draft-ietf-manet-aodv-12.txt   draft-ietf-manet-aodv-13.txt 
Mobile Ad Hoc Networking Working Group Charles E. Perkins Mobile Ad Hoc Networking Working Group Charles E. Perkins
INTERNET DRAFT Nokia Research Center INTERNET DRAFT Nokia Research Center
4 November 2002 Elizabeth M. Belding-Royer 17 February 2003 Elizabeth M. Belding-Royer
University of California, Santa Barbara University of California, Santa Barbara
Samir R. Das Samir R. Das
University of Cincinnati University of Cincinnati
Ad hoc On-Demand Distance Vector (AODV) Routing Ad hoc On-Demand Distance Vector (AODV) Routing
draft-ietf-manet-aodv-12.txt draft-ietf-manet-aodv-13.txt
Status of This Memo Status of This Memo
This document is a submission by the Mobile Ad Hoc Networking Working This document is a submission by the Mobile Ad Hoc Networking Working
Group of the Internet Engineering Task Force (IETF). Comments should Group of the Internet Engineering Task Force (IETF). Comments should
be submitted to the manet@ietf.org mailing list. be submitted to the manet@ietf.org mailing list.
Distribution of this memo is unlimited. Distribution of this memo is unlimited.
This document is an Internet-Draft and is in full conformance with This document is an Internet-Draft and is in full conformance with
skipping to change at page 1, line 61 skipping to change at page 1, line 61
Status of This Memo i Status of This Memo i
Abstract i Abstract i
1. Introduction 1 1. Introduction 1
2. Overview 1 2. Overview 1
3. AODV Terminology 3 3. AODV Terminology 3
4. Message Formats 5 4. Applicability Statement 5
4.1. Route Request (RREQ) Message Format . . . . . . . . . . . 5
4.2. Route Reply (RREP) Message Format . . . . . . . . . . . . 6
4.3. Route Error (RERR) Message Format . . . . . . . . . . . . 8
4.4. Route Reply Acknowledgment (RREP-ACK) Message Format . . 9
5. AODV Operation 9 5. Message Formats 5
5.1. Maintaining Sequence Numbers . . . . . . . . . . . . . . 9 5.1. Route Request (RREQ) Message Format . . . . . . . . . . . 5
5.2. Route Table Entries and Precursor Lists . . . . . . . . . 11 5.2. Route Reply (RREP) Message Format . . . . . . . . . . . . 7
5.3. Generating Route Requests . . . . . . . . . . . . . . . . 12 5.3. Route Error (RERR) Message Format . . . . . . . . . . . . 8
5.4. Controlling Dissemination of Route Request Messages . . . 13 5.4. Route Reply Acknowledgment (RREP-ACK) Message Format . . 9
5.5. Processing and Forwarding Route Requests . . . . . . . . 14
5.6. Generating Route Replies . . . . . . . . . . . . . . . . 15
5.6.1. Route Reply Generation by the Destination . . . . 16
5.6.2. Route Reply Generation by an Intermediate Node . 16
5.6.3. Generating Gratuitous RREPs . . . . . . . . . . . 17
5.7. Receiving and Forwarding Route Replies . . . . . . . . . 17
5.8. Operation over Unidirectional Links . . . . . . . . . . . 19
5.9. Hello Messages . . . . . . . . . . . . . . . . . . . . . 19
5.10. Maintaining Local Connectivity . . . . . . . . . . . . . 20
5.11. Route Error Messages, Route Expiry and Route Deletion . . 21
5.12. Local Repair . . . . . . . . . . . . . . . . . . . . . . 23
5.13. Actions After Reboot . . . . . . . . . . . . . . . . . . 24
5.14. Interfaces . . . . . . . . . . . . . . . . . . . . . . . 25
6. AODV and Aggregated Networks 25 6. AODV Operation 9
6.1. Maintaining Sequence Numbers . . . . . . . . . . . . . . 10
6.2. Route Table Entries and Precursor Lists . . . . . . . . . 11
6.3. Generating Route Requests . . . . . . . . . . . . . . . . 12
6.4. Controlling Dissemination of Route Request Messages . . . 13
6.5. Processing and Forwarding Route Requests . . . . . . . . 14
6.6. Generating Route Replies . . . . . . . . . . . . . . . . 16
6.6.1. Route Reply Generation by the Destination . . . . 16
6.6.2. Route Reply Generation by an Intermediate Node . 17
6.6.3. Generating Gratuitous RREPs . . . . . . . . . . . 17
6.7. Receiving and Forwarding Route Replies . . . . . . . . . 18
6.8. Operation over Unidirectional Links . . . . . . . . . . . 19
6.9. Hello Messages . . . . . . . . . . . . . . . . . . . . . 20
6.10. Maintaining Local Connectivity . . . . . . . . . . . . . 21
6.11. Route Error (RERR) Messages, Route Expiry and Route
Deletion . . . . . . . . . . . . . . . . . . . . . . . 22
6.12. Local Repair . . . . . . . . . . . . . . . . . . . . . . 23
6.13. Actions After Reboot . . . . . . . . . . . . . . . . . . 25
6.14. Interfaces . . . . . . . . . . . . . . . . . . . . . . . 26
7. Using AODV with Other Networks 26 7. AODV and Aggregated Networks 26
8. Extensions 26 8. Using AODV with Other Networks 27
8.1. Hello Interval Extension Format . . . . . . . . . . . . . 27
9. Configuration Parameters 27 9. Extensions 28
9.1. Hello Interval Extension Format . . . . . . . . . . . . . 28
10. Security Considerations 29 10. Configuration Parameters 29
11. IPv6 Considerations 30 11. Security Considerations 31
12. Acknowledgments 30 12. IANA Considerations 32
A. Draft Modifications 32 13. IPv6 Considerations 32
14. Acknowledgments 32
A. Draft Modifications 34
1. Introduction 1. Introduction
The Ad hoc On-Demand Distance Vector (AODV) algorithm enables The Ad hoc On-Demand Distance Vector (AODV) algorithm enables
dynamic, self-starting, multihop routing between participating mobile dynamic, self-starting, multihop routing between participating mobile
nodes wishing to establish and maintain an ad hoc network. AODV nodes wishing to establish and maintain an ad hoc network. AODV
allows mobile nodes to obtain routes quickly for new destinations, allows mobile nodes to obtain routes quickly for new destinations,
and does not require nodes to maintain routes to destinations that and does not require nodes to maintain routes to destinations that
are not in active communication. AODV allows mobile nodes to respond are not in active communication. AODV allows mobile nodes to respond
to link breakages and changes in network topology in a timely manner. 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 The operation of AODV is loop-free, and by avoiding the Bellman-Ford
``counting to infinity'' problem offers quick convergence when the ``counting to infinity'' problem offers quick convergence when the
ad hoc network topology changes (typically, when a node moves in 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 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 be notified so that they are able to invalidate the routes using the
lost link. lost link.
One distinguishing feature of AODV is its use of a destination One distinguishing feature of AODV is its use of a destination
sequence number for each route entry. The destination sequence sequence number for each route entry. The destination sequence
number is created by the destination for any route information it number is created by the destination to be included along with any
sends to requesting nodes. Using destination sequence numbers route information it sends to requesting nodes. Using destination
ensures loop freedom and is simple to program. Given the choice sequence numbers ensures loop freedom and is simple to program.
between two routes to a destination, a requesting node always selects Given the choice between two routes to a destination, a requesting
the one with the greatest sequence number. node is required to select the one with the greatest sequence number.
2. Overview 2. Overview
Route Requests (RREQs), Route Replies (RREPs), and Route Errors Route Requests (RREQs), Route Replies (RREPs), and Route Errors
(RERRs) are the message types defined by AODV. These message types (RERRs) are the message types defined by AODV. These message types
are received via UDP, and normal IP header processing applies. are received via UDP, and normal IP header processing applies.
So, for instance, the requesting node is expected to use its IP So, for instance, the requesting node is expected to use its IP
address as the Originator IP address for the messages. For broadcast address as the Originator IP address for the messages. For broadcast
messages, the IP limited broadcast address (255.255.255.255) is used. messages, the IP limited broadcast address (255.255.255.255) is used.
This means that such messages are not blindly forwarded. However, This means that such messages are not blindly forwarded. However,
skipping to change at page 2, line 22 skipping to change at page 2, line 24
at least as great as that contained in the RREQ. The route is made 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. available by unicasting a RREP back to the origination of the RREQ.
Each node receiving the request caches a route back to the originator 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 of the request, so that the RREP can be unicast from the destination
along a path to that originator, or likewise from any intermediate along a path to that originator, or likewise from any intermediate
node that is able to satisfy the request. node that is able to satisfy the request.
Nodes monitor the link status of next hops in active routes. When a 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 link break in an active route is detected, a RERR message is used to
notify other nodes that the loss of that link has occurred. The RERR notify other nodes that the loss of that link has occurred. The RERR
message indicates those destinations which are now unreachable due to message indicates those destinations (possibly subnets) which are no
the loss of the link. In order to enable this reporting mechanism, longer reachable by way of the broken link. In order to enable this
each node keeps a ``precursor list'', containing the IP address for reporting mechanism, each node keeps a ``precursor list'', containing
each its neighbors that are likely to use it as a next hop towards the IP address for each its neighbors that are likely to use it as a
the destination that is now unreachable. The information in the next hop towards each destination. The information in the precursor
precursor lists is most easily acquired during the processing for lists is most easily acquired during the processing for generation
generation of a RREP message, which by definition has to be sent to a of a RREP message, which by definition has to be sent to a node in a
node in a precursor list (see section 5.6). precursor list (see section 6.6). If the RREP has a nonzero prefix
length, then the originator of the RREQ which solicited the RREP
information is included among the precursors for the subnet route
(not specifically for the particular destination).
A RREQ may also be received for a multicast IP address. In this A RREQ may also be received for a multicast IP address. In this
document, full processing for such messages is not specified. For document, full processing for such messages is not specified. For
example, the originator of such a RREQ for a multicast IP address example, the originator of such a RREQ for a multicast IP address
may have to follow special rules. However, it is important to may have to follow special rules. However, it is important to
enable correct multicast operation by intermediate nodes that are enable correct multicast operation by intermediate nodes that are
not enabled as originating or destination nodes for IP multicast not enabled as originating or destination nodes for IP multicast
addresses, and likewise are not equipped for any special multicast addresses, and likewise are not equipped for any special multicast
protocol processing. For such multicast-unaware nodes, processing protocol processing. For such multicast-unaware nodes, processing
for a multicast IP address as a destination IP address MUST be for a multicast IP address as a destination IP address MUST be
carried out in the same way as for any other destination IP address. carried out in the same way as for any other destination IP address.
AODV is a routing protocol, and it deals with route table AODV is a routing protocol, and it deals with route table
management. Route table information must be kept even management. Route table information must be kept even
for short-lived routes, such as are created to temporarily for short-lived routes, such as are created to temporarily
store reverse paths towards nodes originating RREQs. AODV store reverse paths towards nodes originating RREQs. AODV
uses the following fields with each route table entry: uses the following fields with each route table entry:
- Destination IP Address - Destination IP Address
- Destination Sequence Number - Destination Sequence Number
- Valid Destination Sequence Number - Valid Destination Sequence Number flag
- Interface -
- Other state and routing flags (e.g., valid, invalid, repairable,
being repaired)
- Network Interface
- Hop Count (number of hops needed to reach destination) - Hop Count (number of hops needed to reach destination)
- Next Hop - Next Hop
- List of Precursors (described in Section 5.2) - List of Precursors (described in Section 6.2)
- Lifetime (expiration or deletion time of the route) - Lifetime (expiration or deletion time of the route)
- Routing Flags
- State
Managing the sequence number is crucial to avoiding routing loops, Managing the sequence number is crucial to avoiding routing loops,
even when links break and a node is no longer reachable to supply even when links break and a node is no longer reachable to supply
its own information about its sequence number. A destination its own information about its sequence number. A destination
becomes unreachable when a link breaks or is deactivated. When these becomes unreachable when a link breaks or is deactivated. When these
conditions occur, the route is invalidated by operations involving conditions occur, the route is invalidated by operations involving
the sequence number and marking the route table entry state as the sequence number and marking the route table entry state as
invalid. See section 5.1 for details. invalid. See section 6.1 for details.
3. AODV Terminology 3. AODV Terminology
This protocol specification uses conventional meanings [2] for This protocol specification uses conventional meanings [1] for
capitalized words such as MUST, SHOULD, etc., to indicate requirement capitalized words such as MUST, SHOULD, etc., to indicate requirement
levels for various protocol features. This section defines other levels for various protocol features. This section defines other
terminology used with AODV that is not already defined in [3]. terminology used with AODV that is not already defined in [3].
active route active route
A route towards a destination that has a routing table entry A route towards a destination that has a routing table entry
that is marked as valid. Only active routes can be used to that is marked as valid. Only active routes can be used to
forward data packets. forward data packets.
skipping to change at page 3, line 49 skipping to change at page 3, line 50
Broadcasting means transmitting to the IP Limited Broadcast Broadcasting means transmitting to the IP Limited Broadcast
address, 255.255.255.255. A broadcast packet may not be address, 255.255.255.255. A broadcast packet may not be
blindly forwarded, but broadcasting is useful to enable blindly forwarded, but broadcasting is useful to enable
dissemination of AODV messages throughout the ad hoc network. dissemination of AODV messages throughout the ad hoc network.
destination destination
An IP address to which data packets are to be transmitted. An IP address to which data packets are to be transmitted.
Same as "destination node". A node knows it is the destination Same as "destination node". A node knows it is the destination
node for a data packet when its address appears in the node for a typical data packet when its address appears in the
appropriate field of the IP header. Routes for destination appropriate field of the IP header. Routes for destination
nodes are supplied by action of the AODV protocol, which nodes are supplied by action of the AODV protocol, which
carries the IP address of the destination node in route carries the IP address of the desired destination node in route
discovery messages. discovery messages.
forwarding node forwarding node
A node that agrees to forward packets destined for another A node that agrees to forward packets destined for another
node, by retransmitting them to a next hop that is closer to node, by retransmitting them to a next hop that is closer to
the unicast destination along a path that has been set up using the unicast destination along a path that has been set up using
routing control messages. routing control messages.
forward route forward route
A route set up to send data packets from a node originating a A route set up to send data packets from a node originating a
Route Discovery operation towards its desired destination. Route Discovery operation towards its desired destination.
invalid route invalid route
A route that has expired, denoted by a state of invalid in A route that has expired, denoted by a state of invalid in
the routing table. An invalid route is used to store the the routing table entry. An invalid route is used to store
previously valid route information for an extended period previously valid route information for an extended period of
of time. An invalid route may not be used to forward data time. An invalid route cannot be used to forward data packets,
packets. but it can provide information useful for route repairs, and
also for future RREQ messages.
originating node originating node
A node that initiates an AODV message to be processed and A node that initiates an AODV route discovery message to be
possibly retransmitted by other nodes in the ad hoc network. processed and possibly retransmitted by other nodes in the
For instance, the node initiating a Route Discovery process and ad hoc network. For instance, the node initiating a Route
broadcasting the RREQ message is called the originating node of Discovery process and broadcasting the RREQ message is called
the RREQ message. the originating node of the RREQ message.
reverse route reverse route
A route set up to forward a reply (RREP) packet back to the A route set up to forward a reply (RREP) packet back to the
originator from the destination or from an intermediate node originator from the destination or from an intermediate node
having a route to the destination. having a route to the destination.
sequence number sequence number
An increasing number maintained by each originating node. When A monotonically increasing number maintained by each
used in control messages it is used by other nodes to determine originating node. In AODV routing protocol messages, it
the freshness of the information contained from the originating is used by other nodes to determine the freshness of the
node. information contained from the originating node.
valid route valid route
See active route. See active route.
4. Message Formats 4. Applicability Statement
4.1. Route Request (RREQ) Message Format The AODV routing protocol is designed for mobile ad hoc networks
with populations of tens to thousands of mobile nodes. AODV can
handle low, moderate, and relatively high mobility rates, as well
as a variety of data traffic levels. AODV is designed for use in
networks where the nodes can all trust each other, either by use
of preconfigured keys, or because it is known that there are no
malicious intruder nodes. AODV has been designed to reduce the
dissemination of control traffic and eliminate overhead on data
traffic, in order to improve scalability and performance.
5. Message Formats
5.1. Route Request (RREQ) Message Format
0 1 2 3 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 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 |J|R|G|D|U| Reserved | Hop Count | | Type |J|R|G|D|U| Reserved | Hop Count |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RREQ ID | | RREQ ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Destination IP Address | | Destination IP Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
skipping to change at page 5, line 37 skipping to change at page 5, line 49
Type 1 Type 1
J Join flag; reserved for multicast. J Join flag; reserved for multicast.
R Repair flag; reserved for multicast. R Repair flag; reserved for multicast.
G Gratuitous RREP flag; indicates whether a G Gratuitous RREP flag; indicates whether a
gratuitous RREP should be unicast to the node gratuitous RREP should be unicast to the node
specified in the Destination IP Address field (see specified in the Destination IP Address field (see
sections 5.3, 5.6.3) sections 6.3, 6.6.3)
D Destination only flag; indicates only the D Destination only flag; indicates only the
destination may respond to this RREQ (see destination may respond to this RREQ (see
section 5.5). section 6.5).
U Unknown sequence number; indicates the destination U Unknown sequence number; indicates the destination
sequence number is unknown(see section 5.3). sequence number is unknown (see section 6.3).
Reserved Sent as 0; ignored on reception. Reserved Sent as 0; ignored on reception.
Hop Count The number of hops from the Originator IP Address Hop Count The number of hops from the Originator IP Address
to the node handling the request. to the node handling the request.
RREQ ID A sequence number uniquely identifying the RREQ ID A sequence number uniquely identifying the
particular RREQ when taken in conjunction with the particular RREQ when taken in conjunction with the
originating node's IP address. originating node's IP address.
Destination IP Address Destination IP Address
The IP address of the destination for which a route The IP address of the destination for which a route
is desired. is desired.
Destination Sequence Number Destination Sequence Number
The greatest sequence number received in the The latest sequence number received in the past
past by the originator for any route towards the by the originator for any route towards the
destination. destination.
Originator IP Address Originator IP Address
The IP address of the node which originated the The IP address of the node which originated the
Route Request. Route Request.
Originator Sequence Number Originator Sequence Number
The current sequence number to be used for The current sequence number to be used in the route
route entries pointing to (and generated by) the entry pointing towards the originator of the route
originator of the route request. request.
4.2. Route Reply (RREP) Message Format 5.2. Route Reply (RREP) Message Format
0 1 2 3 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 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| Reserved |Prefix Sz| Hop Count | | Type |R|A| Reserved |Prefix Sz| Hop Count |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Destination IP address | | Destination IP address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Destination Sequence Number | | Destination Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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| Lifetime | | Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The format of the Route Reply message is illustrated above, and The format of the Route Reply message is illustrated above, and
contains the following fields: contains the following fields:
Type 2 Type 2
R Repair flag; used for multicast. R Repair flag; used for multicast.
A Acknowledgment required; see sections 4.4 and 5.7. A Acknowledgment required; see sections 5.4 and 6.7.
Reserved Sent as 0; ignored on reception. Reserved Sent as 0; ignored on reception.
Prefix Size If nonzero, the 5-bit Prefix Size specifies that the Prefix Size If nonzero, the 5-bit Prefix Size specifies that the
indicated next hop may be used for any nodes with indicated next hop may be used for any nodes with
the same routing prefix (as defined by the Prefix the same routing prefix (as defined by the Prefix
Size) as the requested destination. Size) as the requested destination.
Hop Count The number of hops from the Originator IP Address Hop Count The number of hops from the Originator IP Address
to the Destination IP Address. For multicast route to the Destination IP Address. For multicast route
skipping to change at page 7, line 27 skipping to change at page 8, line 8
The destination sequence number associated to the The destination sequence number associated to the
route. route.
Originator IP Address Originator IP Address
The IP address of the node which originated the RREQ The IP address of the node which originated the RREQ
for which the route is supplied. for which the route is supplied.
Lifetime The time in milliseconds for which nodes receiving Lifetime The time in milliseconds for which nodes receiving
the RREP consider the route to be valid. the RREP consider the route to be valid.
Note that the Prefix Size allows a Subnet Leader to supply a route Note that the Prefix Size allows a subnet router to supply a route
for every host in the subnet defined by the routing prefix, which for every host in the subnet defined by the routing prefix, which
is determined by the IP address of the Subnet Leader and the Prefix is determined by the IP address of the subnet router and the Prefix
Size. In order to make use of this feature, the Subnet Leader has to Size. In order to make use of this feature, the subnet router has
guarantee reachability to all the hosts sharing the indicated subnet to guarantee reachability to all the hosts sharing the indicated
prefix. The Subnet Leader is also responsible for maintaining the subnet prefix. See section 7 for details. When the prefix size is
Destination Sequence Number for the whole subnet. See section 6 for nonzero, any routing information (and precursor data) MUST be kept
details. with respect to the subnet route, not the individual destination IP
address on that subnet.
The 'A' bit is used in cases where the link over which the RREP The 'A' bit is used when the link over which the RREP message is sent
message is sent may be unreliable or unidirectional. When the may be unreliable or unidirectional. When the RREP message contains
RREP message contains the 'A' bit set, the receiver of the RREP is the 'A' bit set, the receiver of the RREP is expected to return a
expected to return a RREP-ACK message. See section 5.8. RREP-ACK message. See section 6.8.
4.3. Route Error (RERR) Message Format 5.3. Route Error (RERR) Message Format
0 1 2 3 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 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 |N| Reserved | DestCount | | Type |N| Reserved | DestCount |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Unreachable Destination IP Address (1) | | Unreachable Destination IP Address (1) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Unreachable Destination Sequence Number (1) | | Unreachable Destination Sequence Number (1) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|
skipping to change at page 8, line 46 skipping to change at page 9, line 16
The IP address of the destination that has become The IP address of the destination that has become
unreachable due to a link break. unreachable due to a link break.
Unreachable Destination Sequence Number Unreachable Destination Sequence Number
The sequence number in the route table entry for The sequence number in the route table entry for
the destination listed in the previous Unreachable the destination listed in the previous Unreachable
Destination IP Address field. Destination IP Address field.
The RERR message is sent whenever a link break causes one or more The RERR message is sent whenever a link break causes one or more
destinations to become unreachable from some of the node's neighbors. destinations to become unreachable from some of the node's neighbors.
See section 5.2 for information about how to maintain the appropriate See section 6.2 for information about how to maintain the appropriate
records for this determination, and section 5.11 for specification records for this determination, and section 6.11 for specification
about how to create the list of destinations. about how to create the list of destinations.
4.4. Route Reply Acknowledgment (RREP-ACK) Message Format 5.4. Route Reply Acknowledgment (RREP-ACK) Message Format
The Route Reply Acknowledgment (RREP-ACK) message MUST be sent in The Route Reply Acknowledgment (RREP-ACK) message MUST be sent in
response to a RREP message with the 'A' bit set (see section 4.2. response to a RREP message with the 'A' bit set (see section 5.2).
This is typically done when there is danger of unidirectional This is typically done when there is danger of unidirectional
links preventing the completion of a Route Discovery cycle (see links preventing the completion of a Route Discovery cycle (see
section 5.8). section 6.8).
0 1 0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Reserved | | Type | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type 4 Type 4
Reserved Sent as 0; ignored on reception. Reserved Sent as 0; ignored on reception.
5. AODV Operation 6. AODV Operation
This section describes the scenarios under which nodes generate Route This section describes the scenarios under which nodes generate Route
Request (RREQ), Route Reply (RREP) and Route Error (RERR) messages Request (RREQ), Route Reply (RREP) and Route Error (RERR) messages
for unicast communication towards a destination, and how the message for unicast communication towards a destination, and how the message
data are handled. In order to process the messages correctly, data are handled. In order to process the messages correctly,
certain state information has to be maintained in the route table certain state information has to be maintained in the route table
entries for the destinations of interest. entries for the destinations of interest.
All AODV messages are sent to port 654 using UDP. All AODV messages are sent to port 654 using UDP.
5.1. Maintaining Sequence Numbers 6.1. Maintaining Sequence Numbers
Every route table entry at every node MUST include the latest Every route table entry at every node MUST include the latest
information available about the sequence number for the IP address of information available about the sequence number for the IP address of
the destination node for which the route table entry is maintained. the destination node for which the route table entry is maintained.
This sequence number is called the "destination sequence number". It This sequence number is called the "destination sequence number". It
is updated whenever a node receives new (i.e., not stale) information is updated whenever a node receives new (i.e., not stale) information
about the sequence number from RREQ, RREP, or RERR messages that about the sequence number from RREQ, RREP, or RERR messages that
may be received related to that destination. AODV depends on each may be received related to that destination. AODV depends on each
node in the network to own and maintain its destination sequence node in the network to own and maintain its destination sequence
number to guarantee the loop-freedom of all routes towards that number to guarantee the loop-freedom of all routes towards that
node. A destination node increments its own sequence number in two node. A destination node increments its own sequence number in two
circumstances: circumstances:
- Immediately before a node originates a route discovery, it MUST - Immediately before a node originates a route discovery, it MUST
increment its own sequence number. This prevents problems with increment its own sequence number. This prevents conflicts with
deleted reverse routes to the originator of a RREQ. previously established reverse routes towards the originator of a
RREQ.
- Immediately before a destination node originates a RREP in - Immediately before a destination node originates a RREP in
response to a RREQ, it MUST update its own sequence number to response to a RREQ, it MUST update its own sequence number to
the maximum of its current sequence number and the destination the maximum of its current sequence number and the destination
sequence number in the RREQ packet. sequence number in the RREQ packet.
When the destination increments its sequence number, it MUST do so When the destination increments its sequence number, it MUST do so
by treating the sequence number value as if it were an unsigned by treating the sequence number value as if it were an unsigned
number. To accomplish sequence number rollover, if the sequence number. To accomplish sequence number rollover, if the sequence
number has already been assigned to be the largest possible number number has already been assigned to be the largest possible number
representable as a 32-bit unsigned integer (i.e., 4294967295), then representable as a 32-bit unsigned integer (i.e., 4294967295), then
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related to that destination in the AODV message MUST be discarded, related to that destination in the AODV message MUST be discarded,
since that information is stale compared to the node's currently since that information is stale compared to the node's currently
stored information. stored information.
The only other circumstance in which a node may change the The only other circumstance in which a node may change the
destination sequence number in one of its route table entries is destination sequence number in one of its route table entries is
in response to a lost or expired link to the next hop towards that in response to a lost or expired link to the next hop towards that
destination. The node determines which destinations use a particular destination. The node determines which destinations use a particular
next hop by consulting its routing table. In this case, for each next hop by consulting its routing table. In this case, for each
destination that uses the next hop, the node increments the sequence destination that uses the next hop, the node increments the sequence
number and marks the route as invalid (see also sections 5.11, 5.12). number and marks the route as invalid (see also sections 6.11, 6.12).
Whenever any fresh enough (i.e., containing a sequence number at Whenever any fresh enough (i.e., containing a sequence number at
least equal to the recorded sequence number) routing information for least equal to the recorded sequence number) routing information for
an affected destination is received by a node that has marked that an affected destination is received by a node that has marked that
route table entry as invalid, the node SHOULD update its route table route table entry as invalid, the node SHOULD update its route table
information according to the information contained in the update. information according to the information contained in the update.
A node may change the sequence number in the routing table entry of a A node may change the sequence number in the routing table entry of a
destination only if: destination only if:
- it is itself the destination node, and offers a new route to - it is itself the destination node, and offers a new route to
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least equal to the recorded sequence number) routing information for least equal to the recorded sequence number) routing information for
an affected destination is received by a node that has marked that an affected destination is received by a node that has marked that
route table entry as invalid, the node SHOULD update its route table route table entry as invalid, the node SHOULD update its route table
information according to the information contained in the update. information according to the information contained in the update.
A node may change the sequence number in the routing table entry of a A node may change the sequence number in the routing table entry of a
destination only if: destination only if:
- it is itself the destination node, and offers a new route to - it is itself the destination node, and offers a new route to
itself, or itself, or
- it receives an AODV message with new information about the - it receives an AODV message with new information about the
sequence number for a destination node, or sequence number for a destination node, or
- the path towards the destination node expires or breaks. - the path towards the destination node expires or breaks.
5.2. Route Table Entries and Precursor Lists 6.2. Route Table Entries and Precursor Lists
When a node receives an AODV control packet from a neighbor, or When a node receives an AODV control packet from a neighbor, or
creates or updates a route for a particular destination, it checks creates or updates a route for a particular destination or subnet,
its route table for an entry for the destination. In the event it checks its route table for an entry for the destination. In the
that there is no corresponding entry for that destination, an entry event that there is no corresponding entry for that destination, an
is created. The sequence number is either determined from the entry is created. The sequence number is either determined from
information contained in the control packet, or else the valid the information contained in the control packet, or else the valid
sequence number field is set to false. The route is only updated if sequence number field is set to false. The route is only updated if
the new sequence number is either the new sequence number is either
(i) higher than the destination sequence number in the route (i) higher than the destination sequence number in the route
table, or table, or
(ii) the sequence numbers are equal, but the hop count (of (ii) the sequence numbers are equal, but the hop count (of
the new information) plus one, is smaller than the the new information) plus one, is smaller than the
existing hop count in the routing table, or existing hop count in the routing table, or
(iii) the sequence number is unknown. (iii) the sequence number is unknown.
The Lifetime field of the routing table entry is either The Lifetime field of the routing table entry is either
determined from the control packet, or it is initialized to determined from the control packet, or it is initialized to
ACTIVE_ROUTE_TIMEOUT. This route may now be used to send any queued ACTIVE_ROUTE_TIMEOUT. This route may now be used to send any queued
data packets and fulfills any outstanding route requests. data packets and fulfills any outstanding route requests.
Each time a route is used to forward a data packet, its Active Each time a route is used to forward a data packet, its Active
Route Lifetime field of the source, destination and the next hop Route Lifetime field of the source, destination and the next hop
on the path to the destination is updated to be no less than the on the path to the destination is updated to be no less than the
current time plus ACTIVE_ROUTE_TIMEOUT. Since the route between each current time plus ACTIVE_ROUTE_TIMEOUT. Since the route between
originator and destination pair are expected to be symmetric, the each originator and destination pair is expected to be symmetric,
Active Route Lifetime for the previous hop, along the reverse path the Active Route Lifetime for the previous hop, along the reverse
back to the IP source, is also updated to be no less than the current path back to the IP source, is also updated to be no less than the
time plus ACTIVE_ROUTE_TIMEOUT. current time plus ACTIVE_ROUTE_TIMEOUT. The lifetime for an Active
Route is updated each time the route is used regardless of whether
the destination is a single node or a subnet.
For each valid route maintained by a node as a routing table entry, For each valid route maintained by a node as a routing table entry,
the node also maintains a list of precursors that may be forwarding the node also maintains a list of precursors that may be forwarding
packets on this route. These precursors will receive notifications packets on this route. These precursors will receive notifications
from the node in the event of detection of the loss of the next hop from the node in the event of detection of the loss of the next hop
link. The list of precursors in a routing table entry contains those link. The list of precursors in a routing table entry contains those
neighboring nodes to which a route reply was generated or forwarded. neighboring nodes to which a route reply was generated or forwarded.
5.3. Generating Route Requests 6.3. Generating Route Requests
A node disseminates a RREQ when it determines that it needs a route A node disseminates a RREQ when it determines that it needs a route
to a destination and does not have one available. This can happen if to a destination and does not have one available. This can happen if
the destination is previously unknown to the node, or if a previously the destination is previously unknown to the node, or if a previously
valid route to the destination expires or is marked as invalid. The valid route to the destination expires or is marked as invalid. The
Destination Sequence Number field in the RREQ message is the last Destination Sequence Number field in the RREQ message is the last
known destination sequence number for this destination and is copied known destination sequence number for this destination and is copied
from the Destination Sequence Number field in the routing table. If from the Destination Sequence Number field in the routing table. If
no sequence number is known, the unknown sequence number flag MUST no sequence number is known, the unknown sequence number flag MUST
be set. The Originator Sequence Number in the RREQ message is the be set. The Originator Sequence Number in the RREQ message is the
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PATH_DISCOVERY_TIME. In this way, when the node receives the packet PATH_DISCOVERY_TIME. In this way, when the node receives the packet
again from its neighbors, it will not reprocess and re-forward the again from its neighbors, it will not reprocess and re-forward the
packet. packet.
An originating node often expects to have bidirectional An originating node often expects to have bidirectional
communications with a destination node. In such cases, it is communications with a destination node. In such cases, it is
not sufficient for the originating node to have a route to the not sufficient for the originating node to have a route to the
destination node; the destination must also have a route back to destination node; the destination must also have a route back to
the originating node. In order for this to happen as efficiently the originating node. In order for this to happen as efficiently
as possible, any generation of a RREP by an intermediate node (as as possible, any generation of a RREP by an intermediate node (as
in section 5.6) for delivery to the originating node SHOULD be in section 6.6) for delivery to the originating node SHOULD be
accompanied by some action that notifies the destination about a accompanied by some action that notifies the destination about a
route back to the originating node. The originating node selects route back to the originating node. The originating node selects
this mode of operation in the intermediate nodes by setting the `G' this mode of operation in the intermediate nodes by setting the `G'
flag. See section 5.6.3 for details about actions taken by the flag. See section 6.6.3 for details about actions taken by the
intermediate node in response to a RREQ with the `G' flag set. intermediate node in response to a RREQ with the `G' flag set.
A node SHOULD NOT generate more than RREQ_RATELIMIT RREQ messages A node SHOULD NOT originate more than RREQ_RATELIMIT RREQ messages
per second. After broadcasting a RREQ, a node waits for a RREP (or per second. After broadcasting a RREQ, a node waits for a RREP (or
other control message with current information regarding a route to other control message with current information regarding a route to
the appropriate destination). If a route is not received within the appropriate destination). If a route is not received within
NET_TRAVERSAL_TIME milliseconds, the node MAY try again to discover a NET_TRAVERSAL_TIME milliseconds, the node MAY try again to discover a
route by broadcasting another RREQ, up to a maximum of RREQ_RETRIES route by broadcasting another RREQ, up to a maximum of RREQ_RETRIES
times at the maximum TTL value. Each new attempt MUST increment and times at the maximum TTL value. Each new attempt MUST increment and
update the RREQ ID. For each attempt, the TTL field of the IP header update the RREQ ID. For each attempt, the TTL field of the IP header
is set according to the mechanism specified in section 5.4, in order is set according to the mechanism specified in section 6.4, in order
to enable control over how far the RREQ is disseminated for the each to enable control over how far the RREQ is disseminated for the each
retry. retry.
Data packets waiting for a route (i.e., waiting for a RREP after a Data packets waiting for a route (i.e., waiting for a RREP after a
RREQ has been sent) SHOULD be buffered. The buffering SHOULD be RREQ has been sent) SHOULD be buffered. The buffering SHOULD be
"first-in, first-out" (FIFO). If a route discovery has been attempted "first-in, first-out" (FIFO). If a route discovery has been attempted
RREQ_RETRIES times at the maximum TTL without receiving any RREP, all RREQ_RETRIES times at the maximum TTL without receiving any RREP, all
data packets destined for the corresponding destination SHOULD be data packets destined for the corresponding destination SHOULD be
dropped from the buffer and a Destination Unreachable message SHOULD dropped from the buffer and a Destination Unreachable message SHOULD
be delivered to the application. be delivered to the application.
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node sends a new RREQ. When calculating the time to wait for node sends a new RREQ. When calculating the time to wait for
the RREP after sending the second RREQ, the source node MUST use the RREP after sending the second RREQ, the source node MUST use
a binary exponential backoff. Hence, the waiting time for the a binary exponential backoff. Hence, the waiting time for the
RREP corresponding to the second RREQ is 2 * NET_TRAVERSAL_TIME RREP corresponding to the second RREQ is 2 * NET_TRAVERSAL_TIME
milliseconds. If a RREP is not receivied within this time period, milliseconds. If a RREP is not receivied within this time period,
another RREQ may be sent, up to RREQ_RETRIES additional attempts another RREQ may be sent, up to RREQ_RETRIES additional attempts
after the first RREQ. For each additional attempt, the waiting time after the first RREQ. For each additional attempt, the waiting time
for the RREP is multiplied by 2, so that the time conforms to a for the RREP is multiplied by 2, so that the time conforms to a
binary exponential backoff. binary exponential backoff.
5.4. Controlling Dissemination of Route Request Messages 6.4. Controlling Dissemination of Route Request Messages
To prevent unnecessary network-wide dissemination of RREQs, the To prevent unnecessary network-wide dissemination of RREQs, the
originating node SHOULD use an expanding ring search technique. originating node SHOULD use an expanding ring search technique.
In an expanding ring search, the originating node initially In an expanding ring search, the originating node initially
uses a TTL = TTL_START in the RREQ packet IP header and sets the uses a TTL = TTL_START in the RREQ packet IP header and sets the
timeout for receiving a RREP to RING_TRAVERSAL_TIME milliseconds. timeout for receiving a RREP to RING_TRAVERSAL_TIME milliseconds.
RING_TRAVERSAL_TIME is calculcated as described in section 9. The RING_TRAVERSAL_TIME is calculcated as described in section 10. The
TTL_VALUE used in calculating RING_TRAVERSAL_TIME is set equal to TTL_VALUE used in calculating RING_TRAVERSAL_TIME is set equal to
the value of the TTL field in the IP header. If the RREQ times out the value of the TTL field in the IP header. If the RREQ times out
without a corresponding RREP, the originator broadcasts the RREQ without a corresponding RREP, the originator broadcasts the RREQ
again with the TTL incremented by TTL_INCREMENT. This continues until again with the TTL incremented by TTL_INCREMENT. This continues until
the TTL set in the RREQ reaches TTL_THRESHOLD, beyond which a TTL = the TTL set in the RREQ reaches TTL_THRESHOLD, beyond which a TTL =
NET_DIAMETER is used for each attempt. Each time, the timeout for NET_DIAMETER is used for each attempt. Each time, the timeout for
receiving a RREP is RING_TRAVERSAL_TIME. When it is desired to have receiving a RREP is RING_TRAVERSAL_TIME. When it is desired to have
all retries traverse the entire ad hoc network, this can be achieved all retries traverse the entire ad hoc network, this can be achieved
by configuring TTL_START and TTL_INCREMENT both to be the same value by configuring TTL_START and TTL_INCREMENT both to be the same value
as NET_DIAMETER. as NET_DIAMETER.
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by configuring TTL_START and TTL_INCREMENT both to be the same value by configuring TTL_START and TTL_INCREMENT both to be the same value
as NET_DIAMETER. as NET_DIAMETER.
The Hop Count stored in an invalid routing table entry indicates The Hop Count stored in an invalid routing table entry indicates
the last known hop count to that destination in the routing table. the last known hop count to that destination in the routing table.
When a new route to the same destination is required at a later time When a new route to the same destination is required at a later time
(e.g., upon route loss), the TTL in the RREQ IP header is initially (e.g., upon route loss), the TTL in the RREQ IP header is initially
set to the Hop Count plus TTL_INCREMENT. Thereafter, following set to the Hop Count plus TTL_INCREMENT. Thereafter, following
each timeout the TTL is incremented by TTL_INCREMENT until TTL = each timeout the TTL is incremented by TTL_INCREMENT until TTL =
TTL_THRESHOLD is reached. Beyond this TTL = NET_DIAMETER is used. TTL_THRESHOLD is reached. Beyond this TTL = NET_DIAMETER is used.
Once TTL = NET_DIAMETER, the timeout for waiting for the RREP is set Once TTL = NET_DIAMETER, the timeout for waiting for the RREP is set
to NET_TRAVERSAL_TIME, as specified in section 5.3. to NET_TRAVERSAL_TIME, as specified in section 6.3.
An expired routing table entry SHOULD NOT be expunged before An expired routing table entry SHOULD NOT be expunged before
(current_time + DELETE_PERIOD) (see section 5.11). Otherwise, the (current_time + DELETE_PERIOD) (see section 6.11). Otherwise, the
soft state corresponding to the route (e.g., last known hop count) soft state corresponding to the route (e.g., last known hop count)
will be lost. Furthermore, a longer routing table entry expunge time will be lost. Furthermore, a longer routing table entry expunge time
MAY be configured. Any routing table entry waiting for a RREP SHOULD MAY be configured. Any routing table entry waiting for a RREP SHOULD
NOT be expunged before (current_time + 2 * NET_TRAVERSAL_TIME). NOT be expunged before (current_time + 2 * NET_TRAVERSAL_TIME).
5.5. Processing and Forwarding Route Requests 6.5. Processing and Forwarding Route Requests
When a node receives a RREQ, it first creates or updates a route to When a node receives a RREQ, it first creates or updates a route to
the previous hop without a valid sequence number (see section 5.2) the previous hop without a valid sequence number (see section 6.2)
then checks to determine whether it has received a RREQ with then checks to determine whether it has received a RREQ with
the same Originator IP Address and RREQ ID within at least the the same Originator IP Address and RREQ ID within at least the
last PATH_DISCOVERY_TIME. If such a RREQ has been received, the last PATH_DISCOVERY_TIME. If such a RREQ has been received, the
node silently discards the newly received RREQ. The rest of this node silently discards the newly received RREQ. The rest of this
subsection describes actions taken for RREQs that are not discarded. subsection describes actions taken for RREQs that are not discarded.
First, it first increments the hop count value in the RREQ by one, First, it first increments the hop count value in the RREQ by one,
to account for the new hop through the intermediate node. Then the to account for the new hop through the intermediate node. Then the
node creates or updates a reverse route to the Originator IP Address node searches for a reverse route to the Originator IP Address (see
(see section 5.2) using the Originator Sequence Number from the RREQ section 6.2), using longest-prefix matching. If need be, the route
in its routing table. This reverse route will be needed if the node is created, or updated using the Originator Sequence Number from the
receives a RREP back to the node that originated the RREQ (identified RREQ in its routing table. This reverse route will be needed if
by the Originator IP Address). When the reverse route is created or the node receives a RREP back to the node that originated the RREQ
updated, the following actions on the route are also carried out: (identified by the Originator IP Address). When the reverse route
is created or updated, the following actions on the route are also
carried out:
1. the Originator Sequence Number from the RREQ is copied to the 1. the Originator Sequence Number from the RREQ is compared to the
corresponding destination sequence number in the route table corresponding destination sequence number in the route table
entry and the valid sequence number field is set to true; entry and copied if greater than the existing value there
2. the next hop in the routing table becomes the node from which the 2. the valid sequence number field is set to true;
3. the next hop in the routing table becomes the node from which the
RREQ was received (it is obtained from the source IP address in RREQ was received (it is obtained from the source IP address in
the IP header and is often not equal to the Originator IP Address the IP header and is often not equal to the Originator IP Address
field in the RREQ message); field in the RREQ message);
3. the hop count is copied from the Hop Count in the RREQ message; 4. the hop count is copied from the Hop Count in the RREQ message;
Whenever a RREQ message is received, the Lifetime of the reverse Whenever a RREQ message is received, the Lifetime of the reverse
route entry for the Originator IP address is set to be the maximum of route entry for the Originator IP address is set to be the maximum of
(ExistingLifetime, MinimalLifetime), where (ExistingLifetime, MinimalLifetime), where
MinimalLifetime = (current time + 2*NET_TRAVERSAL_TIME - MinimalLifetime = (current time + 2*NET_TRAVERSAL_TIME -
2*HopCount*NODE_TRAVERSAL_TIME). 2*HopCount*NODE_TRAVERSAL_TIME).
The current node can now begin using the reverse route to forward The current node can use the reverse route to forward data packets in
data packets. the same way as for any other route in the routing table.
The node generates a RREP (as discussed further in section 5.6) if If a node does not generate a RREP (following the processing rules in
either: section 6.6), and if the incoming IP header has TTL larger than 1,
the node updates and broadcasts the RREQ to address 255.255.255.255
on each of its configured interfaces (see section 6.14). To update
the RREQ, the TTL or hop limit field in the outgoing IP header
is decreased by one, and the Hop Count field in the RREQ message
is incremented by one, to account for the new hop through the
intermediate node. Lastly, the Destination Sequence number for the
requested destination is set to the maximum of the corresponding
value received in the RREQ message, and the destination sequence
value currently maintained by the node for the requested destination.
However, the forwarding node MUST NOT modify its maintained value for
the destination sequence number, even if the value received in the
incoming RREQ is larger than the value currently maintained by the
forwarding node.
(i) it is itself the destination (see section 5.6.1), or Otherwise, if a node does generate a RREP, then the node discards the
RREQ. Notice that, if intermediate nodes reply to every transmission
of RREQs for a particular destination, it might turn out that the
destination does not receive any of the discovery messages. In
this situation, the destination does not learn of a route to the
originating node from the RREQ messages. This could cause the
destination to initiate a route discovery (for example, if the
originator is attempting to establish a TCP session). In order
that the destination learn of routes to the originating node, the
originating node SHOULD set the ``gratuitous RREP'' ('G') flag in the
RREQ if for any reason the destination is likely to need a route to
the originating node. If, in response to a RREQ with the 'G' flag
set, an intermediate node returns a RREP, it MUST also unicast a
gratuitous RREP to the destination node (see section 6.6.3).
6.6. Generating Route Replies
A node generates a RREP if either:
(i) it is itself the destination, or
(ii) it has an active route to the destination, the (ii) it has an active route to the destination, the
destination sequence number in the node's existing route destination sequence number in the node's existing route
table entry for the destination is valid and greater table entry for the destination is valid and greater
than or equal to the Destination Sequence Number of the than or equal to the Destination Sequence Number of the
RREQ (comparison using signed 32-bit arithmetic), and RREQ (comparison using signed 32-bit arithmetic), and
the ``destination only'' ('D') flag is NOT set. See the ``destination only'' ('D') flag is NOT set.
section 5.6.2 for further information about generating
the RREP in this case.
When either of these conditions is satisfied, the node does not
rebroadcast the RREQ.
Otherwise, if the incoming IP header has TTL larger than 1, the node
updates and broadcasts the RREQ to address 255.255.255.255 on all of
its configured interface(s) (see section 5.14). To update the RREQ,
the TTL or hop limit field in the outgoing IP header is decreased
by one, and the Hop Count field in the RREQ message is incremented
by one, to account for the new hop through the intermediate node.
Lastly, the Destination Sequence number for the requested destination
is set to the maximum of the corresponding value received in the RREQ
message, and the destination sequence value currently maintained by
the node for the requested destination. However, the forwarding node
MUST NOT modify its maintained value for the destination sequence
number, even if the value received in the incoming RREQ is larger
than the value currently maintained by the forwarding node.
5.6. Generating Route Replies
If a node receives a route request for a destination, and either When generating a RREP message, a node copies the Destination IP
has a fresh enough route to satisfy the request or is itself the Address and the Originator Sequence Number from the RREQ message
destination, the node generates a RREP message. This node copies into the corresponding fields in the RREP message. Processing is
the Destination IP Address and the Originator Sequence Number in slightly different, depending on whether the node is itself the
RREQ message into the corresponding fields in the RREP message. requested destination (see section 6.6.1), or instead if it is an
Processing is slightly different, depending on whether the node is intermediate node with an fresh enough route to the destination (see
itself the requested destination, or instead if it is an intermediate section 6.6.2).
node with an fresh enough route to the destination. These scenarios
are described in the sections below.
Once created, the RREP is unicast to the next hop toward the Once created, the RREP is unicast to the next hop toward the
originator of the RREQ, as indicated by the route table entry for originator of the RREQ, as indicated by the route table entry for
that originator. As the RREP is forwarded back towards the node that originator. As the RREP is forwarded back towards the node
which originated the RREQ message, the Hop Count field is incremented which originated the RREQ message, the Hop Count field is incremented
by one at each hop. Thus, when the RREP reaches the originator, the by one at each hop. Thus, when the RREP reaches the originator, the
Hop Count represents the distance, in hops, of the destination from Hop Count represents the distance, in hops, of the destination from
the originator. the originator.
5.6.1. Route Reply Generation by the Destination 6.6.1. Route Reply Generation by the Destination
If the generating node is the destination itself, it MUST increment If the generating node is the destination itself, it MUST increment
its own sequence number by one if the sequence number in the its own sequence number by one if the sequence number in the
RREQ packet is equal to that incremented value. Otherwise, the RREQ packet is equal to that incremented value. Otherwise, the
destination does not change its sequence number before generating destination does not change its sequence number before generating
the RREP message. The destination node places its (perhaps newly the RREP message. The destination node places its (perhaps newly
incremented) sequence number into the Destination Sequence Number incremented) sequence number into the Destination Sequence Number
field of the RREP, and enters the value zero in the Hop Count field field of the RREP, and enters the value zero in the Hop Count field
of the RREP. of the RREP.
The destination node copies the value MY_ROUTE_TIMEOUT (see The destination node copies the value MY_ROUTE_TIMEOUT (see
section 9) into the Lifetime field of the RREP. Each node MAY section 10) into the Lifetime field of the RREP. Each node MAY
reconfigure its value for MY_ROUTE_TIMEOUT, within mild constraints reconfigure its value for MY_ROUTE_TIMEOUT, within mild constraints
(see section 9). (see section 10).
5.6.2. Route Reply Generation by an Intermediate Node 6.6.2. Route Reply Generation by an Intermediate Node
If the node generating the RREP is not the destination node, but If the node generating the RREP is not the destination node, but
instead is an intermediate hop along the path from the originator instead is an intermediate hop along the path from the originator
to the destination, it copies its known sequence number for the to the destination, it copies its known sequence number for the
destination into the Destination Sequence Number field in the RREP destination into the Destination Sequence Number field in the RREP
message. message.
The intermediate node updates the forward route entry by placing the The intermediate node updates the forward route entry by placing the
last hop node (from which it received the RREQ, as indicated by the last hop node (from which it received the RREQ, as indicated by the
source IP address field in the IP header) into the precursor list for source IP address field in the IP header) into the precursor list for
skipping to change at page 17, line 5 skipping to change at page 17, line 31
the destination in the precursor list for the reverse route entry the destination in the precursor list for the reverse route entry
-- i.e., the entry for the Originator IP Address field of the RREQ -- i.e., the entry for the Originator IP Address field of the RREQ
message data. message data.
The intermediate node places its distance in hops from the The intermediate node places its distance in hops from the
destination (indicated by the hop count in the routing table) Count destination (indicated by the hop count in the routing table) Count
field in the RREP. The Lifetime field of the RREP is calculated by field in the RREP. The Lifetime field of the RREP is calculated by
subtracting the current time from the expiration time in its route subtracting the current time from the expiration time in its route
table entry. table entry.
5.6.3. Generating Gratuitous RREPs 6.6.3. Generating Gratuitous RREPs
After a node receives a RREQ and responds with a RREP, it discards After a node receives a RREQ and responds with a RREP, it discards
the RREQ. If intermediate nodes reply to every transmission of a the RREQ. If the RREQ has the 'G' flag set, and the intermediate
given RREQ, the destination does not receive any copies of it. In node returns a RREP to the originating node, it MUST also unicast a
this situation, the destination does not learn of a route to the gratuitous RREP to the destination node. The gratuitous RREP that is
originating node. This could cause the destination to initiate a to be sent to the desired destination contains the following values
route discovery (for example, if the originator is attempting to in the RREP message fields:
establish a TCP session). In order that the destination learn of
routes to the originating node, the originating node SHOULD set
the ``gratuitous RREP'' ('G') flag in the RREQ if for any reason
the destination is likely to need a route to the originating node.
If, in response to a RREQ with the 'G' flag set, an intermediate
node returns a RREP, it MUST also unicast a gratuitous RREP to the
destination node.
The RREP that is sent to the originator of the RREQ is the same
as before. The gratuitous RREP that is to be sent to the desired
destination contains the following values in the RREP message fields:
Hop Count The Hop Count as indicated in the node's route table Hop Count The Hop Count as indicated in the node's route table
entry for the originator entry for the originator
Destination IP Address Destination IP Address
The IP address of the node that originated the RREQ The IP address of the node that originated the RREQ
Destination Sequence Number Destination Sequence Number
The Originator Sequence Number from the RREQ The Originator Sequence Number from the RREQ
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entry for the originator entry for the originator
Destination IP Address Destination IP Address
The IP address of the node that originated the RREQ The IP address of the node that originated the RREQ
Destination Sequence Number Destination Sequence Number
The Originator Sequence Number from the RREQ The Originator Sequence Number from the RREQ
Originator IP Address Originator IP Address
The IP address of the Destination node in the RREQ The IP address of the Destination node in the RREQ
Lifetime The remaining lifetime of the route towards the Lifetime The remaining lifetime of the route towards the
originator of the RREQ, as known by the intermediate originator of the RREQ, as known by the intermediate
node. node.
The gratuitous RREP is then sent to the next hop along the path to The gratuitous RREP is then sent to the next hop along the path to
the destination node, just as if the destination node had already the destination node, just as if the destination node had already
issued a RREQ for the originating node and this RREP was produced in issued a RREQ for the originating node and this RREP was produced
response to that (fictitious) RREQ. in response to that (fictitious) RREQ. The RREP that is sent to the
originator of the RREQ is the same whether or not the 'G' bit is set.
5.7. Receiving and Forwarding Route Replies 6.7. Receiving and Forwarding Route Replies
When a node receives a RREP message, it first creates or updates When a node receives a RREP message, it searches (using
a route to the previous hop without a valid sequence number (see longest-prefix matching) for a route to the previous hop. If needed,
section 5.2) then increments the hop count value in the RREP by one, a route is created for the previous hop, but without a valid sequence
to account for the new hop through the intermediate node. Call this number (see section 6.2). Next, the node then increments the hop
incremented value the "New Hop Count". Then the forward route for count value in the RREP by one, to account for the new hop through
this destination is created if it does not already exist. Otherwise, the intermediate node. Call this incremented value the "New Hop
the node compares the Destination Sequence Number in the message with Count". Then the forward route for this destination is created if it
its own stored destination sequence number for the Destination IP does not already exist. Otherwise, the node compares the Destination
Address in the RREP message. Upon comparison, the existing entry is Sequence Number in the message with its own stored destination
updated only if either sequence number for the Destination IP Address in the RREP message.
Upon comparison, the existing entry is updated only in the following
circumstances:
(i) the sequence number in the routing table is invalid in (i) the sequence number in the routing table is marked as
route table entry. invalid in route table entry.
(ii) the Destination Sequence Number in the RREP is greater (ii) the Destination Sequence Number in the RREP is greater
than the node's copy of the destination sequence number than the node's copy of the destination sequence number
and the known value is valid, or and the known value is valid, or
(iii) the sequence numbers are the same, but the route is no (iii) the sequence numbers are the same, but the route is is
longer active, or marked as inactive, or
(iv) the sequence numbers are the same, and the New Hop Count (iv) the sequence numbers are the same, and the New Hop Count
is smaller than the hop count in route table entry. is smaller than the hop count in route table entry.
If either the route table entry to the destination is created or If the route table entry to the destination is created or updated,
updated, the next hop in the route entry is assigned to be the node then the following actions occur:
from which the RREP is received, which is indicated by the source IP
address field in the IP header; the hop count is the New Hop Count; - the route is marked as active,
the expiry time is the current time plus the Lifetime in the RREP
message; and the destination sequence number is the Destination - the destination sequence number is marked as valid,
Sequence Number in the RREP message. The current node can now begin
using this route to forward data packets to the destination. - the next hop in the route entry is assigned to be the node
from which the RREP is received, which is indicated by the
source IP address field in the IP header,
- the hop count is set to the value of the New Hop Count,
- the expiry time is set to the current time plus the value of
the Lifetime in the RREP message,
- and the destination sequence number is the Destination
Sequence Number in the RREP message.
The current node can subsequently use this route to forward data
packets to the destination.
If the current node is not the node indicated by the Originator IP If the current node is not the node indicated by the Originator IP
Address in the RREP message AND a forward route has been created or Address in the RREP message AND a forward route has been created or
updated as described above, the node consults its route table entry updated as described above, the node consults its route table entry
for the originating node to determine the next hop for the RREP for the originating node to determine the next hop for the RREP
packet, and then forwards the RREP towards the originator using the packet, and then forwards the RREP towards the originator using the
information in that route table entry. If a node forwards a RREP information in that route table entry. If a node forwards a RREP
over a link that is likely to have errors or be unidirectional, the over a link that is likely to have errors or be unidirectional, the
node SHOULD set the `A' flag to require that the recipient of the node SHOULD set the `A' flag to require that the recipient of the
RREP acknowledge receipt of the RREP by sending a RREP-ACK message RREP acknowledge receipt of the RREP by sending a RREP-ACK message
back (see section 5.8). back (see section 6.8).
When any node transmits a RREP, the precursor list for the When any node transmits a RREP, the precursor list for the
corresponding destination node is updated by adding to it the corresponding destination node is updated by adding to it the
next hop node to which the RREP is forwarded. Also, at each next hop node to which the RREP is forwarded. Also, at each
node the (reverse) route used to forward a RREP has its lifetime node the (reverse) route used to forward a RREP has its lifetime
changed to be the maximum of (existing-lifetime, (current time + changed to be the maximum of (existing-lifetime, (current time +
ACTIVE_ROUTE_TIMEOUT)). Finally, the precursor list for the next hop ACTIVE_ROUTE_TIMEOUT)). Finally, the precursor list for the next hop
towards the destination is updated to contain the next hop towards towards the destination is updated to contain the next hop towards
the source. the source.
5.8. Operation over Unidirectional Links 6.8. Operation over Unidirectional Links
It is possible that a RREP transmission may fail, especially if the It is possible that a RREP transmission may fail, especially if the
RREQ transmission triggering the RREP occurs over a unidirectional RREQ transmission triggering the RREP occurs over a unidirectional
link. If no other RREP generated from the same route discovery link. If no other RREP generated from the same route discovery
attempt reaches the node which originated the RREQ message, the attempt reaches the node which originated the RREQ message, the
originator will reattempt route discovery after a timeout (see originator will reattempt route discovery after a timeout (see
section 5.3). However, the same scenario might well be repeated, and section 6.3). However, the same scenario might well be repeated
no route would be discovered even after repeated retries. Unless without any improvement, and no route would be discovered even after
corrective action is taken, this can happen even when bidirectional repeated retries. Unless corrective action is taken, this can happen
routes between originator and destination do exist. Link layers even when bidirectional routes between originator and destination
using broadcast transmissions for the RREQ will not be able to detect do exist. Link layers using broadcast transmissions for the RREQ
the presence of such unidirectional links. In AODV, any node acts on will not be able to detect the presence of such unidirectional links.
only the first RREQ with the same RREQ ID and ignores any subsequent In AODV, any node acts on only the first RREQ with the same RREQ ID
RREQs. Suppose, for example, that the first RREQ arrives along a and ignores any subsequent RREQs. Suppose, for example, that the
path that has one or more unidirectional link(s). A subsequent RREQ first RREQ arrives along a path that has one or more unidirectional
may arrive via a bidirectional path (assuming such paths exist), but link(s). A subsequent RREQ may arrive via a bidirectional path
it will be ignored. (assuming such paths exist), but it will be ignored.
To prevent this problem, when a node detects that its transmission of To prevent this problem, when a node detects that its transmission of
a RREP message has failed, it remembers the next-hop of the failed a RREP message has failed, it remembers the next-hop of the failed
RREP in a ``blacklist'' set. Such failures can be detected via RREP in a ``blacklist'' set. Such failures can be detected via
the absence of a link-layer or network-layer acknowledgment (e.g., the absence of a link-layer or network-layer acknowledgment (e.g.,
RREP-ACK). A node ignores all RREQs received from any node in its RREP-ACK). A node ignores all RREQs received from any node in its
blacklist set. Nodes are removed from the blacklist set after a blacklist set. Nodes are removed from the blacklist set after a
BLACKLIST_TIMEOUT period (see section 9). This period should be set BLACKLIST_TIMEOUT period (see section 10). This period should be set
to the upper bound of the time it takes to perform the allowed number to the upper bound of the time it takes to perform the allowed number
of route request retry attempts as described in section 5.3. of route request retry attempts as described in section 6.3.
Note that the RREP-ACK packet does not contain any information about Note that the RREP-ACK packet does not contain any information about
which RREP it is acknowledging. The time at which the RREP-ACK is which RREP it is acknowledging. The time at which the RREP-ACK
received will likely come just after the time when the RREP was sent is received will likely come just after the time when the RREP
with the 'A' bit. This information is expected to be sufficient was sent with the 'A' bit. This information is expected to be
to provide assurance to the sender of the RREP that the link is sufficient to provide assurance to the sender of the RREP that the
currently bidirectional. However, that assurance cannot be always link is currently bidirectional, without any real dependence on the
expected to remain permanently. particular RREP message being acknowledged. However, that assurance
typically cannot be expected to remain in force permanently.
5.9. Hello Messages 6.9. Hello Messages
A node MAY offer connectivity information by broadcasting local Hello A node MAY offer connectivity information by broadcasting local Hello
messages. A node SHOULD only use hello messages if it is part of an messages. A node SHOULD only use hello messages if it is part of an
active route. Every HELLO_INTERVAL milliseconds, the node checks active route. Every HELLO_INTERVAL milliseconds, the node checks
whether it has sent a broadcast (e.g., a RREQ or an appropriate layer whether it has sent a broadcast (e.g., a RREQ or an appropriate layer
2 message) within the last HELLO_INTERVAL. If it has not, it MAY 2 message) within the last HELLO_INTERVAL. If it has not, it MAY
broadcast a RREP with TTL = 1, called a Hello message, with the RREP broadcast a RREP with TTL = 1, called a Hello message, with the RREP
message fields set as follows: message fields set as follows:
Destination IP Address Destination IP Address
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Hop Count 0 Hop Count 0
Lifetime ALLOWED_HELLO_LOSS * HELLO_INTERVAL Lifetime ALLOWED_HELLO_LOSS * HELLO_INTERVAL
A node MAY determine connectivity by listening for packets from its A node MAY determine connectivity by listening for packets from its
set of neighbors. If, within the past DELETE_PERIOD, it has received set of neighbors. If, within the past DELETE_PERIOD, it has received
a Hello message from a neighbor, and then for that neighbor does a Hello message from a neighbor, and then for that neighbor does
not receive any packets (Hello messages or otherwise) for more than not receive any packets (Hello messages or otherwise) for more than
ALLOWED_HELLO_LOSS * HELLO_INTERVAL milliseconds, the node SHOULD ALLOWED_HELLO_LOSS * HELLO_INTERVAL milliseconds, the node SHOULD
assume that the link to this neighbor is currently lost. When this assume that the link to this neighbor is currently lost. When this
happens, the node SHOULD proceed as in Section 5.11. happens, the node SHOULD proceed as in Section 6.11.
Whenever a node receives a Hello message from a neighbor, the Whenever a node receives a Hello message from a neighbor, the
node SHOULD make sure that it has an active route to the neighbor, node SHOULD make sure that it has an active route to the neighbor,
and create one if necessary. If a route already exists, then the and create one if necessary. If a route already exists, then the
Lifetime for the route should be increased, if necessary, to be at Lifetime for the route should be increased, if necessary, to be at
least ALLOWED_HELLO_LOSS * HELLO_INTERVAL. The route to the neighbor, least ALLOWED_HELLO_LOSS * HELLO_INTERVAL. The route to the neighbor,
if it exists, MUST subsequently contain the latest Destination if it exists, MUST subsequently contain the latest Destination
Sequence Number from the Hello message. The current node can now Sequence Number from the Hello message. The current node can now
begin using this route to forward data packets. Routes that are begin using this route to forward data packets. Routes that are
created by hello messages and not used by any other active routes created by hello messages and not used by any other active routes
will have empty precursor lists and would not trigger a RERR message will have empty precursor lists and would not trigger a RERR message
when the neighbor moves away and a neighbor timeout occurs. if the neighbor moves away and a neighbor timeout occurs.
Also, whenever a node receives any control packet it has the same
meaning as the reception of an explicit Hello message, in that it
signifies an active connection to the node indicated by the Source IP
Address of the IP header of the control message packet.
5.10. Maintaining Local Connectivity 6.10. Maintaining Local Connectivity
Each forwarding node SHOULD keep track of its continued connectivity Each forwarding node SHOULD keep track of its continued connectivity
to its active next hops (i.e., which next hops or precursors have to its active next hops (i.e., which next hops or precursors have
forwarded packets to or from the forwarding node during the last forwarded packets to or from the forwarding node during the last
ACTIVE_ROUTE_TIMEOUT), as well as neighbors that have transmitted ACTIVE_ROUTE_TIMEOUT), as well as neighbors that have transmitted
Hello messages during the last (ALLOWED_HELLO_LOSS * HELLO_INTERVAL). Hello messages during the last (ALLOWED_HELLO_LOSS * HELLO_INTERVAL).
A node can maintain accurate information about its continued A node can maintain accurate information about its continued
connectivity to these active next hops, using one or more of the connectivity to these active next hops, using one or more of the
available link or network layer mechanisms, as described below. available link or network layer mechanisms, as described below.
- Any suitable link layer notification, such as those provided by - Any suitable link layer notification, such as those provided by
IEEE 802.11, can be used to determine connectivity, each time IEEE 802.11, can be used to determine connectivity, each time
a packet is transmitted to an active next hop. For example, a packet is transmitted to an active next hop. For example,
absence of a link layer ACK or failure to get a CTS after sending absence of a link layer ACK or failure to get a CTS after sending
RTS, even after the maximum number of retransmission attempts, RTS, even after the maximum number of retransmission attempts,
indicates loss of the link to this active next hop. indicates loss of the link to this active next hop.
- If possible, passive acknowledgment SHOULD be used when the - If layer-2 notification is not available, passive acknowledgment
next hop is expected to forward the packet, by listening to the SHOULD be used when the next hop is expected to forward the
channel for a transmission attempt made by the next hop. If packet, by listening to the channel for a transmission attempt
transmission is not detected within NEXT_HOP_WAIT milliseconds or made by the next hop. If transmission is not detected within
the next hop is the destination (and thus is never supposed to NEXT_HOP_WAIT milliseconds or the next hop is the destination
transmit the packet) one of the following methods should be used (and thus is not supposed to forward the packet) one of the
to determine connectivity. following methods SHOULD be used to determine connectivity:
* Receiving any packet (including a Hello message) from the * Receiving any packet (including a Hello message) from the
next hop. next hop.
* A RREQ unicast to the next hop, asking for a route to the * A RREQ unicast to the next hop, asking for a route to the
next hop. next hop.
* An ICMP Echo Request message unicast to the next hop. * An ICMP Echo Request message unicast to the next hop.
If a link to the next hop cannot be detected by any of these methods, If a link to the next hop cannot be detected by any of these methods,
the forwarding node SHOULD assume that the link is lost, and take the forwarding node SHOULD assume that the link is lost, and take
corrective action by following the methods specified in Section 5.11. corrective action by following the methods specified in Section 6.11.
5.11. Route Error Messages, Route Expiry and Route Deletion 6.11. Route Error (RERR) Messages, Route Expiry and Route Deletion
Generally, route error and link breakage processing requires the
following steps:
- Invalidating existing routes
- Listing affected destinations
- Determining which, if any, neighbors may be affected
- Delivering an appropriate RERR to such neighbors
A Route Error (RERR) message MAY be either broadcast (if there A Route Error (RERR) message MAY be either broadcast (if there
are many precursors), unicast (if there is only 1 precursor), are many precursors), unicast (if there is only 1 precursor),
or iteratively unicast to all precursors (if broadcast is or iteratively unicast to all precursors (if broadcast is
inappropriate). Even when the RERR message is iteratively unicast inappropriate). Even when the RERR message is iteratively unicast
to several precursors, it is considered to be a single control to several precursors, it is considered to be a single control
message for the purposes of the description in the text that follows. message for the purposes of the description in the text that follows.
With that understanding, a node SHOULD NOT generate more than With that understanding, a node SHOULD NOT generate more than
RERR_RATELIMIT RERR messages per second. RERR_RATELIMIT RERR messages per second.
A node initiates processing for a RERR message in three situations: A node initiates processing for a RERR message in three situations:
(i) if it detects a link break for the next hop of an active (i) if it detects a link break for the next hop of an active
route in its routing table while transmitting data, or route in its routing table while transmitting data (and
route repair, if attempted, was unsuccessful), or
(ii) if it gets a data packet destined to a node for which it (ii) if it gets a data packet destined to a node for which it
does not have an active route and is not repairing (if does not have an active route and is not repairing (if
using local repair), or using local repair), or
(iii) if it receives a RERR from a neighbor for one or more (iii) if it receives a RERR from a neighbor for one or more
active routes. active routes.
For case (i), the node first makes a list of unreachable destinations For case (i), the node first makes a list of unreachable destinations
consisting of the unreachable neighbor and any additional consisting of the unreachable neighbor and any additional
destinations in the local routing table that use the unreachable destinations (or subnets, see section 7) in the local routing
neighbor as the next hop. For case (ii), there is only one table that use the unreachable neighbor as the next hop. In this
unreachable destination, which is the destination of the data packet case, if a subnet route is found to be newly unreachable, an IP
that cannot be delivered. For case (iii), the list should consist of destination address for the subnet is constructed by appending
those destinations in the RERR for which there exists a corresponding zeroes to the subnet prefix as shown in the route table entry. This
entry in the local routing table that has the transmitter of the is unambiguous, since the precursor is known to have route table
received RERR as the next hop. information with a compatible prefix length for that subnet.
For case (ii), there is only one unreachable destination, which is
the destination of the data packet that cannot be delivered. For
case (iii), the list should consist of those destinations in the RERR
for which there exists a corresponding entry in the local routing
table that has the transmitter of the received RERR as the next hop.
Some of the unreachable destinations in the list could be used by Some of the unreachable destinations in the list could be used by
neighboring nodes, and it may therefore be necessary to send a (new) neighboring nodes, and it may therefore be necessary to send a (new)
RERR. The RERR should contain those destinations that are part of RERR. The RERR should contain those destinations that are part of
the created list of unreachable destinations and have a non-empty the created list of unreachable destinations and have a non-empty
precursor list. precursor list.
The neighboring node(s) that should receive the RERR are all those The neighboring node(s) that should receive the RERR are all those
that belong to a precursor list of at least one of the unreachable that belong to a precursor list of at least one of the unreachable
destination(s) in the newly created RERR. In case there is only destination(s) in the newly created RERR. In case there is only one
one unique neighbor that needs to receive the RERR, the RERR unique neighbor that needs to receive the RERR, the RERR SHOULD be
SHOULD be unicast toward that destination. Otherwise the RERR is unicast toward that neighbor. Otherwise the RERR is typically sent
typically sent to the local broadcast address (Destination IP == to the local broadcast address (Destination IP == 255.255.255.255,
255.255.255.255, TTL == 1) with the unreachable destinations, and TTL == 1) with the unreachable destinations, and their corresponding
their corresponding destination sequence numbers, included in the destination sequence numbers, included in the packet. The DestCount
packet. The DestCount field of the RERR packet indicates the number field of the RERR packet indicates the number of unreachable
of unreachable destinations included in the packet. destinations included in the packet.
Just before transmitting the RERR, certain updates are made on the Just before transmitting the RERR, certain updates are made on the
routing table that may affect the destination sequence numbers for routing table that may affect the destination sequence numbers for
the unreachable destinations. For each one of these destinations, the unreachable destinations. For each one of these destinations,
the corresponding routing table entry is updated as follows: the corresponding routing table entry is updated as follows:
1. The destination sequence number of this routing entry, if it 1. The destination sequence number of this routing entry, if it
exists and is valid, is incremented for cases (i) and (ii) above, exists and is valid, is incremented for cases (i) and (ii) above,
and copied from the incoming RERR in case (iii) above. and copied from the incoming RERR in case (iii) above.
2. The entry is invalidated by marking the route entry as invalid 2. The entry is invalidated by marking the route entry as invalid
3. The Lifetime field is updated to current time plus DELETE_PERIOD. 3. The Lifetime field is updated to current time plus DELETE_PERIOD.
Before this time, the entry SHOULD NOT be deleted. Before this time, the entry SHOULD NOT be deleted.
Note that the Lifetime field in the routing table plays dual role Note that the Lifetime field in the routing table plays dual role
-- for an active route it is the expiry time, and for an invalid -- for an active route it is the expiry time, and for an invalid
route it is the deletion time. If a data packet is received for an route it is the deletion time. If a data packet is received for an
invalid route, the Lifetime field is updated to current time plus invalid route, the Lifetime field is updated to current time plus
DELETE_PERIOD. The determination of DELETE_PERIOD is discussed in DELETE_PERIOD. The determination of DELETE_PERIOD is discussed in
Section 9. Section 10.
5.12. Local Repair 6.12. Local Repair
When a link break in an active route occurs, the node upstream of When a link break in an active route occurs, the node upstream of
that break MAY choose to repair the link locally if the destination that break MAY choose to repair the link locally if the destination
was no farther than MAX_REPAIR_TTL hops away. To repair the link was no farther than MAX_REPAIR_TTL hops away. To repair the link
break, the node increments the sequence number for the destination break, the node increments the sequence number for the destination
and then broadcasts a RREQ for that destination. The TTL of the RREQ and then broadcasts a RREQ for that destination. The TTL of the RREQ
should initially be set to the following value: should initially be set to the following value:
max(MIN_REPAIR_TTL, 0.5 * #hops) + LOCAL_ADD_TTL, max(MIN_REPAIR_TTL, 0.5 * #hops) + LOCAL_ADD_TTL,
where #hops is the number of hops to the sender (originator) of the where #hops is the number of hops to the sender (originator) of the
currently undeliverable packet. Thus, local repair attempts will currently undeliverable packet. Thus, local repair attempts will
often be invisible to the originating node, and will always have TTL often be invisible to the originating node, and will always have TTL
>= MIN_REPAIR_TTL + LOCAL_ADD_TTL. The node initiating the repair >= MIN_REPAIR_TTL + LOCAL_ADD_TTL. The node initiating the repair
then waits the discovery period to receive RREPs in response to the then waits the discovery period to receive RREPs in response to the
RREQ. During local repair data packets SHOULD be buffered. If, at RREQ. During local repair data packets SHOULD be buffered. If, at
the end of the discovery period, it has not received a RREP (or other the end of the discovery period, the reparing node has not received
control message creating or updating the route) for that destination, a RREP (or other control message creating or updating the route)
it proceeds as described in Section 5.11 by transmitting a RERR for that destination, it proceeds as described in Section 6.11 by
message for that destination. transmitting a RERR message for that destination.
On the other hand, if the node receives one or more RREPs (or On the other hand, if the node receives one or more RREPs (or
other control message creating or updating the route to the desired other control message creating or updating the route to the desired
destination) during the discovery period, it first compares the hop destination) during the discovery period, it first compares the hop
count of the new route with the value in the hop count field of the count of the new route with the value in the hop count field of the
invalid route table entry for that destination. If the hop count of invalid route table entry for that destination. If the hop count of
the newly determined route to the destination is greater than the the newly determined route to the destination is greater than the
hop count of the previously known route the node SHOULD issue a RERR hop count of the previously known route the node SHOULD issue a RERR
message for the destination, with the 'N' bit set. Then it proceeds message for the destination, with the 'N' bit set. Then it proceeds
as described in Section 5.7, updating its route table entry for that as described in Section 6.7, updating its route table entry for that
destination. destination.
A node that receives a RERR message with the 'N' flag set MUST NOT A node that receives a RERR message with the 'N' flag set MUST NOT
delete the route to that destination. The only action taken should delete the route to that destination. The only action taken should
be the retransmission of the message, if the RERR arrived from the be the retransmission of the message, if the RERR arrived from the
next hop along that route, and if there are one or more precursor next hop along that route, and if there are one or more precursor
nodes for that route to the destination. When the originating node nodes for that route to the destination. When the originating node
receives a RERR message with the 'N' flag set, if this message receives a RERR message with the 'N' flag set, if this message
came from its next hop along its route to the destination then came from its next hop along its route to the destination then
the originating node MAY choose to reinitiate route discovery, as the originating node MAY choose to reinitiate route discovery, as
described in Section 5.3. described in Section 6.3.
Local repair of link breaks in routes sometimes results in increased Local repair of link breaks in routes sometimes results in increased
path lengths to those destinations. Repairing the link locally is path lengths to those destinations. Repairing the link locally is
likely to increase the number of data packets that are able to be likely to increase the number of data packets that are able to be
delivered to the destinations, since data packets will not be dropped delivered to the destinations, since data packets will not be dropped
as the RERR travels to the originating node. Sending a RERR to the as the RERR travels to the originating node. Sending a RERR to the
originating node after locally repairing the link break may allow the originating node after locally repairing the link break may allow the
originator to find a fresh route to the destination that is better, originator to find a fresh route to the destination that is better,
based on current node positions. However, it does not require the based on current node positions. However, it does not require the
originating node to rebuild the route, as the originator may be done, originating node to rebuild the route, as the originator may be done,
skipping to change at page 24, line 35 skipping to change at page 25, line 31
of the link, incoming data packets for those routes will not be of the link, incoming data packets for those routes will not be
subject to the delay of repairing the route and can be immediately subject to the delay of repairing the route and can be immediately
forwarded. However, repairing the route before a data packet is forwarded. However, repairing the route before a data packet is
received for it runs the risk of repairing routes that are no longer received for it runs the risk of repairing routes that are no longer
in use. Therefore, depending upon the local traffic in the network in use. Therefore, depending upon the local traffic in the network
and whether congestion is being experienced, the node MAY elect to and whether congestion is being experienced, the node MAY elect to
proactively repair the routes before a data packet is received; proactively repair the routes before a data packet is received;
otherwise, it can wait until a data is received, and then commence otherwise, it can wait until a data is received, and then commence
the repair of the route. the repair of the route.
5.13. Actions After Reboot 6.13. Actions After Reboot
A node participating in the ad hoc network must take certain actions A node participating in the ad hoc network must take certain actions
after reboot as it might lose all sequence number records for all after reboot as it might lose all sequence number records for all
destinations, including its own sequence number. However, there destinations, including its own sequence number. However, there
may be neighboring nodes that are using this node as an active next may be neighboring nodes that are using this node as an active
hop. This can potentially create routing loops. To prevent this next hop. This can potentially create routing loops. To prevent
possibility, each node on reboot waits for DELETE_PERIOD. During this this possibility, each node on reboot waits for DELETE_PERIOD
time, the node does not transmit any RREP messages. If the node before transmitting any route discovery messages. If the node
receives a RREQ, RREP, or RERR control packet, it SHOULD create route receives a RREQ, RREP, or RERR control packet, it SHOULD create route
entries as appropriate given the sequence number information in the entries as appropriate given the sequence number information in the
control packets, but MUST not forward any control packets. If the control packets, but MUST not forward any control packets. If the
node receives a data packet for some other destination, it SHOULD node receives a data packet for some other destination, it SHOULD
broadcast a RERR as described in subsection 5.11 and MUST reset the broadcast a RERR as described in subsection 6.11 and MUST reset the
waiting timer to expire after current time plus DELETE_PERIOD. waiting timer to expire after current time plus DELETE_PERIOD.
It can be shown [1] that by the time the rebooted node comes out of It can be shown [4] that by the time the rebooted node comes out
the waiting phase and becomes an active router again, none of its of the waiting phase and becomes an active router again, none of
neighbors will be using it as an active next hop any more. Its own its neighbors will be using it as an active next hop any more. Its
sequence number gets updated once it receives a RREQ from any other own sequence number gets updated once it receives a RREQ from any
node, as the RREQ always carries the maximum destination sequence other node, as the RREQ always carries the maximum destination
number seen en route. sequence number seen en route. If no such RREQ arrives, the node
MUST initialize its own sequence number to zero.
5.14. Interfaces 6.14. Interfaces
Because AODV should operate smoothly over wired, as well as wireless, Because AODV should operate smoothly over wired, as well as wireless,
networks, and because it is likely that AODV will also be used with networks, and because it is likely that AODV will also be used with
multi-homed radios, the interface over which packets arrive must multiple wireless devices, the particular interface over which
be known to AODV whenever a packet is received. This includes the packets arrive must be known to AODV whenever a packet is received.
reception of RREQ, RREP, and RERR messages. Whenever a packet is This includes the reception of RREQ, RREP, and RERR messages.
received from a new neighbor, the interface on which that packet was Whenever a packet is received from a new neighbor, the interface
received is recorded into the route table entry for that neighbor, on which that packet was received is recorded into the route table
along with all the other appropriate routing information. Similarly, entry for that neighbor, along with all the other appropriate routing
whenever a route to a new destination is learned, the interface information. Similarly, whenever a route to a new destination is
through which the destination can be reached is also recorded into learned, the interface through which the destination can be reached
the destination's route table entry. is also recorded into the destination's route table entry.
When multiple interfaces are available, a node retransmitting a RREQ When multiple interfaces are available, a node retransmitting a RREQ
message rebroadcasts that message on all interfaces that have been message rebroadcasts that message on all interfaces that have been
configured for operation in the ad-hoc network, except those on which configured for operation in the ad-hoc network, except those on which
it is known that all of the nodes neighbors have already received it is known that all of the nodes neighbors have already received
the RREQ For instance, for some broadcast media (e.g., Ethernet) it the RREQ For instance, for some broadcast media (e.g., Ethernet) it
may be presumed that all nodes on the same link receive a broadcast may be presumed that all nodes on the same link receive a broadcast
message at the same time. When a node needs to transmit a RERR, it message at the same time. When a node needs to transmit a RERR, it
SHOULD only transmit it on those interfaces that have precursor nodes SHOULD only transmit it on those interfaces that have neighboring
for that route. precursor nodes for that route.
6. AODV and Aggregated Networks 7. AODV and Aggregated Networks
AODV has been designed for use by mobile nodes with IP addresses AODV has been designed for use by mobile nodes with IP addresses
that are not necessarily related to each other, to create an ad hoc that are not necessarily related to each other, to create an ad hoc
network. However, in some cases a collection of mobile nodes MAY network. However, in some cases a collection of mobile nodes MAY
operate in a fixed relationship to each other and share a common operate in a fixed relationship to each other and share a common
subnet prefix, moving together within an area where an ad hoc network subnet prefix, moving together within an area where an ad hoc network
has formed. Call such a collection of nodes a ``subnet''. In this has formed. Call such a collection of nodes a ``subnet''. In this
case, it is possible for a single node within the subnet to advertise case, it is possible for a single node within the subnet to advertise
reachability for all other nodes on the subnet, by responding with reachability for all other nodes on the subnet, by responding with
a RREP message to any RREQ message requesting a route to any node a RREP message to any RREQ message requesting a route to any node
with the subnet routing prefix. Call the single node the ``subnet with the subnet routing prefix. Call the single node the ``subnet
router''. In order for a subnet router to operate the AODV protocol router''. In order for a subnet router to operate the AODV protocol
for the whole subnet, it has to maintain a destination sequence for the whole subnet, it has to maintain a destination sequence
number for the entire subnet. In any such RREP message sent by the number for the entire subnet. In any such RREP message sent by the
subnet router, the Prefix Size field of the RREP message MUST be subnet router, the Prefix Size field of the RREP message MUST be
set to the length of the subnet prefix. Other nodes sharing the set to the length of the subnet prefix. Other nodes sharing the
subnet prefix SHOULD NOT issue RREP messages, and SHOULD forward RREQ subnet prefix SHOULD NOT issue RREP messages, and SHOULD forward RREQ
messages to the subnet leader. messages to the subnet router.
The processing for RREPs that give routes to subnets (i.e., have
nonzero prefix length) is the same as processing for host-specific
RREP messages. Every node that receives the RREP with prefix size
information SHOULD create or update the route table entry for the
subnet, including the sequence number supplied by the subnet router,
and including the appropriate precursor information. Then, in the
future the node can use the information to avoid sending future RREQs
for other nodes on the same subnet.
When a node uses a subnet route it may be that a packet is routed to
an IP address on the subnet that is not assigned to any existing node
in the ad hoc network. When that happens, the subnet router MUST
return ICMP Host Unreachable message to the sending node. Upstream
nodes receiving such an ICMP message SHOULD record the information
that the partcular IP address is unreachable, but MUST NOT invalidate
the route entry for any matching subnet prefix.
If several nodes in the subnet advertise reachability to the subnet If several nodes in the subnet advertise reachability to the subnet
defined by the subnet prefix, the node with the lowest IP address defined by the subnet prefix, the node with the lowest IP address
is elected to be the subnet leader, and all other nodes MUST stop is elected to be the subnet router, and all other nodes MUST stop
advertising reachability. advertising reachability.
The behavior of default routes (i.e., routes with routing prefix The behavior of default routes (i.e., routes with routing prefix
length 0) is not defined in this specification. Selection of routes length 0) is not defined in this specification. Selection of routes
sharing prefix bits should be according to longest match first. sharing prefix bits should be according to longest match first.
7. Using AODV with Other Networks 8. Using AODV with Other Networks
In some configurations, an ad hoc network may be able to provide In some configurations, an ad hoc network may be able to provide
connectivity between external routing domains that do not use AODV. connectivity between external routing domains that do not use AODV.
If the points of contact to the other networks can act as subnet If the points of contact to the other networks can act as subnet
routers (see Section 6) for any relevant networks within the external routers (see Section 7) for any relevant networks within the external
routing domains, then the ad hoc network can maintain connectivity to routing domains, then the ad hoc network can maintain connectivity to
the external routing domains. Indeed, the external routing networks the external routing domains. Indeed, the external routing networks
can use the ad hoc network defined by AODV as a transit network. can use the ad hoc network defined by AODV as a transit network.
In order to provide this feature, a point of contact to an external In order to provide this feature, a point of contact to an external
network (call it an Infrastructure Router) has to act as the subnet network (call it an Infrastructure Router) has to act as the subnet
router for every subnet of interest within the external network for router for every subnet of interest within the external network for
which the Infrastructure Router can provide reachability. This which the Infrastructure Router can provide reachability. This
includes the need for maintaining a destination sequence number for includes the need for maintaining a destination sequence number for
that external subnet. that external subnet.
If multiple Infrastructure Routers offer reachability to the same If multiple Infrastructure Routers offer reachability to the same
external subnet, those Infrastructure Routers have to cooperate (by external subnet, those Infrastructure Routers have to cooperate (by
means outside the scope of this specification) to provide consistent means outside the scope of this specification) to provide consistent
AODV semantics for ad hoc access to those subnets. AODV semantics for ad hoc access to those subnets.
8. Extensions 9. Extensions
In this section, the format of extensions to the RREQ and RREP In this section, the format of extensions to the RREQ and RREP
messages is specified. All such extensions appear after the message messages is specified. All such extensions appear after the message
data, and have the following format: data, and have the following format:
0 1 2 3 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 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 ... | Type | Length | type-specific data ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
skipping to change at page 27, line 15 skipping to change at page 28, line 28
Type 1-255 Type 1-255
Length The length of the type-specific data, not including the Length The length of the type-specific data, not including the
Type and Length fields of the extension in bytes. Type and Length fields of the extension in bytes.
Extensions with types between 128 and 255 may NOT be skipped. The Extensions with types between 128 and 255 may NOT be skipped. The
rules for extensions will be spelled out more fully, and conform to rules for extensions will be spelled out more fully, and conform to
the rules for handling IPv6 options. the rules for handling IPv6 options.
8.1. Hello Interval Extension Format 9.1. Hello Interval Extension Format
0 1 2 3 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 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 | Hello Interval ... | | Type | Length | Hello Interval ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... Hello Interval, continued | | ... Hello Interval, continued |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type 2 Type 1
Length 4 Length 4
Hello Interval Hello Interval
The number of milliseconds between successive The number of milliseconds between successive
transmissions of a Hello message. transmissions of a Hello message.
The Hello Interval extension MAY be appended to a RREP message with The Hello Interval extension MAY be appended to a RREP message with
TTL == 1, to be used by a neighboring receiver in determine how long TTL == 1, to be used by a neighboring receiver in determine how long
to wait for subsequent such RREP messages (i.e., Hello messages; see to wait for subsequent such RREP messages (i.e., Hello messages; see
section 5.9). section 6.9).
9. Configuration Parameters 10. Configuration Parameters
This section gives default values for some important parameters This section gives default values for some important parameters
associated with AODV protocol operations. A particular mobile node associated with AODV protocol operations. A particular mobile node
may wish to change certain of the parameters, in particular the may wish to change certain of the parameters, in particular the
NET_DIAMETER, MY_ROUTE_TIMEOUT, ALLOWED_HELLO_LOSS, RREQ_RETRIES, NET_DIAMETER, MY_ROUTE_TIMEOUT, ALLOWED_HELLO_LOSS, RREQ_RETRIES,
and possibly the HELLO_INTERVAL. In the latter case, the node and possibly the HELLO_INTERVAL. In the latter case, the node
should advertise the HELLO_INTERVAL in its Hello messages, by should advertise the HELLO_INTERVAL in its Hello messages, by
appending a Hello Interval Extension to the RREP message. Choice appending a Hello Interval Extension to the RREP message. Choice
of these parameters may affect the performance of the protocol. of these parameters may affect the performance of the protocol.
Changing NODE_TRAVERSAL_TIME also changes the node's estimate Changing NODE_TRAVERSAL_TIME also changes the node's estimate
skipping to change at page 28, line 22 skipping to change at page 29, line 35
BLACKLIST_TIMEOUT RREQ_RETRIES * NET_TRAVERSAL_TIME BLACKLIST_TIMEOUT RREQ_RETRIES * NET_TRAVERSAL_TIME
DELETE_PERIOD see note below DELETE_PERIOD see note below
HELLO_INTERVAL 1,000 Milliseconds HELLO_INTERVAL 1,000 Milliseconds
LOCAL_ADD_TTL 2 LOCAL_ADD_TTL 2
MAX_REPAIR_TTL 0.3 * NET_DIAMETER MAX_REPAIR_TTL 0.3 * NET_DIAMETER
MIN_REPAIR_TTL see note below MIN_REPAIR_TTL see note below
MY_ROUTE_TIMEOUT 2 * ACTIVE_ROUTE_TIMEOUT MY_ROUTE_TIMEOUT 2 * ACTIVE_ROUTE_TIMEOUT
NET_DIAMETER 35 NET_DIAMETER 35
NET_TRAVERSAL_TIME 2 * NODE_TRAVERSAL_TIME * NET_DIAMETER NET_TRAVERSAL_TIME 2 * NODE_TRAVERSAL_TIME * NET_DIAMETER
NEXT_HOP_WAIT NODE_TRAVERSAL_TIME + 10 NEXT_HOP_WAIT NODE_TRAVERSAL_TIME + 10
NODE_TRAVERSAL_TIME 40 NODE_TRAVERSAL_TIME 40 milliseconds
PATH_DISCOVERY_TIME 2 * NET_TRAVERSAL_TIME PATH_DISCOVERY_TIME 2 * NET_TRAVERSAL_TIME
RERR_RATELIMIT 10 RERR_RATELIMIT 10
RING_TRAVERSAL_TIME 2 * NODE_TRAVERSAL_TIME * (TTL_VALUE + TIMEOUT_BUFFER) RING_TRAVERSAL_TIME 2 * NODE_TRAVERSAL_TIME *
(TTL_VALUE + TIMEOUT_BUFFER)
RREQ_RETRIES 2 RREQ_RETRIES 2
RREQ_RATELIMIT 10 RREQ_RATELIMIT 10
TIMEOUT_BUFFER 2 TIMEOUT_BUFFER 2
TTL_START 1 TTL_START 1
TTL_INCREMENT 2 TTL_INCREMENT 2
TTL_THRESHOLD 7 TTL_THRESHOLD 7
TTL_VALUE see note below TTL_VALUE see note below
The MIN_REPAIR_TTL should be the last known hop count to The MIN_REPAIR_TTL should be the last known hop count to
the destination. If Hello messages are used, then the the destination. If Hello messages are used, then the
ACTIVE_ROUTE_TIMEOUT parameter value MUST be more than the ACTIVE_ROUTE_TIMEOUT parameter value MUST be more than the
value (ALLOWED_HELLO_LOSS * HELLO_INTERVAL). value (ALLOWED_HELLO_LOSS * HELLO_INTERVAL). For a given
ACTIVE_ROUTE_TIMEOUT value, this may require some adjustment to
the value of the HELLO_INTERVAL, and consequently use of the Hello
Interval Extension in the Hello messages.
TTL_VALUE is the value of the TTL field in the IP header while the TTL_VALUE is the value of the TTL field in the IP header while the
expanding ring search is being performed. This is described further expanding ring search is being performed. This is described further
in section 5.4. The TIMEOUT_BUFFER is configurable. Its purpose is in section 6.4. The TIMEOUT_BUFFER is configurable. Its purpose is
to provide a buffer for the timeout so that if the RREP is delayed to provide a buffer for the timeout so that if the RREP is delayed
due to congestion, a timeout is less likely to occur while the RREP due to congestion, a timeout is less likely to occur while the RREP
is still en route back to the source. To omit this buffer, set is still en route back to the source. To omit this buffer, set
TIMEOUT_BUFFER = 0. TIMEOUT_BUFFER = 0.
DELETE_PERIOD should be an upper bound on the time for which an DELETE_PERIOD is intended to provide an upper bound on the time
upstream node A can have a neighbor B as an active next hop for for which an upstream node A can have a neighbor B as an active
destination D, while B has invalidated the route to D. Beyond this next hop for destination D, while B has invalidated the route to
time B can delete the route to D. The determination of the upper D. Beyond this time B can delete the (already invalidated) route
bound somewhat depends on the characteristics of the underlying to D. The determination of the upper bound depends somewhat on the
link layer. If Hello messages are used to determine the continued characteristics of the underlying link layer. If Hello messages
availability of links to next hop nodes, DELETE_PERIOD must be at are used to determine the continued availability of links to next
least ALLOWED_HELLO_LOSS * HELLO_INTERVAL. If the link layer feedback hop nodes, DELETE_PERIOD must be at least ALLOWED_HELLO_LOSS *
is used to detect loss of link, DELETE_PERIOD must be at least HELLO_INTERVAL. If the link layer feedback is used to detect loss
ACTIVE_ROUTE_TIMEOUT. If hello messages are received from a neighbor of link, DELETE_PERIOD must be at least ACTIVE_ROUTE_TIMEOUT. If
but data packets to that neighbor are lost, (due to temporary link hello messages are received from a neighbor but data packets to that
asymmetry, e.g.) we have to make more concrete assumptions about neighbor are lost, (due to temporary link asymmetry, e.g.) we have
the underlying link layer. We assume that such asymmetry cannot to make more concrete assumptions about the underlying link layer.
persist beyond a certain time, say, a multiple K of HELLO_INTERVAL. We assume that such asymmetry cannot persist beyond a certain time,
In other words, a node will invariably receive at least one out say, a multiple K of HELLO_INTERVAL. In other words, a node will
of K subsequent Hello messages from a neighbor if the link is invariably receive at least one out of K subsequent Hello messages
working and the neighbor is sending no other traffic. Covering all from a neighbor if the link is working and the neighbor is sending no
possibilities, other traffic. Covering all possibilities,
DELETE_PERIOD = K * max (ACTIVE_ROUTE_TIMEOUT, HELLO_INTERVAL) (K = 5 is DELETE_PERIOD = K * max (ACTIVE_ROUTE_TIMEOUT, HELLO_INTERVAL)
recommended). (K = 5 is recommended).
NET_DIAMETER measures the maximum possible number of hops between NET_DIAMETER measures the maximum possible number of hops between
two nodes in the network. NODE_TRAVERSAL_TIME is a conservative two nodes in the network. NODE_TRAVERSAL_TIME is a conservative
estimate of the average one hop traversal time for packets and should estimate of the average one hop traversal time for packets and should
include queuing delays, interrupt processing times and transfer include queuing delays, interrupt processing times and transfer
times. ACTIVE_ROUTE_TIMEOUT SHOULD be set to a longer value (at times. ACTIVE_ROUTE_TIMEOUT SHOULD be set to a longer value (at
least 10,000 milliseconds) if link-layer indications are used to least 10,000 milliseconds) if link-layer indications are used to
detect link breakages such as in IEEE 802.11 [4] standard. TTL_START detect link breakages such as in IEEE 802.11 [5] standard. TTL_START
should be set to at least 2 if Hello messages are used for local should be set to at least 2 if Hello messages are used for local
connectivity information. Performance of the AODV protocol is connectivity information. Performance of the AODV protocol is
sensitive to the chosen values of these constants, which often depend sensitive to the chosen values of these constants, which often depend
on the characteristics of the underlying link layer protocol, radio on the characteristics of the underlying link layer protocol, radio
technologies etc. BLACKLIST_TIMEOUT should be suitably increased technologies etc. BLACKLIST_TIMEOUT should be suitably increased
if an expanding ring search is used. In such cases, it should be if an expanding ring search is used. In such cases, it should be
[(TTL_THRESHOLD - TTL_START)/TTL_INCREMENT] + 1 + RREQ_RETRIES * {[(TTL_THRESHOLD - TTL_START)/TTL_INCREMENT] + 1 + RREQ_RETRIES} *
NET_TRAVERSAL_TIME. This is to account for possible additional route NET_TRAVERSAL_TIME. This is to account for possible additional route
discovery attempts. discovery attempts.
10. Security Considerations 11. Security Considerations
Currently, AODV does not specify any special security measures. Currently, AODV does not specify any special security measures.
Route protocols, however, are prime targets for impersonation Route protocols, however, are prime targets for impersonation
attacks. If there is danger of such attacks, AODV control messages attacks. In networks where the node membership is not known, it
must be protected by use of authentication techniques, such as those is difficult to determine the occurrence of impersonation attacks,
involving generation of unforgeable and cryptographically strong and security prevention techniques are difficult at best. However,
message digests or digital signatures. In particular, RREP messages when the network membership is known and there is a danger of
SHOULD be authenticated to avoid creation of spurious routes to a such attacks, AODV control messages must be protected by use of
desired destination. Otherwise, an attacker could masquerade as the authentication techniques, such as those involving generation
desired destination, and maliciously deny service to the destination of unforgeable and cryptographically strong message digests or
and/or maliciously inspect and consume traffic intended for delivery digital signatures. While AODV does not place restrictions on the
to the destination. RERR messages, while less dangerous, SHOULD be authentication mechanism used for this purpose, IPsec AH is an
authenticated in order to prevent malicious nodes from disrupting appropriate choice for cases where the nodes share an appropriate
valid routes between nodes that are communication partners. security association that enables the use of AH.
Since AODV does not make any assumption about the nature of the In particular, RREP messages SHOULD be authenticated to avoid
address assignment to the mobile nodes except that they are presumed creation of spurious routes to a desired destination. Otherwise, an
to have unique IP addresses, no definite statements can be made about attacker could masquerade as the desired destination, and maliciously
the applicability of IPsec authentication headers or key exchange deny service to the destination and/or maliciously inspect and
mechanisms. However, if the mobile nodes in the ad hoc network have consume traffic intended for delivery to the destination. RERR
pre-established security associations, they should be able to use the messages, while less dangerous, SHOULD be authenticated in order to
same authentication mechanisms based on their IP addresses as they prevent malicious nodes from disrupting valid routes between nodes
would have used otherwise. that are communication partners.
11. IPv6 Considerations AODV does not make any assumption about the method by which addresses
are assigned to the mobile nodes, except that they are presumed to
have unique IP addresses. Therefore, no special consideration, other
than what is natural because of the general protocol specifications,
can be made about the applicability of IPsec authentication headers
or key exchange mechanisms. However, if the mobile nodes in the
ad hoc network have pre-established security associations, it is
presumed that the purposes for which the security associations are
created include that of authorizing the processing of AODV control
messages. 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.
12. IANA Considerations
AODV defines a "Type" field for messages sent to port 654. A new
registry is to be created for the values for this Type field, and the
following values assigned:
Message Type Value
--------------------------- -----
Route Request (RREQ) 1
Route Reply (RREP) 2
Route Error (RERR) 3
Route-Reply Ack (RREP-ACK) 4
AODV control messages can have extensions. Currently, only one
extension is defined. A new registry is to be created for the Type
field of the extensions:
Extension Type Value
--------------------------- -----
Hello Interval 1
Future values of the Message Type or Extension Type can be allocated
using standards action [2].
13. IPv6 Considerations
See [6] for detailed operation for IPv6. The only changes to the See [6] for detailed operation for IPv6. The only changes to the
protocol are that the address fields are enlarged. protocol are that the address fields are enlarged.
12. Acknowledgments 14. Acknowledgments
Special thanks to Ian Chakeres, UCSB, for his extensive suggestions Special thanks to Ian Chakeres, UCSB, for his extensive suggestions
and contributions to this revision. and contributions to recent revisions.
We acknowledge with gratitude the work done at University of We acknowledge with gratitude the work done at University of
Pennsylvania within Carl Gunter's group, as well as at Stanford and Pennsylvania within Carl Gunter's group, as well as at Stanford and
CMU, to determine some conditions (especially involving reboots and CMU, to determine some conditions (especially involving reboots and
lost RERRs) under which previous versions of AODV could suffer from lost RERRs) under which previous versions of AODV could suffer from
routing loops. Contributors to those efforts include Karthikeyan routing loops. Contributors to those efforts include Karthikeyan
Bhargavan, Joshua Broch, Dave Maltz, Madanlal Musuvathi, and Bhargavan, Joshua Broch, Dave Maltz, Madanlal Musuvathi, and
Davor Obradovic. The idea of a DELETE_PERIOD, for which expired Davor Obradovic. The idea of a DELETE_PERIOD, for which expired
routes (and, in particular, the sequence numbers) to a particular routes (and, in particular, the sequence numbers) to a particular
destination must be maintained, was also suggested by them. destination must be maintained, was also suggested by them.
We also acknowledge the comments and improvements suggested by We also acknowledge the comments and improvements suggested by
Sung-Ju Lee (especially regarding local repair), Mahesh Marina, Erik Sung-Ju Lee (especially regarding local repair), Mahesh Marina, Erik
Nordstrom (who provided text for section 5.11), Yves Prelot, Marc Nordstrom (who provided text for section 6.11), Yves Prelot, Marc
Mosko, Manel Guerrero Zapata, Philippe Jacquet, and Fred Baker. Mosko, Manel Guerrero Zapata, Philippe Jacquet, and Fred Baker.
References References
[1] Karthikeyan Bhargavan, Carl A. Gunter, and Davor Obradovic. [1] S. Bradner. Key words for use in RFCs to Indicate Requirement
Fault Origin Adjudication. In Proceedings of the Workshop on
Formal Methods in Software Practice, Portland, OR, August 2000.
[2] S. Bradner. Key words for use in RFCs to Indicate Requirement
Levels. Request for Comments (Best Current Practice) 2119, Levels. Request for Comments (Best Current Practice) 2119,
Internet Engineering Task Force, March 1997. Internet Engineering Task Force, March 1997.
[2] T. Narten and H. Alvestrand. Guidelines for Writing an IANA
Considerations Section in RFCs. Request for Comments (Best
Current Practice) 2434, Internet Engineering Task Force, October
1998.
[3] J. Manner et al. Mobility Related Terminology (work in [3] J. Manner et al. Mobility Related Terminology (work in
progress). draft-manner-seamoby-terms-02.txt, July 2001. progress). draft-manner-seamoby-terms-02.txt, July 2001.
[4] IEEE 802.11 Committee, AlphaGraphics #35, 10201 N.35th Avenue, [4] Karthikeyan Bhargavan, Carl A. Gunter, and Davor Obradovic.
Fault Origin Adjudication. In Proceedings of the Workshop on
Formal Methods in Software Practice, Portland, OR, August 2000.
[5] IEEE 802.11 Committee, AlphaGraphics #35, 10201 N.35th Avenue,
Phoenix AZ 85051. Wireless LAN Medium Access Control MAC and Phoenix AZ 85051. Wireless LAN Medium Access Control MAC and
Physical Layer PHY Specifications, June 1997. IEEE Standard Physical Layer PHY Specifications, June 1997. IEEE Standard
802.11-97. 802.11-97.
[5] D. Mills. Simple Network Time Protocol (SNTP) Version 4 for [6] C. Perkins, E. Royer, and S. Das. Ad hoc on demand distance
IPv4, IPv6 and OSI. Request for Comments (Informational) 2030, vector (AODV) routing for ip version 6 (work in progress).
Internet Engineering Task Force, October 1996. Internet Draft, Internet Engineering Task Force, November 2001.
[6] C. Perkins, E. Royer, and S. Das. Ad Hoc On Demand Distance References [1] and [2] are normative; all others are informative.
Vector (AODV) Routing for IP version 6 (work in progress).
Internet Draft, Internet Engineering Task Force.
draft-perkins-manet-aodv6-01.txt, November 2001.
A. Draft Modifications A. Draft Modifications
The following are major changes between this version (12) of the AODV The following are major changes between this version (13) of the AODV
draft and the previous version (11): draft and previous versions:
- Added binary exponential backoff to repeated RREQ attempts - RERR clarifications for handling subnet routes. A processing
for the same destination. step was added to eliminate host routes that are redundant with
subnet routes.
- Included a mechanism for dynamically calculating the waiting - Added explicit specification to clarify that subnet routes are
time for a RREP during an expanding ring search. This includes the handled the same way as host routes for managing timeouts and
addition of a new parameter, RING_TRAVERSAL_TIME. route table entries.
- Added the TTL_VALUE and TIMEOUT_BUFFER parameters to help - Applicability Statement and IANA Considerations sections added.
dynamically calculate the waiting time for a RREP during an
expanding ring search.
- Clarified the option of proactive local repair for recently - Normative References placed at beginning of bibliography.
broken routes.
- Updated Security Considerations section. AH is suggested but not
mandated as a good choice for authenticating control messages.
- Updated the AODV and Aggregated Networks section to include the
transmission of an ICMP Host Unreachable message for data packets
sent to non-existent destinations.
Author's Addresses Author's Addresses
Questions about this memo can be directed to: Questions about this memo can be directed to:
Charles E. Perkins Charles E. Perkins
Communications Systems Laboratory Communications Systems Laboratory
Nokia Research Center Nokia Research Center
313 Fairchild Drive 313 Fairchild Drive
Mountain View, CA 94303 Mountain View, CA 94303
 End of changes. 

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