Network Working Group C. Perkins
Request for Comments: 3561 Nokia Research Center
Category: Experimental E. Belding-Royer
University of California, Santa Barbara
S. Das
University of Cincinnati
July 2003
Ad hoc On-Demand Distance Vector (AODV) Routing
Status of this Memo
This memo defines an Experimental Protocol for the Internet
community. It does not specify an Internet standard of any kind.
Discussion and suggestions for improvement are requested.
Distribution of this memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (2003). All Rights Reserved.
Abstract
The Ad hoc On-Demand Distance Vector (AODV) routing protocol is
intended for use by mobile nodes in an ad hoc network. It offers
quick adaptation to dynamic link conditions, low processing and
memory overhead, low network utilization, and determines unicast
routes to destinations within the ad hoc network. It uses
destination sequence numbers to ensure loop freedom at all times
(even in the face of anomalous delivery of routing control messages),
avoiding problems (such as "counting to infinity") associated with
classical distance vector protocols.
Table of Contents
1. Introduction ............................................... 2
2. Overview .................................................. 3
3. AODV Terminology ........................................... 4
4. Applicability Statement .................................... 6
5. Message Formats ............................................ 7
5.1. Route Request (RREQ) Message Format ................... 7
5.2. Route Reply (RREP) Message Format ..................... 8
5.3. Route Error (RERR) Message Format ..................... 10
5.4. Route Reply Acknowledgment (RREP-ACK) Message Format .. 11
6. AODV Operation ............................................. 11
6.1. Maintaining Sequence Numbers .......................... 11
6.2. Route Table Entries and Precursor Lists ............... 13
Perkins, et. al. Experimental [Page 1]
RFC 3561 AODV Routing July 2003
6.3. Generating Route Requests ............................. 14
6.4. Controlling Dissemination of Route Request Messages ... 15
6.5. Processing and Forwarding Route Requests .............. 16
6.6. Generating Route Replies .............................. 18
6.6.1. Route Reply Generation by the Destination ...... 18
6.6.2. Route Reply Generation by an Intermediate
Node ........................................... 19
6.6.3. Generating Gratuitous RREPs .................... 19
6.7. Receiving and Forwarding Route Replies ................ 20
6.8. Operation over Unidirectional Links ................... 21
6.9. Hello Messages ........................................ 22
6.10 Maintaining Local Connectivity ........................ 23
6.11 Route Error (RERR) Messages, Route Expiry and Route
Deletion .............................................. 24
6.12 Local Repair .......................................... 26
6.13 Actions After Reboot ................................. 27
6.14 Interfaces ............................................ 28
7. AODV and Aggregated Networks ............................... 28
8. Using AODV with Other Networks ............................. 29
9. Extensions ................................................. 30
9.1. Hello Interval Extension Format ....................... 30
10. Configuration Parameters ................................... 31
11. Security Considerations .................................... 33
12. IANA Considerations ........................................ 34
13. IPv6 Considerations ........................................ 34
14. Acknowledgments ............................................ 34
15. Normative References ....................................... 35
16. Informative References ..................................... 35
17. Authors' Addresses ......................................... 36
18. Full Copyright Statement ................................... 37
1. Introduction
The Ad hoc On-Demand Distance Vector (AODV) algorithm enables
dynamic, self-starting, multihop routing between participating mobile
nodes wishing to establish and maintain an ad hoc network. AODV
allows mobile nodes to obtain routes quickly for new destinations,
and does not require nodes to maintain routes to destinations that
are not in active communication. AODV allows mobile nodes to respond
to link breakages and changes in network topology in a timely manner.
The operation of AODV is loop-free, and by avoiding the Bellman-Ford
"counting to infinity" problem offers quick convergence when the ad
hoc network topology changes (typically, when a node moves in the
network). When links break, AODV causes the affected set of nodes to
be notified so that they are able to invalidate the routes using the
lost link.
Perkins, et. al. Experimental [Page 2]
RFC 3561 AODV Routing July 2003
One distinguishing feature of AODV is its use of a destination
sequence number for each route entry. The destination sequence
number is created by the destination to be included along with any
route information it sends to requesting nodes. Using destination
sequence numbers ensures loop freedom and is simple to program.
Given the choice between two routes to a destination, a requesting
node is required to select the one with the greatest sequence number.
2. Overview
Route Requests (RREQs), Route Replies (RREPs), and Route Errors
(RERRs) are the message types defined by AODV. These message types
are received via UDP, and normal IP header processing applies. So,
for instance, the requesting node is expected to use its IP address
as the Originator IP address for the messages. For broadcast
messages, the IP limited broadcast address (255.255.255.255) is used.
This means that such messages are not blindly forwarded. However,
AODV operation does require certain messages (e.g., RREQ) to be
disseminated widely, perhaps throughout the ad hoc network. The
range of dissemination of such RREQs is indicated by the TTL in the
IP header. Fragmentation is typically not required.
As long as the endpoints of a communication connection have valid
routes to each other, AODV does not play any role. When a route to a
new destination is needed, the node broadcasts a RREQ to find a route
to the destination. A route can be determined when the RREQ reaches
either the destination itself, or an intermediate node with a 'fresh
enough' route to the destination. A 'fresh enough' route is a valid
route entry for the destination whose associated sequence number is
at least as great as that contained in the RREQ. The route is made
available by unicasting a RREP back to the origination of the RREQ.
Each node receiving the request caches a route back to the originator
of the request, so that the RREP can be unicast from the destination
along a path to that originator, or likewise from any intermediate
node that is able to satisfy the request.
Nodes monitor the link status of next hops in active routes. When a
link break in an active route is detected, a RERR message is used to
notify ot