draft-ietf-manet-aodv-00.txt   draft-ietf-manet-aodv-01.txt 
Mobile Ad Hoc Networking Working Group Charles Perkins Mobile Ad Hoc Networking Working Group Charles Perkins
INTERNET DRAFT Sun Microsystems INTERNET DRAFT Sun Microsystems
20 November 1997 10 August 1998 Elizabeth M. Royer
University of California, Santa Barbara
Ad Hoc On Demand Distance Vector (AODV) Routing Ad Hoc On Demand Distance Vector (AODV) Routing
draft-ietf-manet-aodv-00.txt draft-ietf-manet-aodv-01.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
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Abstract Abstract
The Ad Hoc On-Demand Distance Vector (AODV) routing protocol is The Ad Hoc On-Demand Distance Vector (AODV) routing protocol is
intended for use by mobile nodes in an ad hoc network characterized intended for use by mobile nodes in an ad hoc network characterized
by frequent changes in link connectivity to each other caused by frequent changes in link connectivity to each other caused
by relative movement. It offers quick adaptation to dynamic by relative movement. It offers quick adaptation to dynamic
link conditions, low processing and memory overhead, low network link conditions, low processing and memory overhead, low network
utilization, and establishment of routes between sources and utilization, and establishment of both unicast and multicast routes
destination which are loop free at all times. It makes use of between sources and destinations which are loop free at all times.
destination sequence numbers, which are a novel means of ensuring It makes use of destination sequence numbers, which are a novel means
loop freedom even in the face of anomalous delivery of routing of ensuring loop freedom even in the face of anomalous delivery
control messages, and which solve classical problems associated with of routing control messages, and which solve classical problems
distance vector protocols, including the problem of ''counting to associated with distance vector protocols, including the problem of
infinity''. "counting to infinity".
Contents Contents
Status of This Memo i Status of This Memo i
Abstract i Abstract i
1. Introduction 1 1. Introduction 2
2. Overview 2 2. Overview 2
3. AODV Terminology 3 3. AODV Terminology 4
4. Route Request Message Format 4 4. Route Request Message Format 6
5. Route Reply Message Format 5 5. Route Reply Message Format 8
6. Node Operation 5 6. Multicast Route Invalidation Message Format 10
6.1. Maintaining Route Utilization Records . . . . . . . . . . 5
6.2. Generating Route Requests . . . . . . . . . . . . . . . . 6
6.3. Forwarding Route Requests . . . . . . . . . . . . . . . . 6
6.4. Generating Route Replies . . . . . . . . . . . . . . . . 7
6.5. Generating Hello Messages . . . . . . . . . . . . . . . . 8
6.6. Initiating Triggered Route Replies . . . . . . . . . . . 8
6.7. Detecting Link Breakage . . . . . . . . . . . . . . . . . 9
7. Configuration Parameters 9 7. Node Operation - Unicast 11
7.1. Maintaining Route Utilization Records . . . . . . . . . . 11
7.2. Generating Route Requests . . . . . . . . . . . . . . . . 11
7.3. Forwarding Route Requests . . . . . . . . . . . . . . . . 12
7.4. Generating Route Replies . . . . . . . . . . . . . . . . 13
7.5. Generating Hello Messages . . . . . . . . . . . . . . . . 13
7.6. Initiating Triggered Route Replies . . . . . . . . . . . 14
7.7. Detecting Link Breakage . . . . . . . . . . . . . . . . . 15
8. Extensions 10 8. Node Operation - Multicast 15
8.1. Maintaining Multicast Tree Utilization Records . . . . . 15
8.2. Generating Multicast Route Requests . . . . . . . . . . . 15
8.3. Forwarding Multicast Route Requests . . . . . . . . . . . 17
8.4. Generating Multicast Route Replies . . . . . . . . . . . 17
8.5. Route Deletion and Multicast Tree Pruning . . . . . . . . 18
8.6. Repairing Link Breakages . . . . . . . . . . . . . . . . 20
8.7. Initiating Triggered Route Replies . . . . . . . . . . . 22
9. Security Considerations 10 9. Configuration Parameters 22
10. Extensions 24
11. Security Considerations 24
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 also defines timely responses are not in active communication. Additionally, AODV allows for the
to link breakages. The operation of AODV is loop free, and by formation of multicast groups whose membership is free to change
avoiding the Bellman-Ford "counting to infinity" problem offers quick during the lifetime of the network. AODV also defines timely
convergence when the ad-hoc network topology changes (typically, when responses to link breakages and changes in network topology. The
a node moves in the network). operation of AODV is loop free, and by avoiding the Bellman-Ford
"counting to infinity" problem offers quick convergence when the
ad-hoc network topology changes (typically, when a node moves in the
network).
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 itself for any usable route number is created by the destination or the multicast grouphead for
information it sends to requesting nodes. Using destination sequence any usable route information it sends to requesting nodes. Using
numbers ensures loop freedom, and is simple to program. Given the destination sequence numbers ensures loop freedom and is simple to
choice between two routes to a destination, a requesting node always program. Given the choice between two routes to a destination, a
selects one with the greatest sequence number. requesting node always selects the one with the greatest sequence
number.
Another feature of AODV is that link breakages cause immediate Another feature of AODV is that link breakages cause immediate
notifications to be sent to the affected set of nodes, but only that notifications to be sent to the affected set of nodes, but only that
set. set of nodes.
2. Overview 2. Overview
Route Requests (RREQs) and Route Replies (RREPs) are the two message Route Requests (RREQs), Route Replies (RREPs), and Multicast
types defined by AODV. These message types are handled by UDP, Route Invalidations (MINVs) are the three message types defined
and normal IP header processing applies. So, for instance, the by AODV. These message types are handled by UDP, and normal IP
requesting node is expected to use its IP address as the source IP header processing applies. So, for instance, the requesting node
address for the messages. The range of dissemination of broadcast is expected to use its IP address as the source IP address for the
RREQs can be indicated by the TTL in the IP header. Fragmentation is messages. The range of dissemination of broadcast RREQs can be
typically not required. indicated by the TTL in the IP header. Fragmentation is typically
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
new destination is needed, the node uses a broadcast RREQ to find a to a new destination (either a single node or a multicast group)
route to the destination. A route can be determined when the request is needed, the node uses a broadcast RREQ to find a route to the
reaches either the destination itself, or an intermediate node with a destination. A route can be determined when the request reaches
fresh enough route to the destination. The route is made available either the destination itself, or an intermediate node with a fresh
by unicasting a RREP back to the source of the RREQ. Since each node enough route to the destination. The route is made available by
unicasting a RREP back to the source of the RREQ. Since each node
receiving the request keeps track of a route back to the source of receiving the request keeps track of a route back to the source of
the request, the RREP Reply can be unicast back from the destination the request, the RREP can be unicast back from the destination to the
to the source, or from any intermediate node that is able to satisfy source, or from any intermediate node that is able to satisfy the
the request back to the source. request back to the source. In the multicast scenario, RREQs are
also used when a node wishes to join a multicast group. A special
join flag in the RREQ lets nodes know that when they receive the
RREP, they are not just setting route pointers but are actually
grafting a branch on to the multicast tree.
If a RREP is broadcast to the limited broadcast address If a RREP is broadcast to the limited broadcast address
(255.255.255.255), and has a TTL of one, and a destination address of (255.255.255.255), and has a TTL of one, and a destination address
the node itself with metric 0, then it is received by all the node's of the node itself with metric 0, then it is received by all the
neighbors, and treated by them as a "hello" message. This hello node's neighbors, and treated by them as a "hello" message. This
message is a local advertisement for the continued presence of the hello message is a local advertisement for the continued presence of
node. Neighbors that are using routes through the broadcasting node the node. Neighbors that are using routes through the broadcasting
will continue to mark the routes as valid. If hello messages from a node will continue to mark the routes as valid. If hello messages
particular node stop coming, the neighbor can assume that the node from a particular node stop coming, the neighbor can assume that the
has moved away. When that happens, the neighbor will mark the link node has moved away. When that happens, the neighbor will mark the
to the node as broken, and may trigger a notification to some of its link to the node as broken, and may trigger a notification to some of
other neighbors that the link has broken. its other neighbors that the link has broken. Hello messages also
carry multicast group and corresponding grouphead IP addresses. This
information is used for repairing multicast trees after a previously
disconnected portion of the network containing part of the multicast
tree becomes reachable once again.
Since AODV is a routing protocol, it deals with route table Since AODV is a routing protocol, it deals with route table
management. AODV assumes the following fields exist in each route management. AODV assumes the following fields exist in each route
table entry: table entry:
- Destination IP Address - Destination IP Address
- Destination Sequence Number - Destination Sequence Number
- Hop Count - Hop Count
- Next Hop - Next Hop
- Lifetime - Lifetime
This information must be kept even for ephemeral routes, such as are This information must be kept even for ephemeral routes, such as are
created to temporarily keep track of reverse paths towards nodes created to temporarily keep track of reverse paths towards nodes
originating RREQs. originating RREQs. For multicast tree routes, the Next Hop field is
likely to contain more than one entry. For multicast tree routes,
the following information is stored in each entry of the multicast
route table:
- Multicast Group IP Address
- Multicast Grouphead IP Address
- Hop Count
- Next Hops
- Lifetime
Here the Hop Count corresponds to the distance in hops to the
multicast grouphead. Also, the Next Hops field is a linked list of
structures, each of which contain the fields:
- Node IP Address
- Active Flag
The Active Flag indicates whether the link has actually been set, or
whether an MINV messages is still pending (see Section 8.5).
3. AODV Terminology 3. AODV Terminology
This section defines terminology used with AODV that is not already This section defines terminology used with AODV that is not already
defined in [2]. defined in [2].
multicast grouphead
A node which is a member of the given multicast group and which
is the first such group member in the connected portion of
the network. This node is responsible for initializing the
multicast group destination sequence number.
multicast tree
The tree containing all nodes which are members of the
multicast group and all nodes which are needed to connect the
multicast group members.
multicast route table
The table were ad-hoc nodes keep routing (including next hops)
information for various multicast groups.
request table
The table where ad-hoc nodes keep information concerning the
first node to request to join a multicast group. There is one
entry in the table for each multicast group for which the node
has received a RREQ with the J flag set (see Section 8.2.
route table route table
The table where ad-hoc nodes keep routing (including next hop) The table where ad-hoc nodes keep routing (including next hop)
information for various destinations. For IPv6, this can be information for various destinations. For IPv6, this can be
associated with the Destination Cache. associated with the Destination Cache.
triggered update triggered update
An unsolicited route update transmitted by an intermediate node An unsolicited route update transmitted by an intermediate node
along the path to the destination. along the path to the destination.
This protocol specification uses conventional meanings [1] for This protocol specification uses conventional meanings [1] for
capitalized words such as MUST, SHOULD, etc., to indicate requirement capitalized words such as MUST, SHOULD, etc., to indicate requirement
levels for various protocol features. levels for various protocol features.
4. Route Request Message Format 4. Route Request 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 | Reserved | Hop Count | | Type |J|R| Reserved | Hop Count |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Broadcast ID | | Broadcast ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Destination IP address | | Destination IP address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Destination Sequence Number | | Destination Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Source IP address | | Source IP address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Source Sequence Number | | Source Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The format of the Route Request message is illustrated above, and The format of the Route Request message is illustrated above, and
contains the following fields: contains the following fields:
Type xx Type xx
J Join flag; set when source node wants to join
multicast group.
R Repair flag; set when a node wants to initiate
a repair to connect two previously disconnected
portions of the multicast tree.
Reserved Sent as 0; ignored on reception. Reserved Sent as 0; ignored on reception.
Hop Count The number of hops from the Source IP Address to the Hop Count The number of hops from the Source IP Address to the
node handling the request. node handling the request.
Broadcast ID Broadcast ID
A sequence number identifying the particular RREQ A sequence number identifying the particular RREQ
uniquely when taken in conjunction with the source node's uniquely when taken in conjunction with the source
IP address. node's IP address.
Destination IP Address Destination IP Address
The IP address of the destination for which a route is The IP address of the destination for which a route
desired is desired.
Destination Sequence Number Destination Sequence Number
The last sequence number received in the past by the The last sequence number received in the past by the
source for any route towards the destination. source for any route towards the destination.
Source IP Address Source IP Address
The IP address of the node which originated the Route The IP address of the node which originated the Route
Request Request.
Source Sequence Number Source Sequence Number
The current sequence number for route information The current sequence number for route information
generated by the source of the route request. generated by the source of the route request.
Extension:
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 | Multicast Grouphead IP Addr...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
...Multicast Grouphead IP Addr | Multicast Group Hop Count |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type xx
Length
The length of the extension field.
Multicast Grouphead IP Address
The IP Address of the Multicast Grouphead. This
extension is only used when a route to the Multicast
Grouphead is known.
Multicast Group Hop Count
The distance in hops of the node sending the RREQ from
the Multicast Grouphead. This extension is only used for
route rebuilding.
This extension is included only when a route to the multicast
grouphead is known.
5. Route Reply Message Format 5. Route Reply 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 |L| Reserved | Hop Count | | Type |L| Reserved | Hop Count |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Destination IP address | | Destination IP address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Destination Sequence Number | | Destination Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 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 xx Type xx
Reserved Sent as 0; ignored on reception. Reserved
Sent as 0; ignored on reception.
Hop Count The number of hops from the Source IP Address to the Hop Count
Destination IP Address. The number of hops from the Source IP Address to the
Destination IP Address. For multicast route requests
this indicates the number of hops to the multicast
grouphead.
L If the 'L' bit is set, the message is a "hello" message L If the 'L' bit is set, the message is a "hello"
and contains a list of the node's neighbors. message and contains a list of the node's neighbors.
Destination IP Address Destination IP Address
The IP address of the destination for which a route is The IP address of the destination for which a route is
supplied supplied.
Destination Sequence Number Destination Sequence Number
The destination sequence number associated to the route The destination sequence number associated to the
route.
Lifetime Lifetime The time for which nodes receiving the RREP consider
The time for which nodes receiving the RREP consider the the route to be valid.
route to be valid.
6. Node Operation Extension:
This section describes the scenarios under which nodes generate RREQs 0 1 2 3
and RREPs, and how the fields in the message are handled. 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 | Multicast Group IP Address ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
... Multicast Group IP Address | Multicast Grouphead IP Addr ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
... Multicast Grouphead IP Addr | Multicast Group Seq Number ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
... Multicast Group Seq Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
6.1. Maintaining Route Utilization Records Type xx
Length
The length of the extension field.
Multicast Group IP Address
The IP Address of the Multicast Group.
Multicast Grouphead IP Address
The IP Address of the Multicast Grouphead.
Multicast Group Sequence Number
The current sequence number of the Multicast Group.
This extension is included when responding to a multicast group route
request.
6. Multicast Route Invalidation Message Format
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Reserved | Hop Count |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Destination IP address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Destination Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Source IP address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Source Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The format of the Multicast Route Invalidation message is illustrated
above, and contains the following fields:
Type xx
Reserved
Sent as 0; ignored on reception.
Hop Count
The number of hops from the Source IP Address to the
Destination IP Address.
Destination IP Address
The IP address of the Multicast Group for which a route
is supplied.
Destination Sequence Number
The destination sequence number associated to the
Multicast Group.
Source IP Address
The IP address of the node which originated the Route
Request.
Source Sequence Number
The current sequence number for route information
generated by the source of the route request.
Extensions:
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 | Next Hop IP Address...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
...Next Hop IP Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type xx
Length
The length of the extension field
Next Hop IP Address
The IP address of the node chosen to be the next hop for
the multicast tree.
This extension is included when a source node wishes to invalidate
all but one of the routes set up by RREPs. It is not included when a
multicast tree member is pruning itself from the tree.
7. Node Operation - Unicast
This section describes the scenarios under which nodes generate
RREQs and RREPs for unicast communication, and how the fields in the
message are handled.
7.1. Maintaining Route Utilization Records
For each valid route maintained by a node (containing a finite For each valid route maintained by a node (containing a finite
metric), the node also maintains a list of those neighbors that are metric), the node also maintains a list of those neighbors that are
actively using the route. This active-list of neighbors will receive actively using the route. This active-list of neighbors will receive
notifications from the node in the event of detection of a link notifications from the node in the event of detection of a link
breakage. breakage.
6.2. Generating Route Requests 7.2. Generating Route Requests
A node broadcasts a RREQ when it determines that it needs a route to A node broadcasts a RREQ when it determines that it needs a route to
a destination and does not have one available. This can happen if a destination and does not have one available. This can happen if
the destination is previously unknown to the node, or if a previously the destination is previously unknown to the node, or if a previously
valid route to the destination expires. Routes can become invalid valid route to the destination expires. Routes can become invalid
if they time out (the Lifetime associated with the route expires), if they time out (the Lifetime associated with the route expires),
or else if a link breakage results in an infinite metric being or else if a link breakage results in an infinite metric being
associated with the route. When a route table entry is marked associated with the route. When a route table entry is marked
with an infinite metric, its expiration time is also updated to be with an infinite metric, its expiration time is also updated to be
the current time plus BAD_LINK_LIFETIME milliseconds. After the the current time plus BAD_LINK_LIFETIME milliseconds. After the
expiration time, the route MAY be expunged from the node's route expiration time, the route MAY be expunged from the node's route
table. table.
After broadcasting a RREQ a node waits for a RREP, and if the After broadcasting a RREQ a node waits for a RREP, and if the
reply is not received within RREP_WAIT_TIME seconds, the node may reply is not received within RREP_WAIT_TIME seconds, the node may
rebroadcast the RREQ. The RREQ may be rebroadcast up to a maximum of rebroadcast the RREQ. The RREQ may be rebroadcast up to a maximum of
RREQ_RETRIES times. Each rebroadcast has to increment the Broadcast RREQ_RETRIES times. Each rebroadcast has to increment the Broadcast
ID field. The node MAY choose to use larger TTL values in the IP ID field. The node MAY choose to use larger TTL values in the IP
header field, or wait for longer times for the RREP to arrive. header field, or wait for longer times for the RREP to arrive.
6.3. Forwarding Route Requests 7.3. Forwarding Route Requests
When a node receives a broadcast RREQ, it first checks to see When a node receives a broadcast RREQ, it first checks to see whether
whether it has received a RREQ with the same Source IP Address field it has received a RREQ with the same Source IP Address and broadcast
within the last BCAST_ID_SAVE milliseconds. If such a RREQ has ID fields within the last BCAST_ID_SAVE milliseconds. If such a RREQ
been received, the node silently discards the newly received RREQ. has been received, the node silently discards the newly received
Otherwise, the node checks to see whether it has a route to the RREQ. Otherwise, the node checks to see whether it has a route to
destination. If the node does not have a route, it rebroadcasts the the destination. If the node does not have a route, it rebroadcasts
RREQ from its interface(s) with the same field values, but using its the RREQ from its interface(s) with the same field values, but using
own IP address in the IP header of the outgoing RREQ. The TTL or hop its own IP address in the IP header of the outgoing RREQ. The TTL or
limit field in the outgoing IP header is decreased by one. The Hop hop limit field in the outgoing IP header is decreased by one. The
Count field in the broadcast RREQ message is incremented by one, Hop Count field in the broadcast RREQ message is incremented by one,
to account to the new hop through the intermediate node. In this to account to the new hop through the intermediate node. In this
case, the node also creates a reverse route to the Source IP Address case, the node also creates a reverse route to the Source IP Address
in its routing table with next hop equal to the IP address of the in its routing table with next hop equal to the IP address of the
neighboring node that sent the broadcast RREQ (often not equal to the neighboring node that sent the broadcast RREQ (often not equal to the
Source IP Address field in the RREQ message). This reverse route Source IP Address field in the RREQ message). This reverse route
might be used for an eventual RREP back to the original node making might be used for an eventual RREP back to the original node making
the RREQ (identified by the Source IP Address). The reverse route is the RREQ (identified by the Source IP Address). The reverse route is
put into the route table with lifetime REV_ROUTE_LIFE milliseconds. put into the route table with lifetime REV_ROUTE_LIFE milliseconds.
If, on the other hand, the node does have a route for the If, on the other hand, the node does have a route for the
destination, it compares the destination sequence number (dest-seqno) destination, it compares the destination sequence number (dest-seqno)
for that route with the Destination Sequence Number field of the for that route with the Destination Sequence Number field of the
incoming RREQ. If the node's existing dest-seqno is smaller than incoming RREQ. If the node's existing dest-seqno is smaller than
the Destination Sequence Number field of the RREQ, the node again the Destination Sequence Number field of the RREQ, the node again
rebroadcasts the RREQ just as if it did not have a route to the rebroadcasts the RREQ just as if it did not have a route to the
destination at all. destination at all.
In this case, the intermediate node MAY also transmit a RREQ
to the active-list associated with the stale route to that
destination?
If the node has a route to the destination, and the node's existing If the node has a route to the destination, and the node's existing
dest-seqno is greater than or equal to the Destination Sequence dest-seqno is greater than or equal to the Destination Sequence
Number of the RREQ, then the node generates a RREP as discussed Number of the RREQ, then the node generates a RREP as discussed
further in section 6.4. further in section 7.4.
6.4. Generating Route Replies 7.4. Generating Route Replies
If a node receives a route request for a destination, and has a If a node receives a route request for a destination, and has a
fresh enough route to satisfy the request, the node generates a RREP fresh enough route to satisfy the request, the node generates a RREP
message and unicasts it back to the node indicated by the Source message and unicasts it back to the node indicated by the Source
IP Address field of the received RREQ. First, the node copies over IP Address field of the received RREQ. First, the node copies over
its destination sequence number from the entry in its route table, its destination sequence number from the entry in its route table,
or if the generating node is the node itself, it uses a destination or if the generating node is the node itself, it uses a destination
sequence number at least equal to a sequence number generated after sequence number at least equal to a sequence number generated after
the last detected change in its neighbor set. If the node has not the last detected change in its neighbor set. If the node has not
detected any change in its set of neighbors since it last incremented detected any change in its set of neighbors since it last incremented
it destination sequence number, it may use the same destination its destination sequence number, it may use the same destination
sequence number. sequence number.
As part of the process of generating the RREP, the generating node As part of the process of generating the RREP, the generating node
creates or updates an entry in its routing table for the Source creates or updates an entry in its routing table for the Source
IP Address, if necessary as described in section 6.3. The Source IP Address, if necessary as described in section 7.3. The Source
Sequence Number is put into the route entry, along with the Hop Count Sequence Number is put into the route entry, along with the Hop Count
from the RREQ. The expiration time for the route table entry is set from the RREQ. The expiration time for the route table entry is set
to the current time plus ACTIVE_ROUTE_TIMEOUT seconds. to the current time plus ACTIVE_ROUTE_TIMEOUT seconds.
If the generating node is not the destination node, then the If the generating node is not the destination node, then the
generating node calculates the Hop Count between the Source IP generating node calculates the Hop Count between the Source IP
Address and the Destination IP Address by adding together the Hop Address and the Destination IP Address by adding together the Hop
Count from the RREQ and the hop count stored in the route table entry Count from the RREQ and the hop count stored in the route table entry
for the destination node. If, on the other hand, the generating node for the destination node. If, on the other hand, the generating node
is the destination node itself, the Hop Count field in the RREP is is the destination node itself, the Hop Count field in the RREP is
simply equal to the Hop Count received in the RREQ. simply equal to the Hop Count received in the RREQ.
If the node is not the destination node, it calculates the Lifetime If the node is not the destination node, it calculates the Lifetime
field of the RREQ by subtracting the current time from the expiration field of the RREP by subtracting the current time from the expiration
time in its route table entry. Otherwise, if the generating node is time in its route table entry. Otherwise, if the generating node is
also the destination node, it copies the value MY_ROUTE_TIMEOUT into also the destination node, it copies the value MY_ROUTE_TIMEOUT into
the Lifetime field of the RREP. the Lifetime field of the RREP.
If the generating node is not the node indicated by the Destination If the generating node is not the node indicated by the Destination
IP Address, then it puts the next hop towards the destination in the IP Address, then it puts the next hop towards the destination in the
active-list for the reverse path route entry. active-list for the reverse path route entry.
6.5. Generating Hello Messages 7.5. Generating Hello Messages
Every node generates a "hello" message once every HELLO_INTERVAL Every node generates a "hello" message once every HELLO_INTERVAL
milliseconds. This hello message is a broadcast IP RREP with TTL = milliseconds. This hello message is a broadcast RREP with TTL = 1,
1, and the message fields set as follows: and the 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 latest sequence number the latest sequence number
Hop Count 0 Hop Count 0
Lifetime (1 + ALLOWED_HELLO_LOSS) * HELLO_INTERVAL Lifetime (1 + ALLOWED_HELLO_LOSS) * HELLO_INTERVAL
6.6. Initiating Triggered Route Replies The Hello Messages MAY also contain extensions denoting the
multicast groups which are known to the node, along with the groups'
corresponding groupheads. These extensions can be used by nodes
which have just joined the network to fill in their Request Table
up-to-date request information. The information is also used for
route rebuilding, as is described later.
The extensions have the following format:
Multicast Group IP Address
IP address of known multicast group
Multicast Grouphead IP Address
IP Address of corresponding multicast grouphead
7.6. Initiating Triggered Route Replies
A node can trigger an unsolicited RREP if either it detects a link A node can trigger an unsolicited RREP if either it detects a link
breakage for a next hop along an active route in its route table, or breakage for a next hop along an active route in its route table, or
if it receives a RREP from a neighbor with an infinite metric for an if it receives a RREP from a neighbor with an infinite metric for an
active route (i.e., containing a Destination IP Address for which active route (i.e., containing a Destination IP Address for which
there is a route table entry with a nonempty active-list) there is a route table entry with a nonempty active-list)
The unsolicited RREP is unicast to each neighbor in the nonempty The unsolicited RREP is unicast to each neighbor in the nonempty
active-list for the route to that destination. The contents of the active-list for the route to that destination. The contents of the
RREP fields are set as follows: RREP fields are set as follows:
skipping to change at page 9, line 5 skipping to change at page 15, line 5
Hop Count 65,535 Hop Count 65,535
Destination IP Address Destination IP Address
The destination in the broken route The destination in the broken route
Destination Sequence Number Destination Sequence Number
One plus the destination sequence number recorded in One plus the destination sequence number recorded in
the route. the route.
6.7. Detecting Link Breakage 7.7. Detecting Link Breakage
A node can detect a link breakage by listening for "hello" messages A node can detect a link breakage by listening for "hello" messages
from its set of neighbors. If it has received hello messages from from its set of neighbors. If it has received hello messages from
a particular neighbor, but misses more than ALLOWED_HELLO_LOSS a particular neighbor, but misses more than ALLOWED_HELLO_LOSS
consecutive hello messages from that neighbor, the node can presume consecutive hello messages from that neighbor, the node can presume
that the particular neighbor is no longer able to maintain a direct that the particular neighbor is no longer able to maintain a direct
link with the mobile node. When this happens, the node should assume link with the mobile node. When this happens, the node should assume
that its link with the former neighbor has been broken, and proceed that its link with the former neighbor has been broken, and proceed
as in Section 6.6. A node should assume that a hello message has as in Section 7.6. A node should assume that a hello message has
been missed if it is not received within 1.5 times the duration of been missed if it is not received within 1.5 times the duration of
the HELLO_INTERVAL. the HELLO_INTERVAL.
Alternatively, the node can use any physical-layer or link-layer Alternatively, the node can use any physical-layer or link-layer
methods to detect link breakages with nodes it has considered as methods to detect link breakages with nodes it has considered as
neighbors. neighbors.
7. Configuration Parameters 8. Node Operation - Multicast
This section describes the scenarios under which nodes generate
RREQs, RREPs, and MINVs for multicast communication, and how the
fields in the messages are handled.
8.1. Maintaining Multicast Tree Utilization Records
For each valid multicast group (containing a finite metric) of
which a node is a part, either because it is a member of the group
or because it is a router for the multicast tree, the node also
maintains a list of those neighbors that are likewise a part of the
multicast tree. This active-list of neighbors is used for forwarding
messages received for the multicast group. A node will forward such
a message to every neighbor listed as a part of the multicast tree,
except that neighbor from which the message arrived.
8.2. Generating Multicast Route Requests
A node sends a route request (RREQ) either when it determines that it
should be a part of a multicast group, and it is not already a member
of that group, or when it has a message to send to the multicast
group but does not have a route to that group. If the node wishes to
join the multicast group, it sets the flag J in the RREQ; otherwise,
it leaves the flag unset. The destination address of the RREQ is
always set to the multicast group address. If the node has a record
of another node (the multicast grouphead) requesting to be a member
of that multicast group, it has two options. If the node has a known
route to the grouphead, it will place the address of that node in
the extension field and will unicast the RREQ to the corresponding
next hop for that destination. Otherwise, if the node does not have
a route to the grouphead, or if it does not know who the multicast
grouphead is, it will broadcast the RREQ with destination IP address
set to the IP address of the multicast group, and it will not include
the extension field.
These scenarios can occur during initialization of a node, when a
node discovers it should be a member of a multicast group, or when
a previously valid branch of the multicast tree expires. Branches
of the multicast tree become invalid if they time out (the Lifetime
associated with the route expires), or if a link breakage results in
an infinite metric being associated with the route.
The process of waiting for a RREP to a RREQ with a multicast
destination address is the same as that described in Section 7.2.
The node may resend the RREQ up to RREQ_RETRIES times if a RREP is
not received. If the original RREQ was unicast to a specific node
and a RREP is not received within RREP_WAIT_TIME seconds, the node
will broadcast the next RREQ (and all subsequent RREQs for that
multicast group) across the network. The destination IP address of
the rebroadcast is set to the address of the multicast group, and
the extension field containing the multicast grouphead address is
not included. If a RREP is not received after RREQ_RETRIES total
requests, the node may assume that there are no other members of
that particular group within the network. If it wanted to join the
multicast group, it will then become the multicast grouphead for that
multicast group and initialize the destination sequence number of
the multicast group. Otherwise, if it only wanted to send packets
to that group without actually joining the group, it will drop the
packets it had for that group.
Each node in the network receiving a RREQ message with the J flag
set, i.e. every member of the network, checks their Request Table
to see whether there is already an entry for this multicast group.
If there is no entry for the group, the node records the IP Address
of the node which sent the RREQ, together with the IP address of
the group for which it requested to be a member, in the Request
Table. Because the first node to request to be in a group becomes
the multicast grouphead, entries in the Request Table represent
multicast groupheads. If a node wishes to join or send a message to
a multicast group in the future, it will first consult its Request
Table to see if another node had previously requested to join that
group. Based on the existence or nonexistence of an entry for the
multicast group in the Request Table, the node will then send the
RREQ as described at the beginning of the section.
8.3. Forwarding Multicast Route Requests
The operation of nodes forwarding RREQs for multicast is similar
to that for the reception and forwarding of RREQs as described in
Section 7.3, with the following exceptions. If the RREQ is a join
request, when the node creates a reverse route to the Source IP
Address, it places a route pointer in its multicast routing table, in
addition to its (unicast) routing table. Further, a node can only
respond to a join RREQ if it is a member of the multicast tree. The
generation of the route reply (RREP) message is discussed in the
following section.
8.4. Generating Multicast Route Replies
If a node receives a multicast join route request for a multicast
group, and it is already a member of the multicast tree for that
group, the node updates its route and multicast route tables and
then generates a RREP message. It unicasts the RREP back to the
node indicated by the Source IP Address field of the received
RREQ. The RREP contains the current destination sequence number for
the multicast group, as well as the IP address of the multicast
grouphead.
If a node receives a multicast join route request for a multicast
group and it is not already a member of the multicast tree for that
group, it will rebroadcast the RREQ to its neighbors.
If a node receives a multicast route request that is not a join
message, it can reply if it has a route to the multicast tree.
Otherwise it will continue forwarding the message.
In the event that a node receives a unicasted multicast route request
that specifies its own IP address as the destination address (i.e.
the source node believes this destination node to be the multicast
grouphead), but the node is in fact not the grouphead, it can simply
ignore the RREQ. The source node will time out after RREP_WAIT_TIME
seconds and will broadcast a new RREQ without the grouphead address
specified.
Every time the Multicast Grouphead sends an RREP in response to a
RREQ, it increments the multicast group sequence number by one and
attaches the new value of the sequence number to the RREP.
Regardless of whether the multicast grouphead or an intermediate node
generates the RREP, the RREP fields are set as follows:
Hop Count The distance in hops the node initiating the RREP
is from the multicast grouphead. This field is
incremented by each node that forwards the RREP along
the route to the source.
Destination IP Address
The IP address of the destination for which a route
is supplied, in this case the multicast grouphead.
Destination Sequence Number
The destination sequence number associated with the
route to the grouphead.
Lifetime The time for which nodes receiving the RREP consider
the route to be valid.
Multicast Group IP Address
The IP Address of the Multicast Group.
Multicast Grouphead IP Address
The IP Address of the Multicast Grouphead.
Multicast Group Sequence Number
The current sequence number of the Multicast Group.
8.5. Route Deletion and Multicast Tree Pruning
When a node broadcasts an RREQ message, it is likely to receive more
than one reply since any node in the multicast tree can respond.
If the RREQ was a join request, the RREP message traveling back
to the node which originated the request sets up route pointers,
effectively grafting a branch onto the multicast tree. If multiple
branches to the same destination are created in such a manner, a
loop will be formed. Hence, in order to prevent the formation of
any such loops, it is necessary to delete all but one of the routes
created by the RREP messages. The RREP containing the largest
destination sequence number is chosen to be the added branch to the
multicast tree. In the event that a node receives more than one
RREP with the same (largest) sequence number, it selects the first
one with the smallest hop count, i.e. the shortest distance to the
multicast grouphead. After waiting for RREP_WAIT_TIME seconds,
the node must then deactivate all routes created by other RREPs.
This is accomplished by broadcasting a multicast-invalidate (MINV)
message. The Destination IP Address of the MINV packet is set to the
IP address of the multicast group, and the IP address of the next hop
along the branch which was added to the multicast tree is included
in an extension field. The Hop Count field of the MINV is set to 1.
All nodes receiving this message whose address does not match that
listed in the extension field of the packet will delete the multicast
tree pointer to the node from which the packet came. The node which
was chosen as the next hop sets the 'active' flag for the sending
node to true, thereby finalizing the creation of the tree branch.
Various scenarios exist for the nodes receiving the MINV message.
If the node receiving this message is a member of the multicast
group, it will not forward the MINV any further. If it is not a
member of the multicast group and no other nodes use it as a router
for the multicast group, it will propagate the MINV further up the
tree, effectively removing (pruning) itself from the multicast tree.
The Destination IP Address of the propagated MINV message is set
to the IP address of the multicast group, and the extension field
indicating the next hop is not included. The lack of the next hop
extension field indicates to all nodes receiving the packet that
their multicast tree route pointer to this source node (if such a
route pointer exists) should be deleted. If the next hop selected
by the source node's MINV message was not previously a multicast
tree member, it will have propagated the original RREQ further up
the network in search of nodes which are tree members. Thus it is
possible that this node also received more than one RREP. When the
node receives more than one RREP for the same RREQ, it operates in
a manner similar to the source node by saving the route information
with the greatest sequence number, and beyond that the lowest hop
count; it discards all other RREPs. This node forwards the first
RREP towards the source of the RREQ, and then forwards later RREPs
only if they have a greater sequence number or smaller metric. When
the node receives an MINV announcing it as the next hop, it will
send its own MINV announcing the node it has chosen as its next hop,
and so on up the tree, until a node which was already a part of the
multicast tree is reached. If a node receives an MINV and discovers
it was not chosen as the next hop and is not otherwise a part of the
multicast tree, it will delete the tree pointers and send an MINV
without the next hop extension field to prune itself from the tree.
When a source node sends an MINV selecting a next hop, it sets the
'active' flag for this next hop to true. If the next hop also needs
to send an MINV message specifying which node it has chosen as its
next hop, it lists the IP address of this next hop in the next hop
extension of the MINV. Upon receiving this MINV message, the source
node will not delete the tree pointer to this node (even though its
IP address is not listed in the next hop extension) because the
'active' flag has already been set.
To prevent the possibility of multicast group data messages being
delivered to the source node from multiple neighboring nodes before
the MINV messages is broadcast, no node is allowed to forward a data
packet to this source node before the reception of the MINV message.
The nodes know they have not yet received the MINV message because
the 'active' flag for that tree branch remains unset. Only after
receiving the MINV and setting the 'active' flag can the node to
which the MINV is addressed forward any multicast group data packets
to the node.
If a multicast group member revokes its member status and wishes to
remove itself from the multicast tree, it can do so if it is not a
multicast router for any other nodes in the multicast group. If this
is the case, it may broadcast an MINV message without the next hop
extension and with the Destination IP Address set to the IP address
of the multicast group to prune itself from the tree. Similarly,
if the node receiving this message is not a member of the multicast
group and does not have any other nodes routing through it, it may
send its own MINV message up the tree.
8.6. Repairing Link Breakages
When a link breakage is detected between two nodes on the multicast
tree, the node upstream of the break (i.e. the node which is further
from the multicast grouphead) is responsible for initiating the
repair of the broken link. In order to build the route back up, this
node will broadcast a RREQ with destination IP address set to the IP
address of the grouphead and with the J flag set. The destination
sequence number of the RREQ is the last known sequence number of the
multicast group. The Multicast Group Hop Count field is set to the
distance of the source node from the multicast grouphead. Only a
node which has a hop count for the multicast group smaller than the
indicated value can respond. This hop count requirement is included
to prevent nodes on the same side of the break as the node initiating
the repair from replying to the RREQ. The RREQ is broadcast using an
expanding rings search. Because of the high probability that other
nearby nodes can be used to rebuild the route to the grouphead, the
original RREQ is broadcast with a TTL (time to live) field value
equal to the Multicast Group Hop Count. In this way, the effects of
the link breakage may be localized. If no reply is received within
RREP_WAIT_TIME seconds, the RREQ will be rebroadcast with a larger
TTL value, and so on until the message is broadcast across the entire
network or until the route is rebuilt. Any node that is a part of
the multicast tree and which had a multicast group hop count smaller
than that contained in the RREQ can return an RREP. If there is more
than one RREP received at the originating node, route deletions occur
as described in the previous section.
If no response is received after RREQ_RETRIES broadcasts, it can be
assumed that the network has become partitioned and the multicast
tree cannot be repaired at this time. In this situation, the
node which had initiated the route rebuilding becomes the new
multicast grouphead for its part of the multicast tree partition.
It broadcasts a RREP with an infinity metric and with the multicast
group address extension field containing the corresponding multicast
group IP address included. All nodes receiving this RREP update
their Request Tables to indicate the new grouphead information.
Nodes which are a part of the multicast group also update the
grouphead information for that group in their Multicast Route Table
to indicate the new grouphead. All nodes will change the information
in their hello messages to reflect this update.
In the event that the link break could not be repaired, the multicast
tree will remain partitioned until the two parts of the network
become connected once again. A node from one partition of the
network will know that it has come into contact with a node from
the other side of the network by noting the difference in the hello
message multicast group information. The node who is a part of the
network partition with the lower grouphead IP address will initiate
the tree repair. It will unicast a RREQ message with the R flag set
back to the multicast grouphead of its partition in order to get
permission to rebuild the tree. The node must seek permission to
rebuild the tree in order to prevent multiple nodes from attempting
to rebuild the tree if contact between the two partitions is
re-established in more than one place. Multiple repairs would create
loops within the multicast tree. Additionally, since the node
initiating the repair is not necessarily a multicast tree member, it
may itself have become disconnected from the multicast grouphead on
its side of the partition, and so the lack of reply will prevent it
from attempting to repair the tree. The grouphead is the only node
which can respond to an RREQ with the R flag set. It will respond to
the request by sending an RREP granting permission to one and only
one node to rebuild the tree. Any nodes which requested permission
and which do not receive an RREP will time out and not attempt the
repair. As the RREP travels back to the node, it will establish a
multicast tree branch if one did not already exist. After receiving
the RREP, the node which sent the repair request will unicast a RREQ
to the grouphead of the other network partition, using the node it
had received the hello message from as the next hop. This RREQ will
contain the current value of the partitions multicast group sequence
number. Upon receiving the RREQ, the multicast grouphead will take
the larger of its and the received multicast group sequence number,
increment this value by one, and respond with a RREP. As the RREP
is propagated back to the source node, a branch on to the multicast
tree is added. When the initiating node receives the RREP, it will
broadcast across the network an RREP with an infinity metric and the
multicast group address extension field containing the corresponding
multicast group IP address, and with the multicast grouphead IP
address and multicast group sequence number fields set to show the
updated information. All nodes receiving this RREP (i.e. the entire
connected portion of the network), will have the updated multicast
group information for that group. The node which was the grouphead
of the other partition will also note this message and update its
tables to indicate that the other grouphead is now the multicast
grouphead for the entire network.
8.7. Initiating Triggered Route Replies
A node can trigger an unsolicited RREP if it has an entry in its
Request Table for a multicast group, sends a RREQ to join the
multicast group, and after RREQ_RETRIES times does not receives a
response. The node will then become the new multicast grouphead, and
it will broadcast a RREP with infinity metric and with the multicast
group / grouphead extension information set to reflect that it is
now the grouphead for the multicast group. In addition, in order to
ensure nodes maintain consistent and up-to-date information about
who the multicast groupheads are, any node which is a grouphead for
a multicast group will broadcast an unsolicited RREP containing its
IP Address and the multicast group IP address for which it is the
grouphead across the network every RREP_UPDATE seconds. The contents
of the RREP fields are set as follows:
L 0
Hop Count 65,535
Destination IP Address
The IP Address of the node sending the RREP.
Destination Sequence Number
One plus the destination sequence number recorded in
the route.
Multicast Group IP Address
The IP Address of the Multicast Group of which the
node just became the grouphead.
Multicast Grouphead IP Address
The IP Address of the new Multicast Grouphead, i.e.
the node sending the RREP.
Multicast Group Sequence Number
The Sequence Number of the multicast group, as set by
the new multicast grouphead.
9. Configuration Parameters
This section gives default values for some important values This section gives default values for some important values
associated with AODV protocol operations. associated with AODV protocol operations.
ACTIVE_ROUTE_TIMEOUT 300 ACTIVE_ROUTE_TIMEOUT 3000
ALLOWED_HELLO_LOSS 2 ALLOWED_HELLO_LOSS 2
BAD_LINK_LIFETIME 3000 BAD_LINK_LIFETIME 2 * RREP_WAIT_TIME
BCAST_ID_SAVE 3000 BCAST_ID_SAVE 3000
HELLO_INTERVAL 1000 HELLO_INTERVAL 1000
NETWORK_DIAMETER 100 NET_DIAMETER 35
NODE_TRAVERSAL_TIME 400 NODE_TRAVERSAL_TIME 40
MY_ROUTE_TIMEOUT 600 MY_ROUTE_TIMEOUT 6000
REV_ROUTE_LIFE 3000 REV_ROUTE_LIFE RREP_WAIT_TIME
RREP_WAIT_TIME 3 * NODE_TRAVERSAL_TIME * NETWORK_DIAMETER RREP_UPDATE 5000
RREP_WAIT_TIME 3 * NODE_TRAVERSAL_TIME * NET_DIAMETER / 2
RREQ_RETRIES 3 RREQ_RETRIES 3
8. Extensions Note that the network may contain more than NET_DIAMETER ** 2 nodes.
NET_DIAMETER measures the number of "cells" (typically wireless) that
would have to be placed end to end in order to cover the area of the
network.
RREQ and RREP messages may have extensions defined in future versions 10. Extensions
of the protocol. These extensions will have the following format:
RREQ, RREP, and MINV messages may have further extensions defined
in future versions of the protocol. These extensions will 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 xx Type xx
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.
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 with rules for extensions will be spelled out more fully, and conform with
the rules for handling IPv6 options. the rules for handling IPv6 options.
9. Security Considerations 11. Security Considerations
Currently, AODV does not specify any special security measures. Currently, AODV does not specify any special security measures.
Route protocols, however, are prime targets for impersonation Route protocols, however, are prime targets for impersonation
attacks, and must be protected by use of authentication techniques attacks, and must be protected by use of authentication techniques
involving generation of unforgeable and cryptographically strong involving generation of unforgeable and cryptographically strong
message digests or digital signatures. It is expected that, in message digests or digital signatures. It is expected that, in
environments where security is an issue, that IPSec authentication environments where security is an issue, that IPSec authentication
headers will be deployed along with the necessary key management to headers will be deployed along with the necessary key management to
distribute keys to the members of the ad hoc network using AODV. distribute keys to the members of the ad hoc network using AODV.
References References
[1] S. Bradner. Key words for use in RFCs to Indicate Requirement [1] S. Bradner. Key Words for Use in RFCs to Indicate Requirement
Levels. RFC 2119, March 1997. Levels. RFC 2119, March 1997.
[2] Charles E. Perkins. Terminology for Ad-Hoc Networking. [2] Charles E. Perkins. Terminology for Ad-Hoc Networking.
draft-ietf-manet-terms-00.txt, November 1997. (work in draft-ietf-manet-terms-00.txt, November 1997. (work in
progress). progress).
Author's Address Author's Address
Questions about this memo can be directed to: Questions about this memo can be directed to:
Charles E. Perkins Charles E. Perkins
Sun Microsystems Sun Microsystems
901 San Antonio Rd. 901 San Antonio Rd.
Palo Alto, CA, 94303 Palo Alto, CA 94303
USA USA
1 650 786 6464 1 650 786 6464
1 650 786 6445 (fax) 1 650 786 6445 (fax)
cperkins@eng.sun.com cperkins@eng.sun.com
Elizabeth M. Royer
Dept of Electrical and Computer Engineering
University of California, Santa Barbara
Santa Barbara, CA 93106
1 805 893 7788
1 805 893 3262 (fax)
eroyer@alpha.ece.ucsb.edu
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