draft-ietf-manet-aodv-10.txt   draft-ietf-manet-aodv-11.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
19 January 2002 Elizabeth M. Belding-Royer 19 June 2002 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-10.txt draft-ietf-manet-aodv-11.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@itd.nrl.navy.mil 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
all provisions of Section 10 of RFC2026. Internet-Drafts are working all provisions of Section 10 of RFC2026. Internet-Drafts are working
documents of the Internet Engineering Task Force (IETF), its areas, documents of the Internet Engineering Task Force (IETF), its areas,
and its working groups. Note that other groups may also distribute and its working groups. Note that other groups may also distribute
working documents as Internet-Drafts. working documents as Internet-Drafts.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
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 4 4. Message Formats 5
4.1. Route Request (RREQ) Message Format . . . . . . . . . . . 4 4.1. Route Request (RREQ) Message Format . . . . . . . . . . . 5
4.2. Route Reply (RREP) Message Format . . . . . . . . . . . . 5 4.2. Route Reply (RREP) Message Format . . . . . . . . . . . . 6
4.3. Route Error (RERR) Message Format . . . . . . . . . . . . 7 4.3. Route Error (RERR) Message Format . . . . . . . . . . . . 8
4.4. Route Reply Acknowledgment (RREP-ACK) Message Format . . 9
5. Route Reply Acknowledgment (RREP-ACK) Message Format 8 5. AODV Operation 9
5.1. Maintaining Sequence Numbers . . . . . . . . . . . . . . 9
5.2. Route Table Entries and Precursor Lists . . . . . . . . . 11
5.3. Generating Route Requests . . . . . . . . . . . . . . . . 12
5.4. Controlling Dissemination of Route Request Messages . . . 13
5.5. Processing and Forwarding Route Requests . . . . . . . . 13
5.6. Generating Route Replies . . . . . . . . . . . . . . . . 15
5.6.1. Route Reply Generation by the Destination . . . . 15
5.6.2. Route Reply Generation by an Intermediate Node . 16
5.6.3. Generating Gratuitous RREPs . . . . . . . . . . . 16
5.7. Receiving and Forwarding Route Replies . . . . . . . . . 17
5.8. Operation over Unidirectional Links . . . . . . . . . . . 18
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 . . . . . . . . . . . . . . . . . . . . . . 22
5.13. Actions After Reboot . . . . . . . . . . . . . . . . . . 24
5.14. Interfaces . . . . . . . . . . . . . . . . . . . . . . . 24
6. AODV Operation 8 6. AODV and Aggregated Networks 25
6.1. Maintaining Sequence Numbers . . . . . . . . . . . . . . 8
6.2. Maintaining Route Table Entries and Precursor Lists . . . 10
6.3. Generating Route Requests . . . . . . . . . . . . . . . . 10
6.4. Controlling Dissemination of Route Request Messages . . . 11
6.5. Processing and Forwarding Route Requests . . . . . . . . 12
6.6. Generating Route Replies . . . . . . . . . . . . . . . . 14
6.6.1. Route Reply Generation by the Destination . . . . 14
6.6.2. Route Reply Generation by an Intermediate Node . 14
6.6.3. Generating Gratuitous RREPs . . . . . . . . . . . 15
6.7. Receiving and Forwarding Route Replies . . . . . . . . . 16
6.8. Operation over Unidirectional Links . . . . . . . . . . . 17
6.9. Hello Messages . . . . . . . . . . . . . . . . . . . . . 17
6.10. Maintaining Local Connectivity . . . . . . . . . . . . . 18
6.11. Route Error Messages, Route Expiry and Route Deletion . 19
6.12. Local Repair . . . . . . . . . . . . . . . . . . . . . . 20
6.13. Actions After Reboot . . . . . . . . . . . . . . . . . . 22
6.14. Interfaces . . . . . . . . . . . . . . . . . . . . . . . 22
7. AODV and Aggregated Networks 23 7. Using AODV with Other Networks 25
8. Using AODV with Other Networks 23 8. Extensions 26
8.1. Hello Interval Extension Format . . . . . . . . . . . . . 26
9. Extensions 24 9. Configuration Parameters 27
9.1. Hello Interval Extension Format . . . . . . . . . . . . . 24
9.2. Timestamp Extension Format . . . . . . . . . . . . . . . 25
10. Configuration Parameters 25 10. Security Considerations 28
11. Security Considerations 27 11. IPv6 Considerations 29
12. Acknowledgments 28 12. Acknowledgments 29
A. Draft Modifications 29 A. Draft Modifications 31
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
broken 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 for any route information it
sends to requesting nodes. Using destination sequence numbers sends to requesting nodes. Using destination sequence numbers
ensures loop freedom and is simple to program. Given the choice ensures loop freedom and is simple to program. Given the choice
between two routes to a destination, a requesting node always selects between two routes to a destination, a requesting node always selects
the one with the greatest sequence number. 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 (RERRs) are the message types defined by AODV. These message types
types are received at port 654, over UDP, and normal IP header are received via UDP, and normal IP header processing applies.
processing applies. So, for instance, the requesting node is So, for instance, the requesting node is expected to use its IP
expected to use its IP address as the Originator IP address for the address as the Originator IP address for the messages. For broadcast
messages. For broadcast messages, the IP limited broadcast address messages, the IP limited broadcast address (255.255.255.255) is used.
(255.255.255.255) is used. This means that such messages are not This means that such messages are not blindly forwarded. However,
blindly forwarded. However, AODV operation does require certain AODV operation does require certain messages (e.g., RREQ) to be
messages (e.g., RREQ) to be disseminated widely, perhaps throughout disseminated widely, perhaps throughout the ad hoc network. The
the ad hoc network. The range of dissemination of such RREQs is range of dissemination of such RREQs is indicated by the TTL in the
indicated by the TTL in the IP header. Fragmentation is typically IP header. Fragmentation is typically not required.
not required.
As long as the endpoints of a communication connection have valid As long as the endpoints of a communication connection have valid
routes to each other, AODV does not play any role. When a route to a routes to each other, AODV does not play any role. When a route to a
new destination is needed, the node broadcasts a RREQ to find a route new destination is needed, the node broadcasts a RREQ to find a route
to the destination. A route can be determined when the RREQ reaches to the destination. A route can be determined when the RREQ reaches
either the destination itself, or an intermediate node with a 'fresh either the destination itself, or an intermediate node with a 'fresh
enough' route to the destination. A 'fresh enough' route is an enough' route to the destination. A 'fresh enough' route is a valid
unexpired route entry for the destination whose associated sequence route entry for the destination whose associated sequence number is
number is at least as great as that contained in the RREQ. The route at least as great as that contained in the RREQ. The route is made
is made available by unicasting a RREP back to the origination of available by unicasting a RREP back to the origination of the RREQ.
the RREQ. Each node receiving the request caches a route back to the Each node receiving the request caches a route back to the originator
originator of the request, so that the RREP can be unicast from the of the request, so that the RREP can be unicast from the destination
destination along a path to that originator, or likewise from any along a path to that originator, or likewise from any intermediate
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 which are now unreachable due to
the loss of the link. In order to enable this reporting mechanism, the loss of the link. In order to enable this reporting mechanism,
each node keeps a ``precursor list'', containing the IP address for each node keeps a ``precursor list'', containing the IP address for
each its neighbors that are likely to use it as a next hop towards each its neighbors that are likely to use it as a next hop towards
the destination that is now unreachable. The information in the the destination that is now unreachable. The information in the
precursor lists is most easily acquired during the processing for precursor lists is most easily acquired during the processing for
generation of a RREP message, which by definition has to be sent to a generation of a RREP message, which by definition has to be sent to a
node in a precursor list (see section 6.6). node in a precursor list (see section 5.6).
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 ephemeral 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
- Vaild Destination Sequence Number
- Interface - Interface
- Hop Count (number of hops needed to reach destination) - Hop Count (number of hops needed to reach destination)
- Last Hop Count (described in subsections 6.4 and 6.11)
- Next Hop - Next Hop
- List of Precursors (described in Section 6.2) - List of Precursors (described in Section 5.2)
- Lifetime (expiration or deletion time of the route) - Lifetime (expiration or deletion time of the route)
- Routing Flags - 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 metric (hop count). See section 6.1 for the sequence number and marking the route table entry state as
details. invalid. See section 5.1 for details.
3. AODV Terminology 3. AODV Terminology
This protocol specification uses conventional meanings [2] for This protocol specification uses conventional meanings [2] 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 routing table entry with a finite metric in the Hop Count A route towards a destination that has a routing table entry
field. A routing table may contain entries that are not active that is marked as valid. Only active routes can be used to
(invalid routes or entries). They have an infinite metric forward data packets.
in the Hop Count field. Only active entries can be used to
forward data packets. Invalid entries are eventually deleted.
broadcast broadcast
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
An IP address to which data packets are to be transmitted.
Same as "destination node". A node knows it is the destination
node for a data packet when its address appears in the
appropriate field of the IP header. Routes for destination
nodes are supplied by action of the AODV protocol, which
carries the IP address of the destination node in route
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
A route that has expired, denoted by a state of invalid in
the routing table. An invalid route is used to store the
previously valid route information for an extended period
of time. An invalid route may not be used to forward data
packets.
originating node originating node
A node that initiates an AODV message to be processed and A node that initiates an AODV message to be processed and
possibly retransmitted by other nodes in the ad hoc network. possibly retransmitted by other nodes in the ad hoc network.
For instance, the node initiating a Route Discovery process and For instance, the node initiating a Route Discovery process and
broadcasting the RREQ message is called the originating node of broadcasting the RREQ message is called the originating node of
the RREQ message. 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
An increasing number maintained by each originating node. When
used in control messages it is used by other nodes to determine
the freshness of the information contained from the originating
node.
valid route
See active route.
4. Message Formats 4. Message Formats
4.1. Route Request (RREQ) Message Format 4.1. 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| Reserved | Hop Count | | Type |J|R|G|D|U| Reserved | Hop Count |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RREQ ID | | RREQ ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Destination IP Address | | Destination IP Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Destination Sequence Number | | Destination Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Originator IP Address | | Originator IP Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Originator Sequence Number | | Originator Sequence Number |
skipping to change at page 5, line 8 skipping to change at page 5, line 37
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 6.3, 6.6.3) sections 5.3, 5.6.3)
D Destination only flag; indicates only the
destination may respond to this RREQ (see
section 5.5).
U Unknown sequence number; indicates the destination
sequence number is unknown(see section 5.3).
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.
skipping to change at page 6, line 4 skipping to change at page 6, line 38
| 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Originator IP address | | Originator IP address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 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 5 and 6.7. A Acknowledgment required; see sections 4.4 and 5.7.
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 6, line 37 skipping to change at page 7, line 24
is supplied. is supplied.
Destination Sequence Number Destination Sequence Number
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 for which nodes receiving the RREP consider Lifetime The time in milliseconds for which nodes receiving
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 Leader 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 Leader 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 Leader has to
guarantee reachability to all the hosts sharing the indicated subnet guarantee reachability to all the hosts sharing the indicated subnet
prefix. The Subnet Leader is also responsible for maintaining the prefix. The Subnet Leader is also responsible for maintaining the
Destination Sequence Number for the whole subnet. See section 7 for Destination Sequence Number for the whole subnet. See section 6 for
details. details.
The 'A' bit is used in cases where the link over which the RREP
message is sent may be unreliable or unidirectional. When the
RREP message contains the 'A' bit set, the receiver of the RREP is
expected to return a RREP-ACK message. See section 5.8.
4.3. Route Error (RERR) Message Format 4.3. 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 7, line 46 skipping to change at page 8, line 46
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 6.2 for information about how to maintain the appropriate See section 5.2 for information about how to maintain the appropriate
records for this determination, and section 6.11 for specification records for this determination, and section 5.11 for specification
about how to create the list of destinations. about how to create the list of destinations.
5. Route Reply Acknowledgment (RREP-ACK) Message Format 4.4. Route Reply Acknowledgment (RREP-ACK) Message Format
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.
This is typically done when there is danger of unidirectional
links preventing the completion of a Route Discovery cycle (see
section 5.8).
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.
The RREP-ACK message may be used to acknowledge receipt of a RREP 5. AODV Operation
message. It is used in cases where the link over which the RREP
message is sent may be unreliable or unidirectional.
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.
6.1. Maintaining Sequence Numbers 5.1. Maintaining Sequence Numbers
AODV depends on each node in the network to own and maintain a Every route table entry at every node MUST include the latest
sequence number to guarantee the loop-freedom of all routes towards information available about the sequence number for the IP address of
that node. A node increments its own sequence number in two the destination node for which the route table entry is maintained.
This sequence number is called the "destination sequence number". It
is updated whenever a node receives new (i.e., not stale) information
about the sequence number from RREQ, RREP, or RERR messages that
may be received related to that destination. AODV depends on each
node in the network to own and maintain its destination sequence
number to guarantee the loop-freedom of all routes towards that
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 problems with
deleted reverse routes to the originator of a RREQ. deleted reverse routes to 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 by When the destination increments its sequence number, it MUST do so by
treating the sequence number value as if it were an unsigned number. treating the sequence number value as if it were an unsigned number.
Thus, if the sequence number has already been assigned to be the To accomplish sequence number rollover, if the sequence number has
largest possible number representable as a 32-bit unsigned integer already been assigned to be the largest possible number representable
(i.e., 4294967295), then when it is incremented it will then have a as a 32-bit unsigned integer (i.e., 4294967295), then when it is
value of zero (0). Similarly, if the sequence number currently has incremented it will then have a value of zero (0). On the other
the value 2147483647, which is the largest possible positive integer hand, if the sequence number currently has the value 2147483647,
when if 2's complement arithmetic is in use, the next value will be which is the largest possible positive integer if 2's complement
arithmetic is in use with 32-bit integers, the next value will be
2147483648, which is the most negative possible integer in the same 2147483648, which is the most negative possible integer in the same
numbering system. The representation of negative numbers is not numbering system. The representation of negative numbers is not
relevant to the incrementation of AODV sequence numbers. This is relevant to the incrementation of AODV sequence numbers. This is
in contrast to the manner in which the result of comparing two AODV in contrast to the manner in which the result of comparing two AODV
sequence numbers is to be treated (see below). sequence numbers is to be treated (see below).
Every route table entry at every node MUST include the latest In order to ascertain that information about a destination is not
information available about the sequence number for the IP address of stale, the node compares its current numerical value for the sequence
the destination node for which the route table entry is maintained. number with that obtained from the incoming AODV message. This
This sequence number is called the "destination sequence number". It comparison MUST be done using signed 32-bit arithmetic, this is
is updated whenever a node receives new (i.e., not stale) information necessary to accomplish sequence number rolloever. If the result of
about the sequence number from RREQ, RREP, or RERR messages that may subtracting the currently stored sequence number from the value of
be received related to that destination. In order to ascertain that the incoming sequence number is less than zero, then the information
information about a destination is not stale, the node compares its related to that destination in the AODV message MUST be discarded,
current numerical value for the sequence number with that obtained since that information is stale compared to the node's currently
from the incoming AODV message. This comparison MUST be done using stored information.
signed 32-bit arithmetic. If the result of subtracting the currently
stored sequence number from the value of the incoming sequence number
is less than zero, then the information related to that destination
in the AODV message MUST be discarded, since that information is
stale compared to the node's currently 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 in destination sequence number in one of its route table entries is
response to a broken 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 broken 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 puts the Hop Count to be "infinity" (for the case of number and marks the route as invalid (see also sections 5.11, 5.12).
broken links, see also see sections 6.11, 6.12). Whenever any fresh enough (i.e., containing a sequence number at
least equal to the recorded sequence number) routing information for
an affected destination is received by a node that has marked that
route table entry as invalid, the node SHOULD update its route table
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.
6.2. Maintaining Route Table Entries and Precursor Lists 5.2. Route Table Entries and Precursor Lists
For each valid route maintained by a node (containing a finite Hop
Count metric) as a routing table entry, the node also maintains a
list of precursors that may be forwarding packets on this route.
These precursors will receive notifications 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 neighboring nodes
to which a route reply was generated or forwarded.
When a node receives an AODV control packet from a neighbor, it When a node receives an AODV control packet from a neighbor, or
checks its route table for an entry for that neighbor. In the event creates or updates a route for a particular destination, it checks
that there is no corresponding entry for that neighbor, an entry its route table for an entry for the destination. In the event
that there is no corresponding entry for that destination, an entry
is created. The sequence number is either determined from the is created. The sequence number is either determined from the
information contained in the control packet (i.e., the neighbor is information contained in the control packet, or else the valid
the originator of a RREQ), or else it is initialized to zero if the sequence number field is set to false. The route is only updated if
sequence number for that node can not be determined. The Lifetime the new sequence number is either
field of the routing table entry is either determined from the
control packet (i.e., the neighbor is the originator of a RREP for
itself), or it is initialized to ALLOWED_HELLO_LOSS * HELLO_INTERVAL.
In other words, the reception of a control packet has the same
meaning as the reception of an explicit Hello message, in that it
signifies an active connection to that neighbor. The hop count to
the neighbor is set to one.
Each time a route is used to forward a data packet, its Active Route (i) higher than the destination sequence number in the route
Lifetime field of both the destination and the next hop on the path table, or
to the destination is updated to be no less than the current time
plus ACTIVE_ROUTE_TIMEOUT. Since the route between each originator
and destination pair are expected to be symmetric, the Active Route
Lifetime for the previous hop, along the reverse path back to the
IP source, is also updated to be no less than the current time plus
ACTIVE_ROUTE_TIMEOUT.
6.3. Generating Route Requests (ii) the sequence numbers are equal, but the hop count (of
the new information) plus one, is smaller than the
existing hop count in the routing table, or
A node broadcasts a RREQ when it determines that it needs a route (iiI) the sequence number is unknown.
to a destination and does not have one available. This can happen
if the destination is previously unknown to the node, or if a The Lifetime field of the routing table entry is either
previously valid route to the destination expires or is broken determined from the control packet, or it is initialized to
(i.e., an infinite metric is associated with the route). The ACTIVE_ROUTE_TIMEOUT. This route may now be used to send any queued
data packets and fufills any outstanding route requests.
Each time a route is used to forward a data packet, its Active
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
current time plus ACTIVE_ROUTE_TIMEOUT. Since the route between each
originator and destination pair are expected to be symmetric, the
Active Route Lifetime for the previous hop, along the reverse path
back to the IP source, is also updated to be no less than the current
time plus ACTIVE_ROUTE_TIMEOUT.
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
packets on this route. These precursors will receive notifications
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
neighboring nodes to which a route reply was generated or forwarded.
5.3. Generating Route Requests
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
the destination is previously unknown to the node, or if a previously
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, a sequence number of zero is used. The no sequence number is known, the unknown sequence number flag MUST
Originator Sequence Number in the RREQ message is the node's own be set. The Originator Sequence Number in the RREQ message is the
sequence number. The RREQ ID field is incremented by one from the node's own sequence number, which is incremented prior to insertion
last RREQ ID used by the current node. Each node maintains only one in a RREQ. The RREQ ID field is incremented by one from the last RREQ
RREQ ID. The Hop Count field is set to zero. ID used by the current node. Each node maintains only one RREQ ID.
The Hop Count field is set to zero.
Before broadcasting the RREQ, the originating node buffers the RREQ Before broadcasting the RREQ, the originating node buffers the RREQ
ID and the Originator IP address (its own address) of the RREQ ID and the Originator IP address (its own address) of the RREQ for
for PATH_TRAVERSAL_TIME milliseconds. In this way, when the node PATH_DISCOVERY_TIME. In this way, when the node receives the packet
receives the packet again from its neighbors, it will not reprocess again from its neighbors, it will not reprocess and re-forward the
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 6.6) for delivery to the originating node SHOULD be in section 5.6) 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 6.6.3 for details about actions taken by the flag. See section 5.6.3 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.
After broadcasting a RREQ, a node waits for a RREP. If the RREP is A node SHOULD NOT generate more than RREQ_RATELIMIT RREQ messages
not received within NET_TRAVERSAL_TIME milliseconds, the node MAY try per second. After broadcasting a RREQ, a node waits for a RREP (or
again to discover a route by broadcasting a RREQ, up to a maximum other control message with current information regarding a route to
of RREQ_RETRIES times. Each new attempt MUST increment the RREQ ID the appropriate destination). If a route is not received within
field. NET_TRAVERSAL_TIME milliseconds, the node MAY try again to discover a
route by broadcasting another RREQ, up to a maximum of RREQ_RETRIES
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
is set according to the mechanism specified in section 5.4, in order
to enable control over how far the RREQ is disseminated for the each
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 without receiving any RREP, all data packets RREQ_RETRIES times at the maximum TTL without receiving any RREP, all
destined for the corresponding destination SHOULD be dropped from data packets destined for the corresponding destination SHOULD be
the buffer and a Destination Unreachable message delivered to the dropped from the buffer and a Destination Unreachable message SHOULD
application. be delivered to the application.
6.4. Controlling Dissemination of Route Request Messages 5.4. 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 as originating node SHOULD use an expanding ring search technique. In
an optimization. In an expanding ring search, the originating an expanding ring search, the originating node initially uses a TTL
node initially uses a TTL = TTL_START in the RREQ packet IP = TTL_START in the RREQ packet IP header and sets the timeout for
header and sets the timeout for receiving a RREP to 2 * TTL * receiving a RREP to NET_TRAVERSAL_TIME milliseconds. If the RREQ
NODE_TRAVERSAL_TIME milliseconds. If the RREQ times out without a times out without a corresponding RREP, the originator broadcasts the
corresponding RREP, the originator broadcasts the RREQ again with the RREQ again with the TTL incremented by TTL_INCREMENT. This continues
TTL incremented by TTL_INCREMENT. This continues until the TTL set until the TTL set in the RREQ reaches TTL_THRESHOLD, beyond which a
in the RREQ reaches TTL_THRESHOLD, beyond which a TTL = NET_DIAMETER TTL = NET_DIAMETER is used for each attempt. Each time, the timeout
is used for each attempt. Each time, the timeout for receiving a for receiving a RREP is calculated as described in Section 5.4. When
RREP is calculated as before. Each attempt increments the RREQ ID it is desired to have all retries traverse the entire ad hoc network,
field in the RREQ packet. The RREQ can be broadcast with TTL = this can be achieved by configuring TTL_START and TTL_INCREMENT both
NET_DIAMETER up to a maximum of RREQ_RETRIES times. to be the same value as NET_DIAMETER.
When a RREP is received, the Hop Count indicated in the RREP packet The Hop Count stored in an invalid routing table entry indicates
is stored as the Last Hop Count in the routing table. When a new the last known hop count to that destination in the routing table.
route to the same destination is required at a later time (e.g., upon When a new route to the same destination is required at a later time
route loss), the TTL in the RREQ IP header is initially set to this (e.g., upon route loss), the TTL in the RREQ IP header is initially
Last Hop Count plus TTL_INCREMENT. Thereafter, following each timeout set to the Hop Count plus TTL_INCREMENT. Thereafter, following
the TTL is incremented by TTL_INCREMENT until TTL = TTL_THRESHOLD is each timeout the TTL is incremented by TTL_INCREMENT until TTL =
reached. Beyond this TTL = NET_DIAMETER is used as before. TTL_THRESHOLD is reached. Beyond this TTL = NET_DIAMETER is used.
Timeouts MAY be more accurately determined dynamically via Timeouts MAY be more accurately determined dynamically via
measurement, instead of using a statically configured value related measurement, instead of using a statically configured value related
to NODE_TRAVERSAL_TIME. To accomplish this, the RREQ may carry the to NODE_TRAVERSAL_TIME.
timestamp via an extension field as defined in Section 9.2 to be
carried back by the RREP packet (again via an extension field). The
difference between the current time and this timestamp determines the
route discovery latency. The timeout may be set to be a small factor
times the average of the last few route discovery latencies for the
concerned destination. These latencies may be recorded as additional
fields in the routing table.
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 6.11). Otherwise, the (current_time + DELETE_PERIOD) (see section 5.11). Otherwise, the
soft state corresponding to the route (e.g., Last Hop Count) will be soft state corresponding to the route (e.g., last known hop count)
lost. Furthermore, a longer routing table entry expunge time MAY be will be lost. Furthermore, a longer routing table entry expunge time
configured. Any routing table entry waiting for a RREP SHOULD NOT be MAY be configured. Any routing table entry waiting for a RREP SHOULD
expunged before (current_time + PATH_TRAVERSAL_TIME). NOT be expunged before (current_time + 2 * NET_TRAVERSAL_TIME).
6.5. Processing and Forwarding Route Requests
When a node receives a RREQ, it first checks to determine whether it
has received a RREQ with the same Originator IP Address and RREQ ID
within at least the last PATH_TRAVERSAL_TIME milliseconds. If such a
RREQ has been received, the node silently discards the newly received
RREQ. The rest of this subsection describes actions taken for RREQs
that are not discarded.
The node always creates a reverse route to the Originator IP Address 5.5. Processing and Forwarding Route Requests
in its routing table if one does not already exist. If a route to
the Originator IP Address already exists, it is updated only if
either
(i) the Originator Sequence Number in the RREQ is higher When a node receives a RREQ, it first creates or updates a route to
than the destination sequence number of the Originator the previous hop without a valid sequence number (see section 5.2)
IP Address in the route table, or then checks to determine whether it has received a RREQ with
(ii) the sequence numbers are equal, but the hop count as the same Originator IP Address and RREQ ID within at least the
specified by the RREQ, plus one, is now smaller than the last PATH_DISCOVERY_TIME. If such a RREQ has been received, the
existing hop count in the routing table. node silently discards the newly received RREQ. The rest of this
subsection describes actions taken for RREQs that are not discarded.
This reverse route will be needed if the node receives a RREP back First, it first increments the hop count value in the RREQ by one,
to the node that originated the RREQ (identified by the Originator to account for the new hop through the intermediate node. Then the
IP Address). When the reverse route is created or updated, the node creates or updates a reverse route to the Originator IP Address
following actions are carried out: (see section 5.2) using the Originator Sequence Number from the RREQ
in its routing table. This reverse route will be needed if the node
receives a RREP back to the node that originated the RREQ (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 copied to the
corresponding destination sequence number in the route table corresponding destination sequence number in the route table
entry; entry and the valid sequence number field is set to true;
2. the next hop in the routing table becomes the node from which the 2. 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 3. the hop count is copied from the Hop Count in the RREQ message;
and incremented by one;
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 + PATH_TRAVERSAL_TIME - MinimalLifetime = (current time + 2*NET_TRAVERSAL_TIME -
2*HopCount*NODE_TRAVERSAL_TIME). 2*HopCount*NODE_TRAVERSAL_TIME).
The node generates a RREP (as discussed further in section 6.6) if The current node can now begin using the reverse route to forward
data packets.
The node generates a RREP (as discussed further in section 5.6) if
either: either:
(i) it is itself the destination (see section 6.6.1), or (i) it is itself the destination (see section 5.6.1), or
(ii) it has an active route to the destination, and the (ii) it has an active route to the destination, the
destination sequence number in the node's existing destination sequence number in the node's existing route
route table entry for the destination is greater than table entry for the destination is valid and greater
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). See RREQ (comparison using signed 32-bit arithmetic), and
section 6.6.2 for further information about generating the ``destination only'' ('D') flag is NOT set. See
section 5.6.2 for further information about generating
the RREP in this case. the RREP in this case.
When either of these conditions is satisfied, the node does not When either of these conditions is satisfied, the node does not
rebroadcast the RREQ. rebroadcast the RREQ.
Otherwise, if the incoming IP header has TTL larger than 1, the node 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 updates and broadcasts the RREQ to address 255.255.255.255 on all of
its configured interface(s) (see section 6.14). To update the RREQ, 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 the TTL or hop limit field in the outgoing IP header is decreased
one, and the Hop Count field in the RREQ message is incremented by by one, and the Hop Count field in the RREQ message is incremented
one, to account for the new hop through the intermediate node. 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.
6.6. Generating Route Replies 5.6. Generating Route Replies
If a node receives a route request for a destination, and either If a node receives a route request for a destination, and either
has a fresh enough route to satisfy the request or is itself the has a fresh enough route to satisfy the request or is itself the
destination, the node generates a RREP message. This node copies destination, the node generates a RREP message. This node copies
the Destination IP Address and the Originator Sequence Number in the Destination IP Address and the Originator Sequence Number in
RREQ message into the corresponding fields in the RREP message. RREQ message into the corresponding fields in the RREP message.
Processing is slightly different, depending on whether the node is Processing is slightly different, depending on whether the node is
itself the requested destination, or instead if it is an intermediate itself the requested destination, or instead if it is an intermediate
node with an admissible route to the destination. These scenarios node with an fresh enough route to the destination. These scenarios
are described in the sections below. 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.
6.6.1. Route Reply Generation by the Destination 5.6.1. Route Reply Generation by the Destination
If the generating node is the destination itself, it MUST update its If the generating node is the destination itself, it MUST increment
own sequence number to the maximum of its current sequence number and its own sequence number by one if the sequence number in the
the destination sequence number in the RREQ packet. The destination RREQ packet is equal to that incremented value. Otherwise, the
node places its sequence number into the Destination Sequence Number destination does not change its sequence number before generating
the RREP message. The destination node places its (perhaps newly
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 10) into the Lifetime field of the RREP. Each node MAY section 9) 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 10). (see section 9).
6.6.2. Route Reply Generation by an Intermediate Node 5.6.2. 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 to instead is an intermediate hop along the path from the originator
the destination, it copies its last 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 path route entry by placing The intermediate node updates the forward route entry by placing the
the last hop node (from which it received the RREQ, as indicated by last hop node (from which it received the RREQ, as indicated by the
the source IP address field in the IP header) into the precursor source IP address field in the IP header) into the precursor list for
list for the forward path route entry -- i.e., the entry for the the forward route entry -- i.e., the entry for the Destination IP
Destination IP Address. The intermediate node also updates its route Address. The intermediate node also updates its route table entry
table entry for the node originating the RREQ by placing the next hop for the node originating the RREQ by placing the next hop towards
towards the destination in the precursor list for the reverse route the destination in the precursor list for the reverse route entry
entry -- i.e., the entry for the Originator IP Address field of the -- i.e., the entry for the Originator IP Address field of the RREQ
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) in destination (indicated by the hop count in the routing table) Count
the Hop Count field in the RREP. The Lifetime field of the RREP is field in the RREP. The Lifetime field of the RREP is calculated by
calculated by subtracting the current time from the expiration time subtracting the current time from the expiration time in its route
in its route table entry. table entry.
6.6.3. Generating Gratuitous RREPs 5.6.3. 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 intermediate nodes reply to every transmission of a
given RREQ, the destination does not receive any copies of it. In given RREQ, the destination does not receive any copies of it. In
this situation, it does not learn of a route to the originating node. this situation, the destination does not learn of a route to the
This could cause the destination to initiate a network-wide route originating node. This could cause the destination to initiate a
discovery (for example, if the originator is attempting to establish route discovery (for example, if the originator is attempting to
a TCP session). In order that the destination learn of routes to the establish a TCP session). In order that the destination learn of
originating node, the originating node SHOULD set the ``gratuitous routes to the originating node, the originating node SHOULD set
RREP'' ('G') flag in the RREQ if for any reason the destination is the ``gratuitous RREP'' ('G') flag in the RREQ if for any reason
likely to need a route to the originating node. If, in response to a the destination is likely to need a route to the originating node.
RREQ with the 'G' flag set, an intermediate node returns a RREP, it If, in response to a RREQ with the 'G' flag set, an intermediate
MUST also unicast a gratuitous RREP to the destination node. 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 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 as before. The gratuitous RREP that is to be sent to the desired
destination contains the following values in the RREP message fields: 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
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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 in
response to that (fictitious) RREQ. response to that (fictitious) RREQ.
6.7. Receiving and Forwarding Route Replies 5.7. Receiving and Forwarding Route Replies
When a node receives a RREP message, it compares the Destination When a node receives a RREP message, it first creates or updates
Sequence Number in the message with its own copy of destination a route to the previous hop without a valid sequence number (see
sequence number for the Destination IP Address in the RREP message. section 5.2) then increments the hop count value in the RREP by one,
The forward route for this destination is created if it does not to account for the new hop through the intermediate node. Call this
already exist, or it is updated only if (i) the Destination Sequence incremented value the "New Hop Count". Then the forward route for
Number in the RREP is greater than the node's copy of the destination this destination is created if it does not already exist. Otherwise,
sequence number, or (ii) the sequence numbers are the same, but the the node compares the Destination Sequence Number in the message with
route is no longer active, or (iii) the sequence numbers are the its own stored destination sequence number for the Destination IP
same, and the Hop Count in the RREP is smaller than the hop count Address in the RREP message. Upon comparison, the existing entry is
in route table entry. In either of these cases, the next hop in updated only if either
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 (i) the sequence number in the routing table is invalid in
IP header; the hop count is the Hop Count in the RREP message plus route table entry.
one; the expiry time is the current time plus the Lifetime in the
RREP message; and the destination sequence number is the Destination (ii) the Destination Sequence Number in the RREP is greater
than the node's copy of the destination sequence number
and the known value is valid, or
(iii) the sequence numbers are the same, but the route is no
longer active, or
(iiii) the sequence numbers are the same, and the New Hop Count
is smaller than the hop count in route table entry.
If either the route table entry to the destination is created or
updated, 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 the New Hop Count;
the expiry time is the current time plus the Lifetime in the RREP
message; and the destination sequence number is the Destination
Sequence Number in the RREP message. The current node can now begin Sequence Number in the RREP message. The current node can now begin
using this route to forward data packets to the destination. using 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 the route table entry. 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
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
back (see section 5.8).
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)). ACTIVE_ROUTE_TIMEOUT)). Finally, the precursor list for the next hop
towards the destination is updated to contain the next hop towards
If a node forwards a RREP over a link that is likely to have errors the source.
or be unidirectional, 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 back (see section 6.8).
6.8. Operation over Unidirectional Links 5.8. 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 network-wide route discovery after a originator will reattempt route discovery after a timeout (see
timeout (see section 6.3). However, the same scenario might well section 5.3). However, the same scenario might well be repeated, and
be repeated, and no route would be discovered even after repeated no route would be discovered even after repeated retries. Unless
retries. Unless corrective action is taken, this can happen even corrective action is taken, this can happen even when bidirectional
when bidirectional routes between originator and destination do routes between originator and destination do exist. Link layers
exist. Link layers using broadcast transmissions for the RREQ will using broadcast transmissions for the RREQ will not be able to detect
not be able to detect the presence of such unidirectional links. In the presence of such unidirectional links. In AODV, any node acts on
AODV, any node acts on only the first RREQ with the same RREQ ID only the first RREQ with the same RREQ ID and ignores any subsequent
and ignores any subsequent RREQs. Suppose, for example, that the RREQs. Suppose, for example, that the first RREQ arrives along a
first RREQ arrives along a path that has one or more unidirectional path that has one or more unidirectional link(s). A subsequent RREQ
link(s). A subsequent RREQ may arrive via a bidirectional path may arrive via a bidirectional path (assuming such paths exist), but
(assuming such paths exist), but it will be ignored. 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 10). This period should be set BLACKLIST_TIMEOUT period (see section 9). 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 6.3. of route request retry attempts as described in section 5.3.
6.9. Hello Messages 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
received will likely come just after the time when the RREP was sent
with the 'A' bit. This information is expected to be sufficient
to provide assurance to the sender of the RREP that the link is
currently bidirectional. However, that assurance cannot be always
expected to remain permanently.
A node MAY offer connectivity information by broadcasting local 5.9. Hello Messages
Hello messages as follows. Every HELLO_INTERVAL milliseconds, the
node checks whether it has sent a broadcast (e.g., a RREQ or an A node MAY offer connectivity information by broadcasting local Hello
appropriate layer 2 message) within the last HELLO_INTERVAL. If messages. A node SHOULD only use hello messages if it is part of an
it has not, it MAY broadcast a RREP with TTL = 1, called a Hello active route. Every HELLO_INTERVAL milliseconds, the node checks
message, with the RREP message fields set as follows: 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
broadcast a RREP with TTL = 1, called a Hello message, with the RREP
message fields set as follows:
Destination IP Address Destination IP Address
The node's IP address. The node's IP address.
Destination Sequence Number Destination Sequence Number
The node's latest sequence number. The node's latest sequence number.
Hop Count 0 Hop Count 0
Lifetime ALLOWED_HELLO_LOSS * HELLO_INTERVAL Lifetime ALLOWED_HELLO_LOSS * HELLO_INTERVAL
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Destination IP Address Destination IP Address
The node's IP address. The node's IP address.
Destination Sequence Number Destination Sequence Number
The node's latest sequence number. The node's latest sequence number.
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 broken. When this assume that the link to this neighbor is currently lost. When this
happens, the node SHOULD proceed as in Section 6.11. happens, the node SHOULD proceed as in Section 5.11.
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. Routes that are newly Sequence Number from the Hello message. The current node can now
created from the reception of Hello messages might have empty begin using this route to forward data packets. Routes that are
precursor lists, and in that case would not trigger RERR messages created by hello messages and not used by any other active routes
when the neighbor moves away and the neighbor route expires. will have empty precursor lists and would not trigger a RERR message
when the neighbor moves away and a neighbor timeout occurs.
6.10. Maintaining Local Connectivity 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
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.
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* 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 broken, and take the forwarding node SHOULD assume that the link is lost, and take
corrective action by following the methods specified in Section 6.11. corrective action by following the methods specified in Section 5.11.
6.11. Route Error Messages, Route Expiry and Route Deletion 5.11. Route Error Messages, Route Expiry and Route Deletion
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 to inappropriate). Even when the RERR message is iteratively unicast
several precursors, it is considered to be a single control message to several precursors, it is considered to be a single control
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
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, or if the routing table route in its routing table while transmitting data, or
entry for the next hop expires (also see section 6.1),
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 has already made an does not have an active route and is not repairing (if
attempt at local repair (if local repair is being used), using local repair), or
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 in the local routing table that use the unreachable
neighbor as the next hop. For case (ii), there is only one neighbor as the next hop. For case (ii), there is only one
unreachable destination, which is the destination of the data packet unreachable destination, which is the destination of the data packet
that cannot be delivered. For case (iii), the list should consist of that cannot be delivered. For case (iii), the list should consist of
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received RERR as the next hop. 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 one destination(s) in the newly created RERR. In case there is only
unique neighbor that needs to receive the RERR, the RERR SHOULD be one unique neighbor that needs to receive the RERR, the RERR
unicast to that destination. Otherwise the RERR is typically sent SHOULD be unicast toward that destination. Otherwise the RERR is
to the local broadcast address (Destination IP == 255.255.255.255, typically sent to the local broadcast address (Destination IP ==
TTL == 1) with the unreachable destinations, and their corresponding 255.255.255.255, TTL == 1) with the unreachable destinations, and
destination sequence numbers, included in the packet. The DestCount their corresponding destination sequence numbers, included in the
field of the RERR packet indicates the number of unreachable packet. The DestCount field of the RERR packet indicates the number
destinations included in the packet. of unreachable 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 entry is invalidated by copying the Hop Count to the Last Hop 1. The destination sequence number of this routing entry, if it
Count field and then making the Hop Count infinity. exists and is valid, is incremented for cases (i) and (ii) above,
and copied from the incoming RERR in case (iii) above.
2. The destination sequence number of this routing entry, if it 2. The entry is invalidated by marking the route entry as invalid
exists, is incremented by one for cases (i) and (ii) above, and
copied from the incoming RERR in case (iii) above.
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 MUST 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 10. Section 9.
6.12. Local Repair 5.12. 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 to originator) + max(MIN_REPAIR_TTL, 0.5 * #hops) + LOCAL_ADD_TTL,
LOCAL_ADD_TTL.
Thus, local repair attempts should never be visible to the where #hops is the number of hops to the sender (originator) of the
originating node, and will always have TTL >= MIN_REPAIR_TTL currently undeliverable packet. Thus, local repair attempts will
+ LOCAL_ADD_TTL. The node initiating the repair then waits the often be invisible to the originating node, and will always have TTL
discovery period to receive RREPs in response to the RREQ. If, at >= MIN_REPAIR_TTL + LOCAL_ADD_TTL. The node initiating the repair
the end of the discovery period, it has not received a RREP for that then waits the discovery period to receive RREPs in response to the
destination, it proceeds as described in Section 6.11 by transmitting RREQ. During local repair data packets SHOULD be buffered. If, at
a RERR message for that destination. the end of the discovery period, it has not received a RREP (or other
control message creating or updating the route) for that destination,
it proceeds as described in Section 5.11 by transmitting a RERR
message for that destination.
On the other hand, if the node receives one or more RREPs during the On the other hand, if the node receives one or more RREPs (or
discovery period, it proceeds as described in Section 6.7, updating other control message creating or updating the route to the desired
its route table entry for that destination. It then compares the hop destination) during the discovery period, it first compares the hop
count of the new route with the value in the last hop count route count of the new route with the value in the hop count field of the
table entry for that destination. If the hop count of the newly invalid route table entry for that destination. If the hop count of
determined route to the destination is greater than the hop count of the newly determined route to the destination is greater than the
the previously known route, as recorded in the last hop count field, hop count of the previously known route the node SHOULD issue a RERR
the node SHOULD create a RERR message for the destination, with the message for the destination, with the 'N' bit set. Then it proceeds
'N' bit set. as described in Section 5.7, updating its route table entry for that
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 6.3. described in Section 5.3.
Local repair of link breaks in active routes sometimes results in Local repair of link breaks in routes sometimes results in increased
increased path lengths to those destinations. Repairing the link path lengths to those destinations. Repairing the link locally is
locally is likely to increase the number of data packets that are likely to increase the number of data packets that are able to be
able to be delivered to the destinations, since data packets will not delivered to the destinations, since data packets will not be dropped
be dropped as the RERR travels to the originating node. Sending a as the RERR travels to the originating node. Sending a RERR to the
RERR to the originating node after locally repairing the link break originating node after locally repairing the link break may allow the
may allow the originator to find a fresh route to the destination originator to find a fresh route to the destination that is better,
that is better, based on current node positions. However, it based on current node positions. However, it does not require the
does not require the originating node to rebuild the route, as the originating node to rebuild the route, as the originator may be done,
originator may be done, or nearly done, with the data session. or nearly done, with the data session.
When a link breaks along an active route, there are often multiple When a link breaks along an active route, there are often multiple
destinations that become unreachable. The node that is upstream of destinations that become unreachable. The node that is upstream
the broken link tries an immediate local repair for only the one of the lost link tries an immediate local repair for only the one
destination towards which the data packet was traveling. Other destination towards which the data packet was traveling. Other
routes using the same link MUST be marked as broken, but the node routes using the same link MUST be marked as invalid, but the node
handling the local repair MAY flag each such newly broken route as handling the local repair MAY flag each such newly lost route as
locally repairable; this local repair flag in the route table MUST be locally repairable; this local repair flag in the route table MUST be
reset when the route times out (e.g., after the route has been not reset when the route times out (e.g., after the route has been not
been active for ACTIVE_ROUTE_TIMEOUT). Before the timeout occurs, been active for ACTIVE_ROUTE_TIMEOUT). Before the timeout occurs,
these other routes will be repaired as needed when packets arrive these other routes will be repaired as needed when packets arrive
for the other destinations. Alternatively, depending upon local for the other destinations. Alternatively, depending upon local
congestion, the node MAY begin the process of establishing local congestion, the node MAY begin the process of establishing local
repairs for the other routes, without waiting for new packets to repairs for the other routes, without waiting for new packets to
arrive. arrive.
6.13. Actions After Reboot 5.13. 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 next
hop. This can potentially create routing loops. To prevent this hop. This can potentially create routing loops. To prevent this
possibility, each node on reboot waits for DELETE_PERIOD. During possibility, each node on reboot waits for DELETE_PERIOD. During this
this time, the node does not transmit any RREP messages. If the time, the node does not transmit any RREP messages. If the node
node receives a RREQ, RREP, or RERR control packet, it SHOULD create receives a RREQ, RREP, or RERR control packet, it SHOULD create route
route entries as appropriate given the sequence number information entries as appropriate given the sequence number information in the
in the control packets. If the node receives a data packet for control packets, but MUST not forward any control packets. If the
some other destination, it MUST broadcast a RERR as described in node receives a data packet for some other destination, it SHOULD
subsection 6.11 and reset the waiting timer to expire after current broadcast a RERR as described in subsection 5.11 and MUST reset the
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 [1] that by the time the rebooted node comes out of
the waiting phase and becomes an active router again, none of its the waiting phase and becomes an active router again, none of its
neighbors will be using it as an active next hop any more. Its own neighbors will be using it as an active next hop any more. Its own
sequence number gets updated once it receives a RREQ from any other sequence number gets updated once it receives a RREQ from any other
node, as the RREQ always carries the maximum destination sequence node, as the RREQ always carries the maximum destination sequence
number seen en route. number seen en route.
6.14. Interfaces 5.14. 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 multi-homed radios, the interface over which packets arrive must
be known to AODV whenever a packet is received. This includes the be known to AODV whenever a packet is received. This includes the
reception of RREQ, RREP, and RERR messages. Whenever a packet is reception of RREQ, RREP, and RERR messages. Whenever a packet is
received from a new neighbor, the interface on which that packet was received from a new neighbor, the interface on which that packet was
received is recorded into the route table entry for that neighbor, received is recorded into the route table entry for that neighbor,
along with all the other appropriate routing information. Similarly, along with all the other appropriate routing information. Similarly,
whenever a route to a new destination is learned, the interface whenever a route to a new destination is learned, the interface
through which the destination can be reached is also recorded into through which the destination can be reached is also recorded into
the destination's route table entry. 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 brodacast 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 precursor nodes
for that route. for that route.
7. AODV and Aggregated Networks 6. 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 leader.
8. Using AODV with Other Networks If several nodes in the subnet advertise reachability to the subnet
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
advertising reachability.
The behavior of default routes (i.e., routes with routing prefix
length 0) is not defined in this specification. Selection of routes
sharing prefix bits should be according to longest match first.
7. 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 7) for any relevant networks within the external routers (see Section 6) 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.
9. Extensions 8. Extensions
RREQ and RREP messages have extensions defined in the following In this section, the format of extensions to the RREQ and RREP
format: messages is specified. All such extensions appear after the message
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 ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where: where:
Type 1 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. 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.
9.1. Hello Interval Extension Format 8.1. 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 2
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 6.9). section 5.9).
9.2. Timestamp Extension Format
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ Timestamp in NTP Format +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type 3
Length 8
Timestamp
The number of seconds and fractional seconds since the
Timestamp Extension was added to the control message as
transmitted by the originator (e.g., of a RREQ message).
The Timestamp value is structured according to the format for NTP
timestamps specified in RFC 2030 [5]. For convenience, the following
text is taken from that document, but should not be used as a
substitute for consulting RFC 2030 for details.
NTP timestamps are represented as a 64-bit unsigned fixed-point
number, in seconds relative to 0h on 1 January 1900. The integer
part is in the first 32 bits and the fraction part in the last 32
bits. In the fraction part, the non-significant low order can be
set to 0. It is advisable to fill the non-significant low order
bits of the timestamp with a random, unbiased bitstring, both to
avoid systematic roundoff errors and as a means of loop detection and
replay detection (see below). One way of doing this is to generate a
random bitstring in a 64-bit word, then perform an arithmetic right
shift a number of bits equal to the number of significant bits of the
timestamp, then add the result to the original timestamp.
10. Configuration Parameters 9. 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 associated with AODV protocol operations. A particular mobile node
node may wish to change certain of the parameters, in particular may wish to change certain of the parameters, in particular the
the NET_DIAMETER, NODE_TRAVERSAL_TIME, MY_ROUTE_TIMEOUT, NET_DIAMETER, MY_ROUTE_TIMEOUT, ALLOWED_HELLO_LOSS, RREQ_RETRIES,
ALLOWED_HELLO_LOSS, RREQ_RETRIES, and possibly the HELLO_INTERVAL. In and possibly the HELLO_INTERVAL. In the latter case, the node
the latter case, the node should advertise the HELLO_INTERVAL in its should advertise the HELLO_INTERVAL in its Hello messages, by
Hello messages, by appending a Hello Interval Extension to the RREP appending a Hello Interval Extension to the RREP message. Choice
message. Choice of these parameters may affect the performance of of these parameters may affect the performance of the protocol.
the protocol. The configured value for MY_ROUTE_TIMEOUT MUST be at Changing NODE_TRAVERSAL_TIME also changes the node's estimate
least 2 * REV_ROUTE_LIFE. of the NET_TRAVERSAL_TIME, and so can only be done with suitable
knowledge about the behavior of other nodes in the ad hoc network.
The configured value for MY_ROUTE_TIMEOUT MUST be at least 2 *
PATH_DISCOVERY_TIME.
Parameter Name Value Parameter Name Value
---------------------- ----- ---------------------- -----
ACTIVE_ROUTE_TIMEOUT 3,000 Milliseconds ACTIVE_ROUTE_TIMEOUT 3,000 Milliseconds
ALLOWED_HELLO_LOSS 2 ALLOWED_HELLO_LOSS 2
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
NEXT_HOP_WAIT NODE_TRAVERSAL_TIME + 10 NEXT_HOP_WAIT NODE_TRAVERSAL_TIME + 10
NODE_TRAVERSAL_TIME 40 NODE_TRAVERSAL_TIME 40
NET_TRAVERSAL_TIME 3 * NODE_TRAVERSAL_TIME * NET_DIAMETER / 2 NET_TRAVERSAL_TIME 2 * NODE_TRAVERSAL_TIME * NET_DIAMETER
PATH_DISCOVERY_TIME 2 * NET_TRAVERSAL_TIME2RREQ_RETRIES PATH_DISCOVERY_TIME 2 * NET_TRAVERSAL_TIME
RERR_RATELIMIT 10
RREQ_RETRIES 2
RREQ_RATELIMIT 10
TTL_START 1 TTL_START 1
TTL_INCREMENT 2 TTL_INCREMENT 2
TTL_THRESHOLD 7 TTL_THRESHOLD 7
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).
DELETE_PERIOD should be an upper bound on the time for which an DELETE_PERIOD should be an upper bound on the time for which an
skipping to change at page 27, line 11 skipping to change at page 28, line 30
of K subsequent Hello messages from a neighbor if the link is of K subsequent Hello messages from a neighbor if the link is
working and the neighbor is sending no other traffic. Covering all working and the neighbor is sending no other traffic. Covering all
possibilities, possibilities,
DELETE_PERIOD = K * max (ACTIVE_ROUTE_TIMEOUT, HELLO_INTERVAL) (K = 5 is DELETE_PERIOD = K * max (ACTIVE_ROUTE_TIMEOUT, HELLO_INTERVAL) (K = 5 is
recommended). 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 queueing 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 [4] 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. This [(TTL_THRESHOLD - TTL_START)/TTL_INCREMENT] + 1 + RREQ_RETRIES *
is to account for possible additional route discovery attempts. NET_TRAVERSAL_TIME. This is to account for possible additional route
discovery attempts.
11. Security Considerations 10. 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. If there is danger of such attacks, AODV control messages
must be protected by use of authentication techniques, such as those must be protected by use of authentication techniques, such as those
involving generation of unforgeable and cryptographically strong involving generation of unforgeable and cryptographically strong
message digests or digital signatures. In particular, RREP messages message digests or digital signatures. In particular, RREP messages
SHOULD be authenticated to avoid creation of spurious routes to a SHOULD be authenticated to avoid creation of spurious routes to a
desired destination. Otherwise, an attacker could masquerade as the desired destination. Otherwise, an attacker could masquerade as the
desired destination, and maliciously deny service to the destination desired destination, and maliciously deny service to the destination
skipping to change at page 28, line 5 skipping to change at page 29, line 20
Since AODV does not make any assumption about the nature of the Since AODV does not make any assumption about the nature of the
address assignment to the mobile nodes except that they are presumed address assignment to the mobile nodes except that they are presumed
to have unique IP addresses, no definite statements can be made about to have unique IP addresses, no definite statements can be made about
the applicability of IPsec authentication headers or key exchange the applicability of IPsec authentication headers or key exchange
mechanisms. However, if the mobile nodes in the ad hoc network have mechanisms. However, if the mobile nodes in the ad hoc network have
pre-established security associations, they should be able to use the pre-established security associations, they should be able to use the
same authentication mechanisms based on their IP addresses as they same authentication mechanisms based on their IP addresses as they
would have used otherwise. would have used otherwise.
11. IPv6 Considerations
See [6] for detailed operation for IPv6. The only changes to the
protocol are that the address fields are enlarged.
12. Acknowledgments 12. Acknowledgments
Special thanks to Ian Chakeres, UCSB, for his extensive suggestions
and contributions to this revision.
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 6.11), Yves Prelot, Manel Nordstrom (who provided text for section 5.11), Yves Prelot, Marc
Guerrero Zapata, Philippe Jacquet, Ian Chakeres, and Fred Baker. Mosko, Manel Guerrero Zapata, Philippe Jacquet, and Fred Baker.
References References
[1] Karthikeyan Bhargavan, Carl A. Gunter, and Davor Obradovic. [1] Karthikeyan Bhargavan, Carl A. Gunter, and Davor Obradovic.
Fault Origin Adjudication. In Proceedings of the Workshop on Fault Origin Adjudication. In Proceedings of the Workshop on
Formal Methods in Software Practice, Portland, OR, August 2000. Formal Methods in Software Practice, Portland, OR, August 2000.
[2] S. Bradner. Key words for use in RFCs to Indicate Requirement [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.
skipping to change at page 29, line 5 skipping to change at page 30, line 21
[4] IEEE 802.11 Committee, AlphaGraphics #35, 10201 N.35th Avenue, [4] 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 [5] D. Mills. Simple Network Time Protocol (SNTP) Version 4 for
IPv4, IPv6 and OSI. Request for Comments (Informational) 2030, IPv4, IPv6 and OSI. Request for Comments (Informational) 2030,
Internet Engineering Task Force, October 1996. Internet Engineering Task Force, October 1996.
[6] C. Perkins, E. Royer, and S. Das. Ad Hoc On Demand Distance
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 (10) of the AODV The following are major changes between this version (11) of the AODV
draft and the previous version (09): draft and the previous version:
- Specified that the next hop towards the originator of a RREQ - Added definitions for valid route, invalid route and sequence
must be added to the precursor list for the destination, when an number.
intermediate node sends a Gratuitous RREP to the next hop towards
that destination (see section 6.6.3).
- Specified that sequence numbers are to be compared as signed - Re-added discussion in processing and forwarding RREQ that it is
integers. necessary to update the destination sequence number in a RREQ
being forwarded to the maximum known sequence number.
- Clarified that "broadcast" means transmission to 255.255.255.255, - Added ``destination only'' ('D') flag.
and replaced terminology about "flooding" by "network-wide route
discovery", since that is what AODV does.
- In line with last point, replaced "Flooding ID" by "RREQ ID", and - Specify hello messages should only be used by nodes on active
FLOOD_RECORD_TIME by RREQ_RECORD_TIME. routes.
- Changed name of "Source IP Address" field to be "Originator - Clarify RERR messages are generated only in response failing to
IP Address" in RREQ message format, and changed the ``Source send data.
Sequence Number'' field to be the ``Originator Sequence Number''
field in the RREQ and RREP message formats.
- Clarified that RREQ messages do not have to be rebroadcast over - Removed term ``broken''.
some types of network interfaces, when it may be presumed that
all nodes reachable from the network interface have already
received the same incoming RREQ message as the node processing
the RREQ (see section 6.14).
- Made section 4-7 in version 09 subsections of one section in - Routes should be created or updated to the previous hop when a
version 10. control message is received.
- Changed the Lifetime field in section 6.2 to be set to - Added comments near route creation instructions that routes may
HELLO_INTERVAL * ALLOWED_HELLO_LOSS on reception of a control be used once created and should cancel further route discovery or
packet. local repair for those destinations.
- Added that the lifetime for the route to the next hop towards a - Removed NTP timestamp extension
destination should be updated when a data packet is forwarded to
that node.
- Updated the calculation of MinimalLifetime in section 6.5. - Added ``route state'' field to routing table.
- Clarified section 6.11. - Removed ``last hop count'' field from routing table.
- Added a definition for the timestamp extension field. - Removed ``infinite hop count'' from draft.
- Introduced a new parameter, PATH_DISCOVERY_TIME, to replace the - Added ``unknown sequence number'' flag to RREQ.
former RREQ_RECORD_TIME, REV_ROUTE_LIFE, and RREP_WAIT_TIME
parameters. - Restructured Route Table Entries and Precursor Lists (section 5.2
to inlcude how to create and update routes.
- Route Lifetime to source must be updated when forwarding data
packets.
- Specify that during reboot no control messages should be
forwarded.
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
USA USA
+1 650 625 2986 +1 650 625 2986
+1 650 691 2170 (fax) +1 650 691 2170 (fax)
charliep@iprg.nokia.com charliep@iprg.nokia.com
Elizabeth M. Belding-Royer Elizabeth M. Belding-Royer
Dept. of Computer Science Department of Computer Science
University of California, Santa Barbara University of California, Santa Barbara
Santa Barbara, CA 93106 Santa Barbara, CA 93106
+1 805 893 3411 +1 805 893 3411
+1 805 893 8553 (fax) +1 805 893 8553 (fax)
ebelding@cs.ucsb.edu ebelding@cs.ucsb.edu
Samir R. Das Samir R. Das
Department of Electrical and Computer Engineering Department of Electrical and Computer Engineering
& Computer Science & Computer Science
University of Cincinnati University of Cincinnati
 End of changes. 

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