Mobile Ad Hoc Networking Working Group Elizabeth M. Belding-Royer
INTERNET DRAFT Yuan Sun
14 November 2001 University of California, Santa Barbara
Charles E. Perkins
Nokia Research Center
Global Connectivity for IPv4 Mobile Ad hoc Networks
draft-royer-manet-globalv4-00.txt
Status of This Memo
This document is a submission by the Mobile Ad Hoc Networking Working
Group of the Internet Engineering Task Force (IETF). Comments should
be submitted to the manet@itd.nrl.navy.mil mailing list.
Distribution of this memo is unlimited.
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026. Internet-Drafts are working
documents of the Internet Engineering Task Force (IETF), its areas,
and its working groups. Note that other groups may also distribute
working documents as Internet-Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at
any time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at:
http://www.ietf.org/ietf/1id-abstracts.txt
The list of Internet-Draft Shadow Directories can be accessed at:
http://www.ietf.org/shadow.html.
Abstract
This document describes how to provide Internet connectivity to
mobile ad hoc networks. It describes a mechanism whereby the Ad
hoc On-Demand Distance Vector (AODV) Routing protocol can cooperate
with the Mobile IP protocol such that mobile nodes within an ad hoc
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network, which are out of direct transmission range of a foreign
agent, can obtain a care-of address and register with the foreign
agent to obtain Internet connectivity. Mobile IP is used for mobile
node registrations with a foreign agent, while AODV is used for
routing within the ad hoc network and for obtaining routes to the
foreign agent. Once a manet node has a care-of address, it may send
data packets to destinations in the Internet by routing through the
foreign agent.
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Contents
Status of This Memo i
Abstract i
1. Introduction 1
2. Terminology 1
3. Overview 1
4. Packet Formats 2
4.1. Route Reply (RREP) Message Format . . . . . . . . . . . . 3
5. Addressing 4
5.1. Foreign Agent Discovery . . . . . . . . . . . . . . . . . 5
6. Internet Connectivity 6
6.1. Agent Advertisements . . . . . . . . . . . . . . . . . . 6
6.2. Registering with the Foreign Agent . . . . . . . . . . . 7
6.3. Route Discovery . . . . . . . . . . . . . . . . . . . . . 7
7. Extension Formats 9
7.1. RREP Foreign Agent Extension Format . . . . . . . . . . . 10
8. Configuration Parameters 10
9. Security Considerations 11
10. Acknowledgments 11
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1. Introduction
A mobile ad hoc network (manet) is the cooperative engagement
of a collection of (typically wireless) mobile nodes without the
required intervention of any centralized access point or existing
infrastructure. Many routing protocols have been proposed for
discovering and maintaining routes within these networks. The Ad hoc
On-Demand Distance Vector (AODV) Routing protocol [4] is one such
protocol. AODV builds and maintains a route between a source and
destination pair despite route path changes due to movement of nodes.
Global connectivity is required for mobile nodes to communicate with
the fixed Internet. However, routing protocols for ad hoc networks
typically only maintain routes within the ad hoc network, and hence
do not provide a way to utilize an access point to the wired network
when one is available. In particular, mobile nodes that are multiple
hops away from a foreign agent are unable to utilize that foreign
agent for obtaining a care-of address and global connectivity.
This document specifies a method for enabling ad hoc networks to
utilize connectivity to the Internet, whenever such a connection is
available. Specifically, a method for cooperation of the Mobile
IP [3] and AODV protocols is proposed, such that mobile nodes may
obtain a care-of address and access the global Internet, even when
they are multiple hops away from the access point.
2. Terminology
This protocol specification uses conventional meanings [1] for
capitalized words such as MUST, SHOULD, etc., to indicate requirement
levels for various protocol features.
3. Overview
This document proposes a method whereby an ad hoc network of mobile
nodes can obtain Internet connectivity when one or more of the mobile
nodes is within transmission range of a MobileIP foreign agent.
The proposed method utilizes the Ad hoc On-Demand Distance Vector
(AODV) Routing protocol for the discovery and maintenance of routes
within the ad hoc network. The Mobile IP protocol is utilized such
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that mobile nodes may obtain care-of addresses, and hence Internet
connectivity, through a multi-hop path to a foreign agent.
Agent Advertisement messages initiated by foreign agents are
rebroadcast by the nodes within the ad hoc network so that mobile
nodes may learn of the presence of the foreign agent. Alternatively,
mobile nodes may proactively discover foreign agents by issuing
a Route Request for the ``All Mobility Agents'' multicast group
address. Mobile nodes with a current route to a foreign agent
unicast a Route Reply to the requesting node, indicating the IP
address of the foreign agent. Upon reception of this message, the
mobile may unicast an Agent Solicitation message to the foreign
agent.
Foreign agents are used by the mobile nodes to acquire care-of
addresses for global Internet connectivity. Once a route to a
foreign agent is known, a mobile node unicasts a Registration Request
message to the foreign agent, thereby registering with that foreign
agent and its home agent.
Route discovery within the ad hoc network is accomplished through
AODV's route request/route reply discovery cycle. Destinations
that are not members of the ad hoc network can be reached through
the foreign agent. Upon reception of Route Request messages for
destinations within the wired Internet, the foreign agent transmits a
route reply to the requesting node, indicating that the destination
node can be reached through the foreign agent.
The methods proposed in this document conform to the MobileIP
protocol specified in [3] and the AODV protocol specified in [4].
All message types, data structures, and configuration parameters
specified within these documents are used unmodified, unless
otherwise noted.
4. Packet Formats
All packet formats are the same as in [4], unless otherwise
specified.
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4.1. Route Reply (RREP) Message Format
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type |R|A|F| Reserved |Prefix Sz| Hop Count |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Destination IP address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Destination Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Source IP address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The format of the Route Reply message is illustrated above, and
contains the following fields:
Type 2
R Repair flag; used for multicast.
A Acknowledgment required.
F Foreign Agent RREP (FA-RREP); see section 6.3
Reserved Sent as 0; ignored on reception.
Prefix Size If nonzero, the 5-bit Prefix Size specifies that the
indicated next hop may be used for any nodes with
the same routing prefix (as defined by the Prefix
Size) as the requested destination.
Hop Count The number of hops from the Source IP Address to
the Destination IP Address. For multicast route
requests this indicates the number of hops to the
multicast tree member sending the RREP.
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Destination IP Address
The IP address of the destination for which a route
is supplied.
Destination Sequence Number
The destination sequence number associated to the
route.
Source IP Address
The IP address of the source node which issued the
RREQ for which the route is supplied.
Lifetime The time for which nodes receiving the RREP consider
the route to be valid.
Note that this RREP is the same message type as the RREP in [4], with
the addition of the 'F' flag to indicate that the RREP is an FA-RREP
sent by the foreign agent (section 6.3).
5. Addressing
A node that desires Internet connectivity must have a globally
routable IP address. When a node has an IP address that is valid on
its home network, normal Mobile IP operation applies; the node must
obtain a care-of address on the visited network to obtain Internet
connectivity. The node may obtain such an address in one of three
ways:
(i) It may wait for the reception of an Agent Advertisement message,
initiated by the foreign agent.
(ii) It may proactively request an address by issuing an Agent
Solicitation message for the foreign agent.
(iii) It may acquire a co-located care-of address through some external
means.
Foreign agents periodically transmit Agent Advertisement messages on
their wireless channels. These messages contain the IP address of
the foreign agent. Optionally, these messages may also contain one
or more advertised Care-of Addresses. When a mobile node receives
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such an advertisement, it selects one of the advertised care-of
addresses to be its new care-of address.
Alternatively, according to (ii) above, a node may proactively
solicit a care-of address from a foreign agent by issuing an Agent
Solicitation. A mobile node that does not know the IP address of
any foreign agents must discover a route to its closest foreign
agent. It is possible for a mobile node to not have received an
Agent Advertisement if the node has just joined the network and is in
the interval between Agent Advertisements, or if network collisions
prevented the broadcast Agent Advertisement from reaching the mobile.
Section 5.1 describes the foreign agent discovery procedure.
Finally, a node may obtain a co-located care-of address through some
external means, such as through a DHCP server. The specific means of
obtaining a co-located care-of address are beyond the scope of this
document.
5.1. Foreign Agent Discovery
When a mobile node wishes to proactively discover a foreign agent,
it may do so by issuing a Route Request (RREQ). This RREQ is a
standard RREQ message, as specified in [4], that has the destination
IP address set to 224.0.0.11, the ``All Mobility Agents'' multicast
group address [2]. The mobile cannot put the IP address of the
foreign agent into the RREQ because it may not know the FA's address.
The mobile node then broadcasts this RREQ to its neighbors.
When a neighboring mobile node receives this RREQ, it first
checks its Foreign Agent List to determine whether it is currently
registered with a foreign agent. If the node is not running
MobileIP, then it does not have a Foreign Agent List, and so it
simply rebroadcasts the request. Also, if the mobile node is not
registered with any foreign agents, then it likewise rebroadcasts
the request. If, on the other hand, the mobile node is currently
registered with a foreign agent, then the mobile checks whether it
has a current route to that foreign agent. It is possible for the
node to be registered with a foreign agent while its route to that
agent has expired or been invalidated. If the mobile node does not
have a current route to the foreign agent, then it rebroadcasts the
request. Otherwise, if it does have a current route to the foreign
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agent, it creates a route reply as specified in section 8.6 of [4],
with the exception that it appends a Foreign Agent extension to the
RREP. The format of the extension is given in section 7.1. The
Foreign Agent extension indicates the IP address of the foreign
agent. The agent's IP address is placed in the ForeignAgent IP
Address field of the RREP extension. The foreign agent group IP
address (224.0.0.11) is placed in the Destination IP Address field of
the RREP. The RREP is then unicast back to the source node.
When the source node receives a route reply for a foreign agent, it
can then use that route to unicast an Agent Solicitation message to
the foreign agent. Note that the TTL of this Agent Solicitation MUST
NOT be set to 1, as specified in [3]. Instead, the TTL should be set
equal to NETWORK_DIAMETER, so that the foreign agent is ensured of
receiving the Solicitation. Upon receiving the Agent Solicitation
message, the foreign agent unicasts an Agent Advertisement back to
the mobile node.
After receiving the Agent Advertisement message, the mobile node then
proceeds as described in the previous section, by selecting one of
the advertised care-of addresses to be its own care-of address.
6. Internet Connectivity
6.1. Agent Advertisements
Foreign agents periodically advertise their presence through Agent
Advertisement messages. The Agent Advertisement messages are
constructed as described in section 2.1 of [3].
When mobile nodes receive the Agent Advertisement, they process
it according to section 2.4 in [3]. In addition, the mobile node
records the foreign agent IP address, together with the Sequence
Number of the Agent Advertisement. In this way, if it later receives
the packet as it is rebroadcast by its neighbors, it will know not
to reprocess the packet. When a node receives duplicate Agent
Advertisement messages, it silently discards those duplicates.
After processing the Agent Advertisement, the mobile node MUST
rebroadcast the packet on its interfaces. This allows mobile nodes
that are not in direct communication range of the foreign agent to
receive the Agent Advertisements. The rebroadcasting of the Agent
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Advertisement message SHOULD be slightly randomized in order to
avoid synchronization and subsequent collisions with other nodes'
rebroadcasts.
6.2. Registering with the Foreign Agent
When a mobile node receives an Agent Advertisement with the 'R'
bit set, the mobile node MUST register with the foreign agent, as
specified in section 2.4.1 of [3]. If the mobile node receives an
Agent Advertisement without the 'R' bit set, then it MUST register
with the foreign agent if it requires Internet connectivity.
To register with the foreign agent after receiving an Agent
Advertisement, the node creates a Registration Request and fills in
the fields of the Registration Request as indicated in section 3.3
of [3]. The node then unicasts the Registration Request message to
the foreign agent. The node should have a valid path to the foreign
agent because it has just received an Agent Advertisement from the
agent. In the event that the mobile node's route to the foreign
agent has become invalid, the node can initiate a route discovery
procedure to find a new route to the foreign agent. It can then use
that route for the transmission of the Registration Request.
The foreign agent processes the Registration Request as specified
in [3], with the exception that, when it receives the Registration
Reply from the home agent, it unicasts this Reply along the
(possibly) multi-hop path back to the mobile node. Upon reception of
the Registration Reply, if the foreign agent's route to the mobile
node has timed out or been invalidated, the foreign agent must
discover a route to the mobile node. For instance, it may use the
route discovery procedure described in [4].
6.3. Route Discovery
A mobile node that needs a route to a destination does not initially
know whether the destination node is within the ad hoc network, or
whether it is reachable through the wired interface of the foreign
agent. It therefore must first search the ad hoc network for the
destination. If a route to the destination is not discovered within
the ad hoc network, the mobile can conclude that the destination is
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not in the ad hoc network, and hence it can use the foreign agent
as a default router and send the data packets for the destination
directly to the foreign agent.
To begin the search for the destination, the mobile node creates
a route request for the destination, as specified in section 8.3
of [4]. At the mobile nodes, the route request is processed and
route replies are generated as specified in [4] as well.
The foreign agent has specialized processing of route request
messages. When a foreign agent receives a route request, it checks
its route table to determine whether it has an explicit route entry
for the destination node. The foreign agent may have such an entry
if the destination is a registered mobile node within the ad hoc
network. If a valid route table entry for the destination exists,
then the foreign agent creates a route reply as specified in [4].
On the other hand, if the foreign agent does not have a route table
entry for the destination node, then it assumes that the destination
is a node in the Internet that is reachable through its wired
interface. In this case, it creates a special route reply with the
'F' flag set. The destination sequence number of the RREP is set
equal to that in the RREQ, and the hopcount of the RREP is set equal
to zero. The foreign agent then unicasts this route reply back to
the source node. This route reply is hereafter referred to as an
FA-RREP.
The mobile node waits NET_TRAVERSAL_TIME milliseconds for the
reception of a route reply. If it receives a route reply in response
to its route request that does not have the 'F' flag set, this
indicates the destination is in the ad hoc network and can be routed
to within the network. Once the route reply is received, the mobile
node can use the discovered path for data packet transmission to the
destination.
When the mobile node receives an FA-RREP, it stores this route but it
SHOULD NOT use this route immediately. This route reply indicates
that the foreign agent believes the destination node is located in
the wired Internet. It is possible for the mobile to receive an
FA-RREP from the foreign agent before it receives a route reply from
the destination node within the ad hoc network, if the mobile node is
located closer to the foreign agent than it is to the destination.
Therefore, the mobile node should retain this route, and only utilize
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it after it has concluded that the destination is not located in the
ad hoc network.
If a route reply without the 'F' flag set is not received after
NET_TRAVERSAL_TIME milliseconds, the mobile node attempts route
discovery up to RREQ_RETRIES additional times. If, after that number
of attempts, a route to the destination is not discovered, it is
concluded that the destination node is not in the ad hoc network.
The mobile node then determines whether it has received an FA-RREP in
response to its route request. If it has, it then enters this route
into its route table, and utilizes it for the transmission of data
packets to the destination node. These data packets are transmitted
using normal IP forwarding to the foreign agent. Once the foreign
agent receives the data packets, it also uses normal IP forwarding
to route the data packets to their intended destinations. Note that
tunneling within the ad hoc network is not needed.
7. Extension Formats
RREQ and RREP messages have extensions defined in the following
format:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | type-specific data ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
Type x
Length The length of the type-specific data, not including the
Type and Length fields of the extension.
Extensions with types between 128 and 255 may NOT be skipped. The
rules for extensions will be spelled out more fully, and conform with
the rules for handling IPv6 options.
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7.1. RREP Foreign Agent Extension Format
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Foreign Agent IP Address.... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ...FA IP Addr |
+-+-+-+-+-+-+-+-+
Type 10
Foreign Agent IP Address
IP Address of the foreign agent.
The Foreign Agent RREP extension is included during a route discovery
for foreign agents, when the source node does not know the IP address
of any foreign agents.
8. Configuration Parameters
This section gives default values for some important values
associated with address discovery protocol operations.
Parameter Name Value
---------------------- -----
NET_DIAMETER 10
NET_TRAVERSAL_TIME 3 * NODE_TRAVERSAL_TIME * NET_DIAMETER / 2
NODE_TRAVERSAL_TIME 40
RREQ_RETRIES 1
Note that the NET_TRAVERSAL_TIME and NODE_TRAVERSAL_TIME should be
set as specified in [4].
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9. Security Considerations
This document does not define any method for secure operation of the
protocol. While MobileIP provides mechanisms for securing mobile
node registrations, AODV does not currently provide any security
mechanisms. AODV is susceptible to impersonation attacks, as well as
malicious control packet modifications. The utilization of AODV with
MobileIP is subject to the same security attacks to which MobileIP
and AODV are already susceptible.
10. Acknowledgments
The authors would like to thank Jari Malinen and Ryuji Wakikawa
for their insightful comments which aided in the refinement of the
protocol design.
References
[1] S. Bradner. Key words for use in RFCs to Indicate Requirement
Levels. RFC 2119, March 1997.
[2] C. Perkins. IP Mobility Support. Request for Comments (Proposed
Standard) 2002, Internet Engineering Task Force, October 1996.
[3] Charles E. Perkins. IP Mobility Support for IPv4, Revised. IETF
Internet Draft, draft-ietf-mobileip-rfc2002-bis-08.txt, September
2001. (Work in Progress).
[4] Charles E. Perkins, Elizabeth M. Royer, and Samir R. Das. Ad hoc
On-Demand Distance Vector (AODV) Routing. IETF Internet Draft,
draft-ietf-manet-aodv-09.txt, November 2001. (Work in Progress).
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Author's Addresses
Questions about this memo can be directed to:
Elizabeth M. Belding-Royer
Dept. of Computer Science
University of California, Santa Barbara
Santa Barbara, CA 93106
+1 805 893 3411
+1 805 893 8553 (fax)
eroyer@cs.ucsb.edu
Yuan Sun
Dept. of Computer Science
University of California, Santa Barbara
Santa Barbara, CA 93106
+1 805 893 8981
+1 805 893 8553 (fax)
suny@cs.ucsb.edu
Charles E. Perkins
Communications Systems Laboratory
Nokia Research Center
313 Fairchild Drive
Mountain View, CA 94303
USA
+1 650 625 2986
+1 650 691 2170 (fax)
charliep@iprg.nokia.com
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