHopAddress
An IP address of the adjacent AODVv2 router on the path toward the
Route.Address
Route.NextHopInterface
The interface used to send packets toward the Route.Address
Route.LastUsed
The time that this route was last used
Route.ExpirationTime
The time at which this route must expire
Route.Broken
A flag indicating whether this Route is broken. This flag is set
to true if the next-hop becomes unreachable or in response to
processing to a RERR (see Section 8.4)
Route.MetricType
The type of the metric for the route towards Route.Address
Route.Metric
The cost of the route towards Route.Address
A route table entry (i.e., a route) may be in one of the following
states:
Active
An Active route is in current use for forwarding packets
Idle
An Idle route can be used for forwarding packets, even though it
is not in current use
Expired
After a route has been idle for too long, it expires, and may no
longer be used for forwarding packets
Broken
A route marked as Broken cannot be used for forwarding packets but
still has valid destination sequence number information.
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Timed
The expiration of a Timed route is controlled by the
Route.ExpirationTime time of the route table entry, not
MAX_IDLETIME. Until that time, a Timed route can be used for
forwarding packets. Afterwards, the route must be Expired (or
expunged).
The route's state determines the operations that can be performed on
the route table entry. During use, an Active route is maintained
continuously by AODVv2 and is considered to remain active as long as
it is used at least once during every ACTIVE_INTERVAL. When a route
is no longer Active, it becomes an Idle route. After a route remains
Idle for MAX_IDLETIME, it becomes an Expired route; after that, the
route is not used for forwarding, but the sequence number information
can be maintained until the destination sequence number has had no
updates for MAX_SEQNUM_LIFETIME. After MAX_SEQNUM_LIFETIME, old
sequence number information is considered no longer valuable and the
route is expunged.
MAX_SEQNUM_LIFETIME is the time after a reboot during which an AODVv2
router MUST NOT transmit any routing messages. Thus, if all other
AODVv2 routers expunge routes to the rebooted router after that time
interval, the rebooted AODVv2 router's sequence number will not be
considered stale by any other AODVv2 router in the MANET.
When the link to a route's next hop is broken, the route is marked as
being Broken, and the route may no longer be used.
5.2. Bidirectional Connectivity During Route Discovery and Blacklists
To avoid repeated failure of Route Discovery, an AODVv2 router
(HandlingRtr) handling a RREP message MAY attempt to verify
connectivity to the next upstream router towards AODVv2 router
originating an RREQ message, by including the Unicast Response
Request message TLV (see Section 15.2) in the RREP. Any unicast
packet will satisfy the Response Request, for example an ICMP REPLY
message. If the verification fails, HandlingRtr SHOULD put the
upstream neighbor in a blacklist. RREQs received from a blacklisted
node SHOULD NOT be retransmitted by HandlingRtr. However, the
upstream neighbor should not be permanently blacklisted; after a
certain time (MAX_BLACKLIST_TIME), it should once again be considered
as a viable upstream neighbor for route discovery operations.
For this purpose, a list of blacklisted nodes along with their time
of removal should be maintained:
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BlacklistNode
The IP address of the node that did not verify bidirectional
connectivity.
BlacklistRmTime
The time at which BlacklistNode will be removed from the
blacklist.
5.3. Router Clients and Client Networks
An AODVv2 router may offer routing services to other nodes that are
not AODVv2 routers. The AODVv2 Sequence Number is (by definition)
the same for the AODVv2 router and each of its clients.
For this purpose, a list of IP addresses nodes along with relevant
prefixes must be configured on each AODVv2:
Client IP address
The IP address of the node that requires routing service from the
AODVv2 router.
Client Prefix Length
The length of the routing prefix associated with the client IP
address.
If the Client Prefix Length is not the full length of the Client IP
address, then the prefix defines a Client Network. If an AODVv2
router is configured to serve a Client Network, then the AODVv2
router MUST serve every node that has an address within the range
defined by the routing prefix of the Client Network. The list of
Routing Clients for an AODVv2 router is never empty, since an AODVv2
router is always its own client as well.
5.4. AODVv2 Packet Header Fields and Information Elements
In its default mode of operation, AODVv2 uses the UDP port 269
[RFC5498] to carry protocol packets. In addition, IP Protocol Number
138 has been reserved for MANET protocols [RFC5498]. Most AODVv2
messages are sent with the IP destination address set to the link-
local multicast address LL-MANET-Routers [RFC5498] unless otherwise
specified. Therefore, all AODVv2 routers MUST subscribe to LL-MANET-
Routers [RFC5498] to receiving AODVv2 messages. In order to reduce
multicast overhead, retransmitting multicast packets in MANETs SHOULD
be done according to methods specified in [RFC6621]. AODVv2 does not
specify which method should be used to restrict the set of AODVv2
routers that have the responsibility to retransmit multicast packets.
Note that multicast packets MAY be sent via unicast. For example,
this may occur for certain link-types (non-broadcast media), for
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manually configured router adjacencies, or in order to improve
robustness.
The IPv4 TTL (IPv6 Hop Limit) field for all packets containing AODVv2
messages is set to 255. If a packet is received with a value other
than 255, any AODVv2 message contained in the packet MUST be
disregarded by AODVv2. This mechanism, known as "The Generalized TTL
Security Mechanism" (GTSM) [RFC5082] helps to assure that packets
have not traversed any intermediate routers.
IP packets containing AODVv2 protocol messages SHOULD be given
priority queuing and channel access.
AODVv2 messages are transmitted in packets that conform to the packet
and message format described in [RFC5444]. Here is a brief
description of the format.
A packet formatted according to RFC5444 contains zero or more
messages.
A message contains a message header, message TLV block, and zero
or more address blocks.
Each address block may also have associated TLV blocks.
If a packet contains only a single AODVv2 message and no packet TLVs,
it need not include a packet-header [RFC5444]. The length of an
address (32 bits for IPv4 and 128 bits for IPv6) inside an AODVv2
message is indicated by the msg-addr-length (MAL) in the msg-header,
as specified in [RFC5444].
When multiple messages are aggregated into a single packet according
to RFC 5444 formatting, and the aggregation of messages is also
authenticated (e.g., with IPsec), it becomes unfeasible to delete
individual messages. In such cases, instead of deleting individual
messages, they are maintained in the aggregation of messages, but
simply ignored for further processing. In such cases where
individual messages cannot be deleted, in this document "disregarded"
means "ignored". Otherwise, any such "disregarded" AODVv2 messages
SHOULD be deleted from the aggregated messages in the RFC 5444
packet.
5.5. AODVv2 Sequence Numbers
AODVv2 sequence numbers allow AODVv2 routers to evaluate the
freshness of routing information. Proper maintenance of sequence
numbers assures that the destination sequence number value stored by
intermediate AODVv2 routers is monotonically increasing along any
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path from any source to the destination. As a consequence, loop
freedom is assured.
Each AODVv2 router in the network MUST maintain its own sequence
number (OwnSeqNum, a 16-bit unsigned integer). An AODVv2 router
increments its OwnSeqNum as follows. Most of the time, OwnSeqNum is
incremented by simply adding one (1). But to increment OwnSeqNum
when it has the value of the largest largest possible number
representable as a 16-bit unsigned integer (i.e., 65,535), it MUST be
set to one (1). In other words, the sequence number after 65,535 is
1.
An AODVv2 router SHOULD maintain OwnSeqNum in persistent storage. If
an AODVv2 router's OwnSeqNum is lost, it MUST take the following
actions to avoid the danger of routing loops. First, the AODVv2
router MUST invalidate all route table entries, by setting
Route.Broken for each entry. Furthermore the AODVv2 router MUST wait
for at least MAX_SEQNUM_LIFETIME before transmitting or
retransmitting any AODVv2 RREQ or RREP messages. If an AODVv2
protocol message is received during this waiting period, the AODVv2
router SHOULD perform normal route table entry updates. If a data
packet is received for forwarding to another destination during this
waiting period, the AODVv2 router MUST transmit a RERR message
indicating that no route is available. At the end of the waiting
period the AODVv2 router sets its OwnSeqNum to one (1) and begins
performing AODVv2 protocol functions again.
5.6. Enabling Alternate Metrics
Route selection in AODVv2 MANETs depends upon associating metric
information with each route table entry. When presented with
candidate route update information, deciding whether to use the
update involves evaluating the metric. Some applications may require
the consideration of metric information other than Hop Count, which
has traditionally been the default metric associated with routes in
MANET. In fact, it is well known that reliance on Hop Count can
cause selection of the worst possible route in many situations.
It is beyond the scope of this document to describe how applications
specify route selection at the time they launch processing. One
possibility would be to provide a route metric preference as part of
the library routines for opening sockets. In view of the above
considerations, it is important to enable route selection based on
metric information other than Hop Count -- in other words, based on
"alternate metrics". Each such alternate metric identifies a "cost"
of using the associated route, and there are many different kinds of
cost (latency, delay, financial, energy, etc.).
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The most significant change when enabling use of alternate metrics is
to require the possibility of multiple routes to the same
destination, where the "cost" of each of the multiple routes is
measured by a different alternate metric. The other change relevant
to AODVv2 is that the method by which route updates are tested for
usefulness has to be slightly generalized to depend upon a more
abstract method of evaluation which, in this document, is named
"Cost(R)", where 'R' is the route information to be evaluated. From
the above, the route table information for 'R' must always include
the type of metric by which Cost(R) is evaluated, so the metric type
does not have to be shown as a distinct parameter for Cost(R). Since
determining loop freedom is known to depend on comparing the Cost(R)
of route update information to the Cost(R) of an existing stored
route using the same metric, AODVv2 must also be able to invoke an
abstract routine which in this document is called "LoopFree(R1, R2)".
LoopFree(R1, R2) returns TRUE when, given that R2 is loop-free and
Cost(R2) is the cost of route R2, Cost(R1) is known to guarantee loop
freedom of the route R1. In this document, LoopFree(R1,R2) will only
be invoked for routes R1 and R2 which use the same metric.
Generally, HopCount may still be considered the default metric for
use in MANETs, notwithstanding the above objections. Each metric has
to have a Metric Type, and the Metric Type is allocated by IANA as
specified in [RFC6551]. Each Route has to include the Metric Type as
part of the route table entry for that route. Hop Count has Metric
Type assignment 3. The Cost of a route using Metric Type 3 is
naturally the Hop Count between the router and the destination. For
routes R1 and R2 using Metric Type 3, LoopFree (R1, R2) is TRUE when
Cost(R2) <= (Cost(R1) + 1). The specification of Cost(R) and
LoopFree(R1,R2) for metric types other than 3 is beyond the scope of
this document.
Whenever an AODV router receives metric information in an incoming
message, the value of the metric is as measured by the transmitting
router, and does not reflect the cost of traversing the incoming
link. In order to simplify the description of storing accrued route
costs in the route table, the Cost() function is also defined to
return the value of traversing a link 'L'. In other words, the
domain of the Cost() function is enlarged to include links as well as
routes. For Metric Type 3, (i.e., the HopCount metric) Cost(L) = 1
for all links. The specification of Cost(L) for metric types other
than 3 is beyond the scope of this document. Whether the argument of
the Cost() function is a link or a route will, in this document,
always be clear. As a natural result of the way routes are looked up
according to conformant metric type, all intermediate routers
handling a RteMsg will assign the same metric type to all metric
information in the RteMsg.
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For some metrics, a maximum value is defined, namely MAX_METRIC[i]
where 'i' is the Metric Type. AODVv2 does not store routes that cost
more than MAX_METRIC[i]. MAX_METRIC[3] is defined to be
MAX_HOPCOUNT, where as before 3 is the Metric Type of the HopCount
metric.
6. AODVv2 Operations on Route Table Entries
In this section, operations are specified for updating the route
table due to timeouts and route updates within AODVv2 messages. The
route update information in AODVv2 messages includes the destination
IP address (DestIP), SeqNum and prefix length associated with DestIP,
and the Metric from DestIP to the node transmitting the AODVv2
message. DestIP information and prefix length are encoded within an
RFC 5444 Address Block, and the SeqNum and Metric associated with
each DestIP are encoded in RFC 5444 AddrTLVs. Optionally, there may
be AddedNode route updates included in AODVv2 messages, as specified
in Section 13.7. In this section, RteMsg is either RREQ or RREP,
RteMsg.Addr denotes the [i]th address in an RFC 5444 AddrBlk of the
RteMsg, RteMsg.PfxLen denotes the associated prefix length for
RteMsg.Addr, and RteMsg.{field} denotes the corresponding value in
the named AddrTLV block associated with RteMsg.Addr. All SeqNum
comparisons use signed 16-bit arithmetic.
6.1. Evaluating Incoming Routing Information
If the incoming RteMsg does not have a MetricTypeTLV, then the metric
information contained by RteMsg is considered to be of type
DEFAULT_METRIC_TYPE. Whenever an AODVv2 router (HandRtr) handles an
incoming RteMsg (i.e., RREQ or RREP), for every relevant address
(RteMsg.Addr) in the RteMsg, HandRtr searches its route table to see
if there is a route table entry with the same MetricType of the
RteMsg, matching RteMsg.Addr. If not, HandRtr creates a route table
entry for RteMsg.Addr as described in Section 6.2. Otherwise,
HandRtr compares the incoming routing information in RteMsg against
the already stored routing information in the route table entry
(Route) for RteMsg.Addr, as described below.
Suppose a route table entry (Route[RteMsg.Addr]) uses the same metric
type as the incoming routing information, and contains Route.SeqNum,
Route.Metric, and Route.Broken. Suppose the incoming routing
information for Route.Addr is RteMsg.SeqNum and RteMsg.Metric. The
incoming routing information is compared as follows:
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1. Stale:: RteMsg.SeqNum < Route.SeqNum :
If RteMsg.SeqNum < Route.SeqNum the incoming information is stale.
Using stale routing information is not allowed, since that might
result in routing loops. HandRtr MUST disregard the routing
information for RteMsg.Addr.
2. Unsafe against loops:: (TRUE != LoopFree (RteMsg, Route)) :
If RteMsg is not Stale (as in (1)), RteMsg.Metric is next
considered to insure loop freedom. If (TRUE != LoopFree (RteMsg,
Route)) (see Section 5.6), then the incoming RteMsg information is
not guaranteed to prevent routing loops, and it MUST NOT be used.
3. Longer::
(RteMsg.Metric >= Route.Metric) && (Route.Broken==FALSE)
When RteMsg.SeqNum is the same as in a valid route table entry,
and LoopFree (RteMsg, Route) assures loop freedom, incoming
information still does not offer any improvement over the existing
route table information if RteMsg.Metric >= Route.Metric. Using
such incoming routing information to update a route table entry is
not recommended.
4. Offers improvement::
Incoming routing information that does not match any of the above
criteria is better than existing routing table information and
SHOULD be used to improve the route table. The following pseudo-
code illustrates whether incoming routing information should be
used to update an existing route table entry as described in
Section 6.2.
(RteMsg.SeqNum > Route.SeqNum) OR
{(RteMsg.SeqNum == Route.SeqNum) AND
[(RteMsg.Metric < Route.Metric) OR
((Route.Broken == TRUE) && LoopFree (RteMsg, Route))]}
The above logic corresponds to placing the following conditions on
the incoming route update (compared to the existing route table
entry) before it can be used:
* it is more recent, or
* it is not stale and is shorter, or
* it can safely repair a broken route.
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6.2. Applying Route Updates To Route Table Entries
To apply the route update, the route table entry is populated with
the following information:
o Route.Address := RteMsg.Addr
o If (RteMsg.PfxLen != 0), then Route.PfxLen := RteMsg.PfxLen
o Route.SeqNum := RteMsg.SeqNum
o Route.NextHopAddress := IP.SourceAddress (i.e., an address of the
node from which the RteMsg was received)
o Route.NextHopInterface is set to the interface on which RteMsg was
received
o Route.Broken flag := FALSE
o If RteMsg.MetricType is included, then
Route.MetricType := RteMsg.MetricType. Otherwise,
Route.MetricType := DEFAULT_METRIC_TYPE.
o Route.MetricType := RteMsg.MetricType
o Route.Metric := RteMsg.Metric
o Route.LastUsed := Current_Time
o If RteMsg.VALIDITY_TIME is not included, then
Route.ExpirationTime := MAXTIME, otherwise Route.ExpirationTime :=
Current_Time + RteMsg.VALIDITY_TIME
With these assignments to the route table entry, a route has been
made available, and the route can be used to send any buffered data
packets and subsequently to forward any incoming data packets for
Route.Addr. An updated route entry also fulfills any outstanding
route discovery (RREQ) attempts for Route.Addr.
6.3. Route Table Entry Timeouts
During normal operation, AODVv2 does not require any explicit
timeouts to manage the lifetime of a route. However, the route table
entry MUST be examined be before using it to forward a packet, as
discussed in Section 8.1. Any required expiry or deletion can occur
at that time. Nevertheless, it is permissible to implement timers
and timeouts to achieve the same effect.
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At any time, the route table can be examined and route table entries
can be expunged according to their current state at the time of
examination, as follows.
o An Active route MUST NOT be expunged.
o An Idle route SHOULD NOT be expunged.
o An Expired route MAY be expunged (least recently used first).
o A route MUST be expunged if (Current_Time - Route.LastUsed) >=
MAX_SEQNUM_LIFETIME.
o A route MUST be expunged if Current_Time >= Route.ExpirationTime
If precursor lists are maintained for the route (as described in
Section 13.3) then the precursor lists must also be expunged at the
same time that the route itself is expunged.
7. Routing Messages RREQ and RREP (RteMsgs)
AODVv2 message types RREQ and RREP are together known as Routing
Messages (RteMsgs) and are used to discover a route between an
Originating and Target Node, denoted here by OrigNode and TargNode.
The constructed route is bidirectional, enabling packets to flow
between OrigNode and TargNode. RREQ and RREP have similar
information and function, but have some differences in their rules
for handling. The main difference between the two messages is that
RREQ messages are typically multicast to solicit a RREP, whereas RREP
is typically unicast as a response to RREQ.
When an AODVv2 router needs to forward a data packet from a node
(OrigNode) in its set of router clients, and it does not have a
forwarding route toward the packet's IP destination address
(TargNode), the AODVv2 router (in this section, called RREQ_Gen)
generates a RREQ (as described in Section 7.3) to discover a route
toward TargNode. Subsequently RREQ_Gen awaits reception of an RREP
message (see Section 7.4) or other route table update (see
Section 6.2) to establish a route toward TargNode. The RREQ message
contains routing information to enable RREQ recipients to route
packets back to OrigNode, and the RREP message contains routing
information enabling RREP recipients to route packets to TargNode.
7.1. Route Discovery Retries and Buffering
After issuing a RREQ, as described above RREQ_Gen awaits a RREP
providing a bidirectional route toward Target Node. If the RREP is
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not received within RREQ_WAIT_TIME, RREQ_Gen may retry the Route
Discovery by generating another RREQ. Route Discovery SHOULD be
considered to have failed after DISCOVERY_ATTEMPTS_MAX and the
corresponding wait time for a RREP response to the final RREQ. After
the attempted Route Discovery has failed, RREQ_Gen MUST wait at least
RREQ_HOLDDOWN_TIME before attempting another Route Discovery to the
same destination.
To reduce congestion in a network, repeated attempts at route
discovery for a particular Target Node SHOULD utilize an binary
exponential backoff.
Data packets awaiting a route SHOULD be buffered by RREQ_Gen. This
buffer SHOULD have a fixed limited size (BUFFER_SIZE_PACKETS or
BUFFER_SIZE_BYTES). Determining which packets to discard first is a
matter of policy at each AODVv2 router; in the absence of policy
constraints, by default older data packets SHOULD be discarded first.
Buffering of data packets can have both positive and negative effects
(albeit usually positive). Nodes without sufficient memory available
for buffering SHOULD be configured to disable buffering by
configuring BUFFER_SIZE_PACKETS == 0 and BUFFER_SIZE_BYTES == 0.
Doing so will affect the latency required for launching TCP
applications to new destinations.
If a route discovery attempt has failed (i.e., DISCOVERY_ATTEMPTS_MAX
attempts have been made without receiving a RREP) to find a route
toward the Target Node, any data packets buffered for the
corresponding Target Node MUST BE dropped and a Destination
Unreachable ICMP message (Type 3) SHOULD be delivered to the source
of the data packet. The code for the ICMP message is 1 (Host
unreachable error). If RREQ_Gen is not the source (OrigNode), then
the ICMP is sent over the interface from which OrigNode sent the
packet to the AODVv2 router.
7.2. RteMsg Structure
RteMsgs have the following general format:
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+---------------------------------------------------------------+
| RFC 5444 Packet Header |
+---------------------------------------------------------------+
| RFC 5444 Message Header <msg-hopcount> |
+---------------------------------------------------------------+
| RFC 5444 MsgHdr, opt. DestOnly TLV, opt. MetricTypeTLV |
+---------------------------------------------------------------+
| RteAddrBlk {[1]:=RREQ.OrigNode,[2]:=RREQ.TargNode)} |
+---------------------------------------------------------------+
| RteSeqNumTLV (OrigRtr.Seqnum, TargNode.Seqnum) |
+---------------------------------------------------------------+
| Added Node Address Block (Optional) |
+---------------------------------------------------------------+
| Added Node Address TLV (SeqNum) |
+---------------------------------------------------------------+
| Added Node Address TLV (Metric[MetricType]) |
+---------------------------------------------------------------+
Figure 1: RREQ and RREP (RteMsg) message structure
Message Header
This is typically mostly boilerplate but can contain MsgTLVs as
below.
DestOnly TLV
RREQ only: no Intermediate RREP.
MetricType TLV
Metric Type for Metric AddrTLV
RteAddrBlk
This Address Block contains the IP addresses for RREQ Originating
and Target Node (OrigNode and TargNode). Note that for both RREP
and RREQ, the OrigNode and TargNode are as identified in the
context of the RREQ message originator.
RteSeqNumTLV (Sequence Number AddrTLV)
This Address Block TLV is REQUIRED and carries the destination
sequence numbers associated with either OrigNode or TargNode or
both.
(Optional) Added Node AddrBlk
AODVv2 allows the inclusion of routing information for other nodes
in addition to OrigNode and TargNode.
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(Optional) SeqNum AddrTLV If the Added Node AddrBlk is present, the
SeqNum AddrTLV is REQUIRED, to carry the destination sequence
numbers associated with the Added Nodes.
(Optional) Metric AddrTLV If the Added Node AddrBlk is present, this
AddrTLV is REQUIRED, to carry the metric information associated
with the Added Nodes. See Below.
The metric AddrTLV may be either a Metric8 AddrTLV or an Metric16
AddrTLV.
7.3. RREQ Generation
RREQ_Gen generates the RREQ according to the following steps, with
order of protocol elements illustrated schematically in Figure 1.
1. RREQ_Gen MUST increment its OwnSeqNum by one (1) according to the
rules specified in Section 5.5. This assures that all nodes with
existing routing information will use RREQ_Gen's new information
to update existing routing table information.
2. OrigNode MUST be a unicast address. If RREQ_Gen is not OrigNode,
then OwnSeqNum will be used as the value of OrigNode.SeqNum. will
be used by AODVv2 routers to create a route toward the OrigNode,
enabling a RREP from TargRtr, and eventually used for proper
forwarding of data packets.
3. If RREQ_Gen requires that only TargRtr is allowed to generate a
RREP, then RREQ_Gen includes the "Destination RREP Only" TLV as
part of the RFC 5444 message header. This also assures that
TargRtr increments its sequence number. Otherwise, intermediate
AODVv2 routers MAY respond to the RREQ_Gen's RREQ if they have an
valid route to TargNode (see Section 13.2).
4. msg-hopcount MUST be set to 0.
* This RFC 5444 constraint causes the typical RteMsg payload
incur additional enlargement.
5. RREQ_Gen adds the TargNode.Addr to the RREQ.
6. If a previous value of the TargNode's SeqNum is known (e.g., from
an invalid routing table entry using longest-prefix matching),
RREQ_Gen SHOULD include TargNode.SeqNum in all but the last RREQ
attempt. If TargNode.SeqNum is not included, it is assumed to be
unknown by AODVv2 routers handling the RREQ; if the optional
feature Intermediate RREP is enabled, then any route to TargNode
will satisfy the RREQ [I-D.perkins-irrep].
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7. RREQ_Gen adds OrigNode.Addr, its prefix, and the RREQ_Gen.SeqNum
(OwnSeqNum) to the RREQ.
8. If OrigNode.Metric is included it is set to the cost of the route
between OrigNode and RREQ_Gen.
An example RREQ message format is illustrated in Appendix A.1.
7.4. RREP Generation
An AODVv2 router (TargRtr, called in this section RREP_Gen) generates
a RREP in order to provide a route to the Target Node (TargNode) of a
RREQ, thus satisfying the routing requirement for packets to flow
between OrigNode and TargNode. This section specifies the generation
of an RREP by the RREP_Gen. The basic format of an RREP conforms to
the structure for RteMsgs as illustrated in Figure 1. Optionally,
RREP messages may be generated by AODVv2 routers other than TargRtr;
this optional message generation is known as "Intermediate RREP"
generation, and is specified in Internet Draft [I-D.perkins-irrep].
If TargNode is not a unicast IP address the RREP MUST NOT be
generated, and processing for the RREQ is complete.
Otherwise RREP_Gen generates the RREP as follows:
1. RREP_Gen first uses the routing information to update its route
table entry for OrigNode if necessary as specified in
Section 6.2.
2. RREP_Gen MUST increment its OwnSeqNum by one (1) according to
the rules specified in Section 5.5.
3. RREP.AddrBlk[OrigNode] := RREQ.AddrBlk[OrigNode]
4. RREP.AddrBlk[TargNode] := RREQ.AddrBlk[TargNode]
5. RREP.SeqNumTLV[OrigNode] := RREQ.SeqNumTLV[OrigNode]
6. RREP.SeqNumTLV[TargNode] := OwnSeqNum
7. If Route[TargNode].PfxLen/8 is equal to the number of bytes in
the addresses of the RREQ (4 for IPv4, 16 for IPv6), then no
<prefix-length> is included with the iRREP. Otherwise,
RREP.PfxLen[TargNode] := RREQ.PfxLen[TargNode] according to the
rules of RFC 5444 AddrBlk encoding.
8. RREP.MetricType[TargNode] := Route[TargNode].MetricType
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9. RREP.Metric[TargNode] := Route[TargNode].Metric
10. <msg-hop-limit> SHOULD be set to RteMsg.<msg-hop-count>.
11. IP.DestinationAddr := Route[OrigNode].NextHop
The message format for RREP is illustrated in Appendix A.2.
7.5. Handling a Received RteMsg
Before an AODVv2 router (HandlingRtr) can process a received RteMsg
(i.e., RREQ or RREP), it first must verify that the RteMsg is
permissible according to the following steps. For RREQ, RteMsg_Gen
is OrigRtr, also called RREQ_Gen. For RREP, RteMsg_Gen is TargRtr,
also called RREP_Gen.
1. HandlingRtr MUST handle AODVv2 messages only from adjacent
routers as specified in Section 5.4. AODVv2 messages from other
sources MUST be disregarded.
2. If the RteMsg.<msg-hop-limit> is equal to 0, then the message is
disregarded.
3. If the RteMsg.<msg-hop-count> is present, and RteMsg.<msg-hop-
count> >= MAX_HOPCOUNT, then the message is disregarded.
4. HandlingRtr examines the RteMsg to ascertain that it contains the
required information: TargNode.Addr, OrigNode.Addr,
RteMsg_Gen.Metric and RteMsg_Gen.SeqNum. If the required
information does not exist, the message is disregarded.
5. HandlingRtr checks that OrigNode.Addr and TargNode.Addr are valid
routable unicast addresses. If not, the message is disregarded.
6. HandlingRtr checks that the Metric Type associated with
OrigNode.Metric and TargNode.Metric is known, and that Cost(L)
can be computed. If not, the message is disregarded.
* DISCUSSION: alternatively, can change the AddrBlk metric to
use HopCount, measured from<msg-hop-limit>.
7. If MAX_METRIC[RteMsg.MetricType] <= (RteMsg_Gen.Metric +
Cost(L)), where 'L' is the incoming link, the RteMsg is
disregarded.
An AODVv2 router (HandlingRtr) handles a permissible RteMsg according
to the following steps.
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1. HandlingRtr MUST process the routing information contained in the
RteMsg as speciied in Section 6.1.
2. HandlingRtr MAY process AddedNode routing information (if
present) as specified in Section 13.7.1 Otherwise, if AddedNode
information is not processed, it MUST be deleted.
3. By sending the updated RteMsg, HandlingRtr advertises that it
will route for addresses contained in the outgoing RteMsg based
on the information enclosed. HandlingRtr MAY choose not to send
the RteMsg, though not resending this RteMsg could decrease
connectivity in the network or result in a nonoptimal path. The
circumstances under which HandlingRtr might choose to not re-
transmit a RteMsg are not specified in this document. Some
examples might include the following:
* HandlingRtr is already heavily loaded and does not want to
advertise routing for the contained addresses
* HandlingRtr recently transmitted identical routing information
(e.g. in a RteMsg advertising the same metric)
* HandlingRtr is low on energy and has to reduce energy expended
for sending protocol messages or packet forwarding
Unless HandlingRtr is prepared to send an updated RteMsg, it
halts processing. Otherwise, processing continues as follows.
4. HandlingRtr MUST decrement RteMsg.<msg-hop-limit>. If
RteMsg.<msg-hop-limit> is then zero (0), no further action is
taken.
5. HandlingRtr MUST increment RteMsg.<msg-hop-count>.
Further actions to send an updated RteMsg depend upon whether the
RteMsg is an RREP or an RREQ
7.5.1. Additional Handling for Outgoing RREQ
o If the upstream router is in the Blacklist, and Current_Time <
BlacklistRmTime, then HandlingRtr MUST NOT transmit any outgoing
RREQ, and processing is complete.
o Otherwise, if the upstream router is in the Blacklist, and
Current_Time >= BlacklistRmTime, then the upstream router SHOULD
be removed from the Blacklist, and message processing continued.
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o If TargNode is a client of HandlingRtr, then a RREP is generated
by the HandlingRtr (i.e., TargRtr) and unicast to the upstream
router towards the RREQ OrigNode, as specified in Section 7.4.
Afterwards, TargRtr processing for the RREQ is complete.
o If HandlingRtr is not the TargetNode, then the outgoing RREQ (as
altered by the procedure defined above) SHOULD be sent to the IP
multicast address LL-MANET-Routers [RFC5498]. If the RREQ is
unicast, the IP.DestinationAddress is set to the NextHopAddress.
7.5.2. Additional Handling for Outgoing RREP
o If HandlingRtr is not OrigRtr then the outgoing RREP is sent to
the Route.NextHopAddress for the RREP.AddrBlk[OrigNode]. If no
forwarding route exists to OrigNode, then a RERR SHOULD be
transmitted to RREP.AddrBlk[TargNode]. See Table 1 for notational
conventions; OrigRtr, OrigNode, and TargNode are routers named in
the context of OrigRtr, that is, the router originating the RREQ
to which the RREP is responding.
8. Route Maintenance
AODVv2 routers attempt to maintain active routes. When a routing
problem is encountered, an AODVv2 router (namely, RERR_Gen) attempts
to quickly notify upstream routers. Two kinds of routing problems
may trigger generation of a RERR message. The first case happens
when the router receives a packet but does not have a route for the
destination of the packet. The second case happens immediately upon
detection of a broken link (see Section 8.2) of an Active route, to
quickly notify AODVv2 routers that that route is no longer available.
When the RERR message is generated, it MUST be the only message in
the RFC 5444 packet.
8.1. Handling Route Lifetimes During Packet Forwarding
Before using a route to forward a packet, an AODVv2 router MUST check
the status of the route as follows.
If the route is marked has been marked as Broken, it cannot be
used for forwarding.
If Current_Time > Route.ExpirationTime, the route table entry has
expired, and a RERR SHOULD be generated.
Similarly, if (Route.ExpirationTime == MAXTIME), and if
Current_Time - Route.LastUsed > (ACTIVE_INTERVAL+MAX_IDLETIME),
the route has expired, and a RERR SHOULD be generated.
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Furthermore, if Current_Time - Route.LastUsed >
(MAX_SEQNUM_LIFETIME), the route table entry MUST be expunged.
Otherwise, if none of the above route error conditions are indicated,
Route.LastUsed := Current_Time, and the packet is forwarded to the
route's next hop.
Optionally, if a precursor list is maintained for the route, see
Section 13.3 for precursor lifetime operations.
8.2. Active Next-hop Router Adjacency Monitoring
Nodes SHOULD monitor connectivity to adjacent next-hop AODVv2 routers
on forwarding routes. This monitoring can be accomplished by one or
several mechanisms, including:
o Neighborhood discovery [RFC6130]
o Route timeout
o Lower layer trigger that a neighboring router is no longer
reachable
o Other monitoring mechanisms or heuristics
Upon determining that a next-hop AODVv2 router has become
unreachable, RERR_Gen follows the procedures specified in
Section 8.3.2.
8.3. RERR Generation
An RERR message is generated by a AODVv2 router (in this section,
called RERR_Gen) in order to to notify upstream routers that packets
cannot be delivered to certain destinations. An RERR message has the
following general structure:
+---------------------------------------------------------------+
| RFC 5444 Packet Header |
+---------------------------------------------------------------+
| RFC 5444 Message Header <msg-hoplimit> <msg-hopcount> |
+---------------------------------------------------------------+
| UnreachableNode AddrBlk (Unreachable Node addresses) |
+---------------------------------------------------------------+
| UnreachableNode SeqNum AddrBlk TLV |
+---------------------------------------------------------------+
Figure 2: RERR message structure
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Message Header
RFC 5444 MsgHdr may contain the following options:
* <msg-hop-limit>
* <msg-hop-count>
* PktSource MsgTLV
UnreachableNode AddrBlk
This Address Block contains the IP addresses unreachable by AODVv2
router transmitting the RERR.
Sequence Number AddrBlk TLV
This Address Block TLV carries the destination sequence number
associated with the UnreachableNodes when that information is
available.
UnreachableNode.PfxLen
The prefix length associated with an UnreachableNode.
There are two kinds of events indicating that packets cannot be
delivered to certain destinations. The two cases differ in the way
that the neighboring IP destination address for the RERR (i.e.,
RERR_dest) is chosen, and in the way that the set of UnreachableNodes
is identified.
In both cases, the MsgHdr.<msg-hop-limit> MUST be set to
MAX_HOPCOUNT. MsgHdr.<msg-hop-count> SHOULD be be included and set
to 0, to facilitate use of various route repair strategies including
Intermediate RREP [I-D.perkins-irrep].
8.3.1. Case 1: Undeliverable Packet
The first case happens when the router receives a packet but does not
have a valid route for the destination of the packet. In this case,
there is exactly one UnreachableNode to be included in the RERR's
AddrBlk. RERR_dest SHOULD be the multicast address LL-MANET-Routers,
but RERR_Gen MAY instead set RERR_dest to be the next hop towards the
source IP address of the packet which was undeliverable. In the
latter case, the PktSource MsgTLV MUST be included, containing the
the source IP address of the undeliverable packet. If a value for
the UnreachableNode's SeqNum (UnreachableNode.SeqNum) is known, it
MUST be placed in the RERR. Otherwise, if no Seqnum AddrTLV is
included, all nodes handling the RERR will assume their route through
RERR_Gen towards the UnreachableNode is no longer valid and flag
those routes as broken. RERR_Gen MUST discard the packet or message
that triggered generation of the RERR.
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8.3.2. Case 2: Broken Link
The second case happens when the link breaks to an active downstream
neighbor (i.e., the next hop of an active route). In this case,
RERR_dest MUST be the multicast address LL-MANET-Routers, except when
the optional feature of maintaining precursor lists is used as
specified in Section 13.3. All Active, Idle and Expired routes that
use the broken link MUST be marked as Broken. The set of
UnreachableNodes is initialized by identifying those Active routes
which use the broken link. For each such Active Route, Route.Dest is
added to the set of Unreachable Nodes. After the Active Routes using
the broken link have all been included as UnreachableNodes, idle
routes MAY also be included, as long as the packet size of the RERR
does not exceed the MTU of the physical medium.
If the set of UnreachableNodes is empty, no RERR is generated.
Otherwise, RERR_Gen generates a new RERR, and the address of each
UnreachableNode (IP.DestinationAddress from a data packet or
RREP.TargNode.Address) is inserted into an AddrBlock. If a prefix is
known for the UnreachableNode.Address, it SHOULD be included.
Otherwise, the UnreachableNode.Address is assumed to be a host
address with a full length prefix. The value for each
UnreachableNode's SeqNum (UnreachableNode.SeqNum) MUST be placed in a
SeqNum AddrTLV. If none of UnreachableNode.Addr entries are
associated with known prefix lengths, then the AddrBLK SHOULD NOT
include any prefix-length information. Otherwise, for each
UnreachableNode.Addr that does not have any associated prefix-length
information, the prefix-length for that address MUST be assigned to
zero.
8.4. Receiving and Handling RERR Messages
When an AODVv2 router (HandlingRtr) receives a RERR message, it uses
the information provided to invalidate affected routes. If the
information in the RERR may be useful to upstream neighbors using
those routes, HandlingRtr subsequently sends another RERR to those
neighbors. This operation has the effect of retransmitting the RERR
information and is counted as another "hop" for purposes of properly
modifying Msg.<msg-hop-limit> and Msg.<msg-hop-count>.
HandlingRtr examines the incoming RERR to assure that it contains
Msg.<msg-hop-limit> and at least one UnreachableNode.Address. If the
required information does not exist, the incoming RERR message is
disregarded and further processing stopped. Otherwise, for each
UnreachableNode.Address, HandlingRtr searches its route table for a
route using longest prefix matching. If no such Route is found,
processing is complete for that UnreachableNode.Address. Otherwise,
HandlingRtr verifies the following:
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1. The UnreachableNode.Address is a routable unicast address.
2. Route.NextHopAddress is the same as RERR IP.SourceAddress.
3. Route.NextHopInterface is the same as the interface on which the
RERR was received.
4. The UnreachableNode.SeqNum is unknown, OR Route.SeqNum <=
UnreachableNode.SeqNum (using signed 16-bit arithmetic).
If the route satisfies all of the above conditions, HandlingRtr sets
the Route.Broken flag for that route. Furthermore, if Msg.<msg-hop-
limit> is greater than 0, then HandlingRtr adds the UnreachableNode
address and TLV information to an AddrBlk for for delivery in the
outgoing RERR message to one or more of HandlingRtr's upstream
neighbors.
If there are no UnreachableNode addresses to be transmitted in an
RERR to upstream routers, HandlingRtr MUST discard the RERR, and no
further action is taken.
Otherwise, Msg.<msg-hop-limit> is decremented by one (1) and
processing continues as follows:
o If precursor lists are (optionally) maintained, the outgoing RERR
SHOULD be sent to the active precursors of the broken route as
specified in Section 13.3.
o Otherwise, if the incoming RERR message was received at the LL-
MANET-Routers [RFC5498] multicast address, the outgoing RERR
SHOULD also be sent to LL-MANET-Routers.
o Otherwise, if the PktSource MsgTLV is present, and HandlingRtr has
a Route to PktSource.Addr, then HandlingRtr MUST send the outgoing
RERR to Route[PktSource.Addr].NextHop.
o Otherwise, the outgoing RERR MUST be sent to LL-MANET-Routers.
9. Unknown Message and TLV Types
If a message with an unknown type is received, the message is
disregarded.
For handling of messages that contain unknown TLV types, ignore the
information for processing, preserve it unmodified for forwarding.
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10. Simple Internet Attachment
Simple Internet attachment means attachment of a stub (i.e., non-
transit) network of AODVv2 routers to the Internet via a single
Internet AODVv2 router (called IAR).
As in any Internet-attached network, AODVv2 routers, and their
clients, wishing to be reachable from hosts on the Internet MUST have
IP addresses within the IAR's routable and topologically correct
prefix (e.g. 191.0.2.0/24).
The IAR is responsible for generating RREQ messages to find nodes
within the MANET on behalf of nodes on the Internet, as well as
responding to route requests from the AODVv2 MANET on behalf of the
nodes on the Internet.
/-------------------------\
/ +----------------+ \
/ | AODVv2 Router | \
| | 191.0.2.2/32 | |
| +----------------+ | Routable
| +-----+--------+ Prefix
| | Internet | /191.0.2/24
| | AODVv2 Router| /
| | 191.0.2.1 |/ /----------------\
| | serving net +-------+ Internet \
| | 191.0.2/24 | \ /
| +-----+--------+ \----------------/
| +----------------+ |
| | AODVv2 Router | |
| | 191.0.2.3/32 | |
\ +----------------+ /
\ /
\-------------------------/
Figure 3: Simple Internet Attachment Example
When an AODVv2 router within the AODVv2 MANET wants to discover a
route toward a node on the Internet, it uses the normal AODVv2 route
discovery for that IP Destination Address. The IAR MUST respond to
RREQ on behalf of all Internet destinations.
When a packet from a node on the Internet destined for a node in the
AODVv2 MANET reaches the IAR, if the IAR does not have a route toward
that destination it will perform normal AODVv2 route discovery for
that destination.
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11. Multiple Interfaces
AODVv2 may be used with multiple interfaces; therefore, the
particular interface over which packets arrive MUST be known whenever
a packet is received. Whenever a new route is created, the interface
through which the Route.Address can be reached is also recorded in
the route table entry.
When multiple interfaces are available, a node transmitting a
multicast packet with IP.DestinationAddress set to LL-MANET-Routers
SHOULD send the packet on all interfaces that have been configured
for AODVv2 operation.
Similarly, AODVv2 routers SHOULD subscribe to LL-MANET-Routers on all
their AODVv2 interfaces.
12. AODVv2 Control Packet/Message Generation Limits
To avoid messaging overload, each AODVv2 router's rate of packet/
message generation SHOULD be limited. The rate and algorithm for
limiting messages (CONTROL_TRAFFIC_LIMITS) is left to the implementor
and should be administratively configurable. AODVv2 messages SHOULD
be discarded in the following order of preference: RREQ, RREP, and
finally RERR.
13. Optional Features
Some optional features of AODVv2, associated with AODV, are not
required by minimal implementations. These features are expected to
be useful in networks with greater mobility, or larger node
populations, or requiring shorter latency for application launches.
The optional features are as follows:
o Expanding Rings Multicast
o Intermediate RREPs (iRREPs): Without iRREP, only the destination
can respond to a RREQ.
o Precursor lists.
o Reporting Multiple Unreachable Nodes. An RERR message can carry
more than one Unreachable Destination node for cases when a single
link breakage causes multiple destinations to become unreachable
from an intermediate router.
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o RREP_ACK.
o Message Aggregation.
o Inclusion of Added Routing Information.
13.1. Expanding Rings Multicast
For multicast RREQ, Msg.<msg-hop-limit> MAY be set in accordance with
an expanding ring search as described in [RFC3561] to limit the RREQ
propagation to a subset of the local network and possibly reduce
route discovery overhead.
13.2. Intermediate RREP
This specification has been published as a separate Internet Draft
[I-D.perkins-irrep].
13.3. Precursor Lists and Notifications
This section specifies an interoperable enhancement to AODVv2 (and
possibly other reactive routing protocols) enabling more economical
notifications to active sources of traffic upon determination that a
route needed to forward such traffic to its destination has become
Broken.
13.3.1. Overview
In many circumstances, there might be several sources of traffic for
any particular destination. Each such source of traffic is known as
a "precursor" for the destination, as well as all upstream routers
between the forwarding AODVv2 router and the traffic source. For
each active destination, an AODVv2 router MAY choose to keep track of
the upstream neighbors that have provided traffic for that
destination; there is no need to keep track of upstream routers any
farther away than the next hop.
Moreover, any particular link to an adjacent AODVv2 router may be a
path component of multiple routes towards various destinations. The
precursors for all destinations using the next hop across any link
are collectively known as the precursors for that next hop.
When an AODVv2 router determines that an active link to one of its
downstream neighbors has broken, the AODVv2 router detecting the
broken link must mark multiple routes as Broken, for each of the
newly unreachable destinations, as described in Section 8.3. Each
route that relies on the newly broken link is no longer valid.
Furthermore, the precursors of the broken link should be notified
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(using RERR) about the change in status of their route to a
destination downstream along the broken next hop.
13.3.2. Precursor Notification Details
During normal operation, each AODVv2 router wishing to maintain
precursor lists as described above, maintains a precursor table and
updates the table whenever the node forwards traffic to one of the
destinations in its route table. For each precursor in the precursor
list, a record must be maintained to indicate whether the precursor
has been used for recent traffic (in other words, whether the
precursor is an Active precursor). So, when traffic arrives from a
precursor, the Current_Time is used to mark the time of last use for
the precursor list element associated with that precursor.
When an AODVv2 router detects that a link is broken, then for each
precursor using that next hop, the node MAY notify the precursor
using either unicast or multicast RERR:
unicast RERR to each Active precursor
This option is useful when there are few Active precursors
compared to the number of neighboring AODVv2 routers.
multicast RERR to RERR_PRECURSORS
RERR_PRECURSORS is, by default, LL-MANET-Routers [RFC5498]. This
option is typically preferable since fewer packet transmissions
are required.
Each active upstream neighbor (i.e., precursor) MAY then execute the
same procedure until all active upstream routers have received the
RERR notification.
13.4. Multicast RREP Response to RREQ
The RREQ Target Router (RREP_Gen) MAY, as an alternative to
unicasting a RREP, be configured to distribute routing information
about the route toward the RREQ TargNode (TargRtr's client) more
widely. That is, RREP_Gen MAY be configured respond to a route
discovery by generating a RREP, using the procedure in Section 7.4,
but multicasting the RREP to LL-MANET-Routers [RFC5498]. Afterwards,
RREP_Gen processing for the incoming RREQ is complete.
Broadcast response to incoming RREQ was originally specified to
handle unidirectional links, but it is expensive. Due to the
significant overhead, AODVv2 routers MUST NOT use multicast RREP
unless configured to do so by setting the administrative parameter
USE_MULTICAST_RREP.
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13.5. RREP_ACK
Instead of relying on existing mechanisms for requesting verification
of link bidirectionality during Route Discovery, RREP_Ack is provided
as an optional feature and modeled on the RREP_Ack message type from
AODV [RFC3561].
Since the RREP_ACK is simply echoed back to the node from which the
RREP was received, there is no need for any additional RFC 5444
address information (or TLVs). Considerations of packet TTL are as
specified in Section 5.4. The message format is illustrated in
section Appendix A.4.
13.6. Message Aggregation
The aggregation of multiple messages into a packet is specified in
RFC 5444 [RFC5444].
Implementations MAY choose to briefly delay transmission of messages
for the purpose of aggregation (into a single packet) or to improve
performance by using jitter [RFC5148].
13.7. Added Routing Information in RteMsgs
DSR [RFC4728] includes source routes as part of the data of its RREPs
and RREQs. Doign so allows additional topology information to be
multicast along with the RteMsg, and potentially allows updating for
stale routing information at MANET routers along new paths between
source and destination. To maintain this functionality, AODVv2 has
defined a somewhat more general method that enables inclusion of
source routes in RteMsgs.
Appending routing information can eliminate some route discovery
attempts to the nodes whose information is included, if handling
AODVv2 routers use this information to update their routing tables.
Note that, since the initial merger of DSR with AODV to create this
protocol, further experimentation has shown that including the
additional routing information is not always helpful. Sometimes it
seems to help, and other times it seems to reduce overall
performance. The results depend upon packet size and traffic
patterns.
13.7.1. Including Added Node Information
An AODVv2 router (HandlingRtr) MAY optionally append AddedNode
routing information to a RteMsg. This is controllable by an option
(APPEND_INFORMATION) which SHOULD be administratively configurable or
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controlled according to the traffic characteristics of the network.
The following notation is used to specify the methods for inclusion
of routing information for addtional nodes.
AddedNode
The IP address of an additional node that can be reached via the
AODVv2 router adding this information. Each AddedNode.Address
MUST include its prefix. Each AddedNode.Address MUST also have an
associated Node.SeqNum in the address TLV block.
AddedNode.SeqNum
The AODVv2 sequence number associated with this routing
information.
AddedNode.Metric
The cost of the route needed to reach the associated
AddedNode.Address. This field is increased by Cost(L) at each
intermediate AODVv2 router, where 'L' is the incoming link. If,
for the Metric Type of the AddrBlk, it is not known how to compute
Cost(L), the AddedNode.Addr information MUST be deleted from the
AddedNode AddrBlk.
The VALIDITY_TIME of routing information for appended address(es)
MUST be included, to inform routers about when to expire this
information. A typical value for VALIDITY_TIME is (ACTIVE_INTERVAL+
MAX_IDLETIME) - (Current_Time - Route.LastUsed) but other values
(less than MAX_SEQNUM_TIME) MAY be chosen. The VALIDITY_TIME TLV is
defined in [RFC5497].
SeqNum and Metric AddrTLVs about any appended address(es) MUST be
included.
Routing information about the TargNode MUST NOT be added to the
AddedAddrBlk. Also, duplicate address entries SHOULD NOT be added.
Only the best routing information (Section 6.1) for a particular
address SHOULD be included; if route information is included for a
destination address already in the AddedAddrBlk, the previous
information SHOULD NOT be included in the outgoing RteMsg.
13.7.2. Handling Added Node Information
An intermediate node (i.e., HandlingRtr) obeys the following
procedures when processing AddedNode.Address information and other
associated TLVs that are included with a RteMsg. For each AddedNode
(except the TargetNode) in the RteMsg, the AddedNode.Metric
information MUST be increased by Cost(L), where 'L' is the incoming
link. If, for the Metric Type of the AddrBlk, it is not known how to
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compute Cost(L), the AddedNode.Addr information MUST be deleted from
the AddedNode AddrBlk. If the resulting Cost of the route to the
AddedNode is greater than MAX_METRIC[i], the AddedNode information is
discarded. If the resulting Distance value for another node is
greater than MAX_METRIC[i], the associated address and its
information are removed from the RteMsg.
After handling the OrigNode's routing information, then each address
that is not the TargetNode MAY be considered for creating and
updating routes. Creating and updating routes to other nodes can
eliminate RREQ for those IP destinations, in the event that data
needs to be forwarded to the IP destination(s) now or in the near
future.
For each of the additional addresses considered, HandlingRtr first
checks that the address is a routable unicast address. If the
address is not a unicast address, then the address and all related
information MUST be removed.
If the routing table does not have a matching route with a known
Route.SeqNum for this additional address using longest-prefix
matching, then a route MAY be created and updated as described in
Section 6.2. If a route table entry exists with a known
Route.SeqNum, the incoming routing information is compared with the
route table entry following the procedure described in Section 6.1.
If the incoming routing information is used, the route table entry
SHOULD be updated as described in Section 6.2.
If the routing information for an AddedNode.Address is not used, then
it is removed from the RteMsg.
If route information is included for a destination address already in
the AddedAddrBlk, the previous information SHOULD NOT be included in
the outgoing RteMsg.
14. Administratively Configured Parameters and Timer Values
AODVv2 contains several parameters which MUST be administratively
configured. The list of these follows:
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+------------------------+------------------------------------------+
| Name | Description |
+------------------------+------------------------------------------+
| CLIENT_ADDRESSES | List of addresses and routing prefixes, |
| | for which this AODVv2 router is |
| | responsible. If the list is empty, this |
| | AODVv2 router is only responsible for |
| | its own addresses. |
| USE_MULTICAST_RREP | Whether or not to use multicast RREP |
| | (see Section 13.4). |
| DEFAULT_METRIC_TYPE | 3 (Hop Count {see [RFC6551]} |
| AODVv2_INTERFACES | List of the interfaces participating in |
| | AODVv2 routing protocol. |
+------------------------+------------------------------------------+
Table 2: Required Administratively Configured Parameters
AODVv2 requires certain timing information to be associated with
route table entries. The default values are as follows:
+------------------------------+-------------+
| Name | Value |
+------------------------------+-------------+
| ACTIVE_INTERVAL | 5 second |
| MAX_IDLETIME | 200 seconds |
| MAX_SEQNUM_LIFETIME | 300 seconds |
| ROUTE_RREQ_WAIT_TIME | 2 seconds |
| UNICAST_MESSAGE_SENT_TIMEOUT | 1 second |
| RREQ_HOLDDOWN_TIME | 10 seconds |
+------------------------------+-------------+
Table 3: Default 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 for the
network where AODVv2 is used. Ideally, for networks with frequent
topology changes the AODVv2 parameters should be adjusted using
either experimentally determined values or dynamic adaptation. For
example, in networks with infrequent topology changes MAX_IDLETIME
may be set to a much larger value.
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+------------------------+-----------+------------------------------+
| Name | Value | Description |
+------------------------+-----------+------------------------------+
| MAX_HOPCOUNT | 20 hops | This value MUST be larger |
| | | than the AODVv2 network |
| | | diameter. Otherwise, |
| | | routing messages may not |
| | | reach their intended |
| | | destinations. |
| MAX_METRIC[i] | Not | If defined, this is the |
| | Specified | maximum permissible value |
| | in This | for Metric Type 'i' (see |
| | Document | [RFC6551]). |
| MAXTIME | TBD | The maximum expressible |
| | | value for clock time. |
| DISCOVERY_ATTEMPTS_MAX | 3 | The number of route |
| | | discovery attempts to make |
| | | before indicating that a |
| | | particular address is not |
| | | reachable. |
| MTU | TBD -- | Determines the maximum |
| | depends | number of RFC 5444 AddrBlk |
| | on | entries |
| | address | |
| | family | |
+------------------------+-----------+------------------------------+
Table 4: Default Parameter Values
In addition to the above parameters and timing values, several
administrative options exist. These options have no influence on
correct routing behavior, although they may potentially reduce AODVv2
protocol messaging in certain situations. The default behavior is to
NOT enable any of these options; and although many of these options
can be administratively controlled, they may be better served by
intelligent control. The following table enumerates several of the
options.
+-------------------------+-----------------------------------------+
| Name | Description |
+-------------------------+-----------------------------------------+
| APPEND_INFORMATION | Whether or not appending routing |
| | information for AddedNodes to a RteMsg |
| | is enabled. |
| BUFFER_SIZE_PACKETS | 2 |
| BUFFER_SIZE_BYTES | MAX_PACKET_SIZE [TBD] |
| APPEND_IDLE_UNREACHABLE | Whether to append Unreachable |
| | information about idle routes to RERR. |
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| CONTROL_TRAFFIC_LIMIT | TBD [50 msgs/sec?] |
+-------------------------+-----------------------------------------+
Table 5: Administratively Controlled Options
Note: several fields have limited size (bits or bytes). These sizes
and their encoding may place specific limitations on the values that
can be set. For example, MsgHdr.<msg-hop-count> is a 8-bit field and
therefore MAX_HOPCOUNT cannot be larger than 255.
15. IANA Considerations
This section specifies several message types, message tlv-types, and
address tlv-types. Also, a new registry of 16-bit alternate metric
types is specified.
15.1. AODVv2 Message Types Specification
+----------------------------------------+----------+
| Name | Type |
+----------------------------------------+----------+
| Route Request (RREQ) | 10 - TBD |
| Route Reply (RREP) | 11 - TBD |
| Route Error (RERR) | 12 - TBD |
| Route Reply Acknowledgement (RREP_ACK) | 13 - TBD |
+----------------------------------------+----------+
Table 6: AODVv2 Message Types
15.2. Message and Address Block TLV Type Specification
+-------------------+------+--------+-------------------------------+
| Name | Type | Length | Value |
+-------------------+------+--------+-------------------------------+
| Unicast Response | 10 - | 0 | Indicates to the handling |
| Request (RespReq) | TBD | octets | (receiving) AODVv2 router |
| | | | that the previous hop |
| | | | (IP.SourceAddress) expects a |
| | | | unicast reply message within |
| | | | UNICAST_MESSAGE_SENT_TIMEOUT. |
| | | | -- |
| Destination RREP | 11 - | 0 | Indicates that intermediate |
| Only (DestOnly) | TBD | octets | RREPs are prohibited. |
| | | | -- |
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| Packet source IP | 12 - | 4 or | Provides the IP address for |
| address | TBD | 16 | RERR messages generated due |
| (PktSource) | | octets | to inability to deliver a |
| | | | packet. |
| | | | -- |
| Metric Type | 13 - | 1 | Type of metric in the Metric8 |
| | TBD | octet | or Metric16 AddrTLV. |
+-------------------+------+--------+-------------------------------+
Table 7: Message TLV Types
15.3. Address Block TLV Specification
+---------------+------------+----------+---------------------------+
| Name | Type | Length | Value |
+---------------+------------+----------+---------------------------+
| VALIDITY_TIME | 1[RFC5497] | 1 octet | The maximum amount of |
| | | | time that information can |
| | | | be maintained before |
| | | | being deleted. The |
| | | | VALIDITY_TIME TLV is |
| | | | defined in [RFC5497]. |
| | | | -- |
| Sequence | 10 - TBD | 2 octets | The latest AODVv2 |
| Number | | | sequence number |
| (SeqNum) | | | associated with the |
| | | | address. |
| Metric8 | 11 - TBD | 1 octet | 8-bit Cost of the route |
| | | | to reach the destination |
| | | | address. |
| Metric16 | 12 - TBD | 2 octets | 16-bit Cost of the route |
| | | | to reach the destination |
| | | | address. |
+---------------+------------+----------+---------------------------+
Table 8: Address Block TLV (AddrTLV) Types
The same number space should be used for both Metric8 and Metric16
metric types.
15.4. Metric Type Number Allocation
Metric types are identified according to the assignments as specified
in [RFC6551]. The metric type of the Hop Count metric is assigned to
be 3, in order to maintain compatibility with that existing table of
values from RFC 6551. If non-additive metrics are to be used, the
specification for assessing the usability of route updates (see
Section 6.1 ) may require changes.
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+-----------------------+----------+-----------+
| Name | Type | Size |
+-----------------------+----------+-----------+
| Reserved | 0 | Undefined |
| Unallocated | 1 -- 2 | TBD |
| Hop Count | 3 - TBD | 1 octet |
| Unallocated | 4 -- 254 | TBD |
| Reserved | 255 | Undefined |
+-----------------------+----------+-----------+
Table 9: Metric Types
16. Security Considerations
The objective of the AODVv2 protocol is for each router to
communicate reachability information about addresses for which it is
responsible. Positive routing information (i.e. a route exists) is
distributed via RteMsgs and negative routing information (i.e. a
route does not exist) via RERRs. AODVv2 routers that handle these
messages store the contained information to properly forward data
packets, and they generally provide this information to other AODVv2
routers.
This section does not mandate any specific security measures.
Instead, this section describes various security considerations and
potential avenues to secure AODVv2 routing.
The most important security mechanisms for AODVv2 routing are
integrity/authentication and confidentiality.
In situations where routing information or router identity are
suspect, integrity and authentication techniques SHOULD be applied to
AODVv2 messages. In these situations, routing information that is
distributed over multiple hops SHOULD also verify the integrity and
identity of information based on originator of the routing
information.
A digital signature could be used to identify the source of AODVv2
messages and information, along with its authenticity. A nonce or
timestamp SHOULD also be used to protect against replay attacks.
S/MIME and OpenPGP are two authentication/integrity protocols that
could be adapted for this purpose.
In situations where confidentiality of AODVv2 messages is important,
cryptographic techniques can be applied.
In certain situations, for example sending a RREP or RERR, an AODVv2
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router could include proof that it has previously received valid
routing information to reach the destination, at one point of time in
the past. In situations where routers are suspected of transmitting
maliciously erroneous information, the original routing information
along with its security credentials SHOULD be included.
Note that if multicast is used, any confidentiality and integrity
algorithms used MUST permit multiple receivers to handle the message.
Routing protocols, however, are prime targets for impersonation
attacks. In networks where the node membership is not known, it is
difficult to determine the occurrence of impersonation attacks, and
security prevention techniques are difficult at best. However, when
the network membership is known and there is a danger of such
attacks, AODVv2 messages must be protected by the use of
authentication techniques, such as those involving generation of
unforgeable and cryptographically strong message digests or digital
signatures. While AODVv2 does not place restrictions on the
authentication mechanism used for this purpose, IPsec Authentication
Message (AH) is an appropriate choice for cases where the nodes share
an appropriate security association that enables the use of AH.
In particular, routing messages SHOULD be authenticated to avoid
creation of spurious routes to a destination. Otherwise, an attacker
could masquerade as that destination and maliciously deny service to
the destination and/or maliciously inspect and consume traffic
intended for delivery to the destination. RERR messages SHOULD be
authenticated in order to prevent malicious nodes from disrupting
active routes between communicating nodes.
If the mobile nodes in the ad hoc network have pre-established
security associations, the purposes for which the security
associations are created should include that of authorizing the
processing of AODVv2 control packets. Given this understanding, the
mobile nodes should be able to use the same authentication mechanisms
based on their IP addresses as they would have used otherwise.
If the mobile nodes in the ad hoc network have pre-established
security associations, the purposes for which the security
associations Most AODVv2 messages are transmitted to the multicast
address LL-MANET-Routers [RFC5498]. It is therefore required for
security that AODVv2 neighbors exchange security information that can
be used to insert an ICV [RFC6621] into the AODVv2 message block
[RFC5444]. This enables hop-by-hop security, which is proper for
these message types that may have mutable fields. For destination-
only RREP discovery procedures, AODVv2 routers that share a security
association SHOULD use the appropriate mechanisms as specified in RFC
6621. The establishment of these security associations is out of
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scope for this document.
17. 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-Royer for
her long time authorship of AODV. Additional thanks to Luke Klein-
Berndt, Pedro Ruiz, Fransisco Ros, Henning Rogge, Koojana
Kuladinithi, Ramon Caceres, Thomas Clausen, Christopher Dearlove,
Seung Yi, Romain Thouvenin, Tronje Krop, Henner Jakob, Alexandru
Petrescu, Christoph Sommer, Cong Yuan, Lars Kristensen, and Derek
Atkins for reviewing of AODVv2, as well as several specification
suggestions.
This revision of AODVv2 separates the minimal base specification from
other optional features to expedite the process of assuring
compatibility with the existing LOADng specification
[I-D.clausen-lln-loadng] (minimal reactive routing protocol
specification). Thanks are due to T. Clausen, A. Colin de Verdiere,
J. Yi, A. Niktash, Y. Igarashi, Satoh. H., and U. Herberg for their
development of LOADng and sharing details for assuring
appropriateness of AODVv2 for their application.
18. References
18.1. Normative References
[RFC1812] Baker, F., "Requirements for IP Version 4 Routers",
RFC 1812, June 1995.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC5082] Gill, V., Heasley, J., Meyer, D., Savola, P., and C.
Pignataro, "The Generalized TTL Security Mechanism
(GTSM)", RFC 5082, October 2007.
[RFC5444] Clausen, T., Dearlove, C., Dean, J., and C. Adjih,
"Generalized Mobile Ad Hoc Network (MANET) Packet/Message
Format", RFC 5444, February 2009.
[RFC5497] Clausen, T. and C. Dearlove, "Representing Multi-Value
Time in Mobile Ad Hoc Networks (MANETs)", RFC 5497,
March 2009.
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[RFC5498] Chakeres, I., "IANA Allocations for Mobile Ad Hoc Network
(MANET) Protocols", RFC 5498, March 2009.
[RFC6551] Vasseur, JP., Kim, M., Pister, K., Dejean, N., and D.
Barthel, "Routing Metrics Used for Path Calculation in
Low-Power and Lossy Networks", RFC 6551, March 2012.
18.2. Informative References
[I-D.clausen-lln-loadng]
Clausen, T., Verdiere, A., Yi, J., Niktash, A., Igarashi,
Y., Satoh, H., Herberg, U., Lavenu, C., Lys, T., Perkins,
C., and J. Dean, "The Lightweight On-demand Ad hoc
Distance-vector Routing Protocol - Next Generation
(LOADng)", draft-clausen-lln-loadng-06 (work in progress),
October 2012.
[I-D.perkins-irrep]
Perkins, C. and I. Chakeres, "Intermediate RREP for
dynamic MANET On-demand (AODVv2) Routing",
draft-perkins-irrep-02 (work in progress), November 2012.
[Perkins99]
Perkins, C. and E. Belding-Royer, "Ad hoc On-Demand
Distance Vector (AODV) Routing", Proceedings of the 2nd
IEEE Workshop on Mobile Computing Systems and
Applications, New Orleans, LA, pp. 90-100, February 1999.
[RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328, April 1998.
[RFC2501] Corson, M. and J. Macker, "Mobile Ad hoc Networking
(MANET): Routing Protocol Performance Issues and
Evaluation Considerations", RFC 2501, January 1999.
[RFC3561] Perkins, C., Belding-Royer, E., and S. Das, "Ad hoc On-
Demand Distance Vector (AODV) Routing", RFC 3561,
July 2003.
[RFC4193] Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast
Addresses", RFC 4193, October 2005.
[RFC4728] Johnson, D., Hu, Y., and D. Maltz, "The Dynamic Source
Routing Protocol (DSR) for Mobile Ad Hoc Networks for
IPv4", RFC 4728, February 2007.
[RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
"Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
September 2007.
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[RFC5148] Clausen, T., Dearlove, C., and B. Adamson, "Jitter
Considerations in Mobile Ad Hoc Networks (MANETs)",
RFC 5148, February 2008.
[RFC5340] Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF
for IPv6", RFC 5340, July 2008.
[RFC6130] Clausen, T., Dearlove, C., and J. Dean, "Mobile Ad Hoc
Network (MANET) Neighborhood Discovery Protocol (NHDP)",
RFC 6130, April 2011.
[RFC6549] Lindem, A., Roy, A., and S. Mirtorabi, "OSPFv2 Multi-
Instance Extensions", RFC 6549, March 2012.
[RFC6621] Macker, J., "Simplified Multicast Forwarding", RFC 6621,
May 2012.
Appendix A. Example RFC 5444-compliant packet formats
The following three subsections show example RFC 5444-compliant
packets for AODVv2 message types RREQ, RREP, and RERR. These
proposed message formats are designed based on expected savings from
IPv6 addressable MANET nodes, and a layout for the Address TLVs that
may be viewed as natural, even if perhaps not the absolute most
compact possible encoding.
For RteMsgs, the msg-hdr fields are followed by at least one and
optionally two Address Blocks. The first AddrBlk contains OrigNode
and TargNode. For each AddrBlk, there must be AddrTLVs of type
Seqnum and of type Metric.
In addition to the Seqnum TLV, there MUST be an AddrTLV of type
Metric. The msg-hop-count is counts the number of hops followed by
the RteMsg from RteMsg_Orig to the current intermediate AODVv2 router
handling the RteMsg. Alternate metrics are enabled by the inclusion
of the MetricType MsgTLV. When there is no such MetricType MsgTLV
present, then the Metric AddrTLV measures HopCount. The Metric
AddrTLV also provides a way for the RteMsg_Orig to supply an initial
nonzero cost for the route between the RteMsg_Orig and its client
node, i.e., either OrigNode or TargNode.
AddedNode information MAY be included in a RteMsg by adding a second
AddrBlk. Both Metric AddrTLVs use the same Metric Type.
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A.1. RREQ Message Format
The figure below illustrates a packet format for an example RREQ
message.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PV=0 | PF=0 | msg-type=RREQ | MF=4 | MAL=3 | msg-size=24 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| msg-size=24 | msg-hop-limit | msg.tlvs-length=0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| num-addr=2 |1|0|0|0|0| Rsv | head-length=3 |Head(Orig&Targ)|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Head (bytes for Orig & Target)| Orig.Tail | Target.Tail |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| addr.tlvs-length=11 | type=SeqNum |0|1|0|1|0|0|Rsv|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Index-start=0 | tlv-length=2 | Orig.Node Sequence # |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| type=SeqNum |0|1|0|1|0|0|Rsv| Index-start=0 | tlv-length=1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OrigNodeHopCt |
+-+-+-+-+-+-+-+-+
RREQ with SeqNum and Metric AddrTLVs added, and: - two addresses in
Address Block - address length = 4 [IPv4], shared initial bytes = 3 -
Sequence Number available only for Orig.Node in addr.tlv - Hop Count
available only for Orig.Node in Metric8 AddrTLV - Addresses stored in
the order OrigNode, TargNode
Figure 4: Example IPv4 RREQ
A.2. RREP Message Format
The figure below illustrates a packet format for an example RREP
message.
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PV=0 | PF=0 | msg-type=RREP | MF=4 | MAL=3 | msg-size=30 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| msg-size=30 | msg-hop-limit | msg.tlvs-length=0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| num-addr=2 |1|0|0|0|0| Rsv | head-length=3 |Head(Orig&Targ)|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Head (bytes for Orig & Target)| Orig.Tail | Target.Tail |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| addr.tlvs-length=13 | type=SeqNum |0|1|0|1|0|0|Rsv|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Index-start=0 | tlv-length=2 | Orig.Node Sequence # |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Target.Node Sequence # | type=Metric8 |0|1|0|1|0|0|Rsv|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Index-start=1 | tlv-length=1 | TargNodeHopCt |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
RREP with SeqNum and Metric AddrTLVs added, and: - two addresses in
AddrBlk - address length = 4 [IPv4], shared initial bytes = 3 - One
Sequence Number (for TargNode) in SeqNum AddrTLV - Hop Count
available only for Targ.Node in Metric8 AddrTLV - Addresses stored in
the order OrigNode, TargNode
Figure 5: Example IPv4 RREP
A.3. RERR Message Format
The figure below illustrates a packet format for an example RERR
message.
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PV=0 | PF=0 | msg-type=RERR | MF=4 | MAL=3 | msg-size=25 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| msg-size=25 | msg-hop-limit | msg.tlvs-length=0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| num-addr=2 |1|0|0|0|0| Rsv | head-length=3 |Head(Two Dests)|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Head (for both destinations) | Tail(Dest_1) | Tail(Dest_2) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| addr.tlvs-length=8 | type=SeqNum |0|1|0|1|0|0|Rsv|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Index-start=0 | tlv-length=2 | Dest_1 Sequence # |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Dest_2 Sequence # |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
RERR with - Two Unreachable Node address in Address Block - address
length = 4 [IPv4], shared initial bytes = 3 - Two Sequence Numbers
available in addr.tlv - Addresses stored from Originator to Target
Figure 6: Example IPv4 RERR
A.4. RREP_ACK Message Format
The figure below illustrates a packet format for an example RREP_ACK
message.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PV=0 | PF=0 |msg-type=RREPAk| MF=0 | MAL=3 | msg-size=3 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| msg-size=3 |
+-+-+-+-+-+-+-+-+
RREP_ACK - address length = 4 [IPv4]
Figure 7: Example IPv4 RREP_ACK
Appendix B. Changes since revision ...-21.txt
The revisions of this document that were numbered 22 and 23 were
produced without sufficient time for preparation, and suffered from
numerous editorial errors. Therefore, this list of changes is
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enumerated based on differences between this revision (24) and
revision 21.
o Alternate metrics enabled:
* New section added to describe general design approach.
* Abstract functions "Cost()" and "LoopFree()" defined.
* MAX_HOPCOUNT typically replaced by MAX_METRIC.
* DEFAULT_METRIC_TYPE parameter defined, defaulting to HopCount.
* MetricType MsgTLV defined.
* Metric8 and Metric16 AddrTLVs defined.
o Many changes for RFC 5444 compliance
o New section added for "Notational Conventions" (see Table 1).
Many changes to improve readability and accuracy (e.g., eliminate
use of "Flooding", "ThisNode", ...).
o Reorganized and simplified route lifetime management (see
Section 5.1).
o Reorganized document structure, combining closely related small
sections and eliminating top-level "Detailed ..." section.
* RREQ and RREP specification sections coalesced.
* RERR specification sections coalesced.
* Eliminated resulting duplicated specification.
* New section added for "Notational Conventions".
o Internet-Facing AODVv2 router renamed to be IAR
o "Optional Features" section (see Section 13) created to contain
features not required within base specification, including:
* Adding RREP-ACK message type instead of relying on reception of
arbitrary packets as sufficient response to establish
bidirectionality.
* Expanding Rings Multicast
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* Intermediate RREPs (iRREPs): Without iRREP, only the
destination can respond to a RREQ.
* Precursor lists.
* Reporting Multiple Unreachable Nodes. An RERR message can
carry more than one Unreachable Destination node for cases when
a single link breakage causes multiple destinations to become
unreachable from an intermediate router.
* Message Aggregation.
* Inclusion of Added Routing Information.
o Sequence number MUST be incremented after generating any RteMsg.
o Resulting simplifications for accepting route updates in RteMsgs.
o Sequence number MUST (instead of SHOULD) be set to 1 after
rollover.
o AODVv2 routers MUST (instead of SHOULD) only handle AODVv2
messages from adjacent routers.
o Clarification that Added Routing information in RteMsgs is
optional (MAY) to use.
o Clarification that if Added Routing information in RteMsgs is
used, then the Route Table Entry SHOULD be updated using normal
procedures as described in Section 6.2.
o Clarification in Section 7.1 that nodes may be configured to
buffer zero packets.
o Clarification in Section 7.1 that buffered packets MUST be dropped
if route discovery fails.
o In Section 8.2, relax mandate for monitoring connectivity to next-
hop AODVv2 neighbors (from MUST to SHOULD), in order to allow for
minimal implementations
o Remove Route.Forwarding flag; identical to "NOT" Route.Broken.
o Routing Messages MUST be originated with the MsgHdr.<msg-hop-
limit> set to MAX_HOPCOUNT.
o Maximum hop count set to MAX_HOPCOUNT, and 255 is reserved for
"unknown". Since the current draft only uses hop-count as
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distance, this is also the current maximum distance.
Appendix C. Shifting Network Prefix Advertisement Between AODVv2
Routers
Only one AODVv2 router within a MANET SHOULD be responsible for a
particular address at any time. If two AODVv2 routers dynamically
shift the advertisement of a network prefix, correct AODVv2 routing
behavior must be observed. The AODVv2 router adding the new network
prefix must wait for any existing routing information about this
network prefix to be purged from the network. Therefore, it must
wait at least ROUTER_SEQNUM_AGE_MAX_TIMEOUT after the previous AODVv2
router for this address stopped advertising routing information on
its behalf.
Authors' Addresses
Charles E. Perkins
Futurewei Inc.
2330 Central Expressway
Santa Clara, CA 95050
USA
Phone: +1-408-330-5305
Email: charliep@computer.org
Ian D Chakeres
CenGen
9250 Bendix Road North
Columbia, Maryland 21045
USA
Email: ian.chakeres@gmail.com
URI: http://www.ianchak.com/
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