Mobile Ad Hoc Networking Working Group Charles E. Perkins INTERNET DRAFT Sun Microsystems Laboratories 20 November 1998 Elizabeth M. Royer University of California, Santa Barbara Ad Hoc On Demand Distance Vector (AODV) Routing draft-ietf-manet-aodv-02.txt Status of This Memo This document is a submission by the Mobile Ad Hoc Networking Working Group of the Internet Engineering Task Force (IETF). Comments should be submitted to the manet@itd.nrl.navy.mil mailing list. Distribution of this memo is unlimited. This document is an Internet-Draft. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet- Drafts as reference material or to cite them other than as ``work in progress.'' To view the entire list of current Internet-Drafts, please check the ``1id-abstracts.txt'' listing contained in the Internet-Drafts Shadow Directories on ftp.is.co.za (Africa), ftp.nordu.net (Northern Europe), ftp.nis.garr.it (Southern Europe), munnari.oz.au (Pacific Rim), ftp.ietf.org (US East Coast), or ftp.isi.edu (US West Coast). Abstract The Ad Hoc On-Demand Distance Vector (AODV) routing protocol is intended for use by mobile nodes in an ad hoc network characterized by frequent changes in link connectivity to each other caused by relative movement. It offers quick adaptation to dynamic link conditions, low processing and memory overhead, low network utilization, and establishment of both unicast and multicast routes between sources and destinations which are loop free at all times. It makes use of destination sequence numbers, which are a novel means of ensuring loop freedom even in the face of anomalous delivery of routing control messages, and solving classical problems associated with distance vector protocols, including the problem of ``counting to infinity''. Perkins, Royer Expires 20 April 1999 [Page i] Internet Draft AODV 20 November 1998 Contents Status of This Memo i Abstract i 1. Introduction 1 2. Overview 1 3. AODV Terminology 3 4. Route Request (RREQ) Message Format 5 5. Route Reply (RREP) Message Format 6 6. Node Operation - Unicast 7 6.1. Maintaining Route Utilization Records . . . . . . . . . . 7 6.2. Generating Route Requests (RREQs) . . . . . . . . . . . . 8 6.3. Forwarding Route Requests . . . . . . . . . . . . . . . . 8 6.4. Generating Route Replies (RREPs) . . . . . . . . . . . . 9 6.5. Maintaining Local Connectivity . . . . . . . . . . . . . 10 6.6. Initiating Triggered Route Replies (Triggered RREPs) . . 11 7. Multicast Route Activation (MACT) Message Format 12 8. Node Operation - Multicast 13 8.1. Maintaining Multicast Tree Utilization Records . . . . . 13 8.2. Generating Multicast RREQs . . . . . . . . . . . . . . . 13 8.3. Forwarding Multicast Route Requests . . . . . . . . . . . 14 8.4. Generating Multicast Route Replies . . . . . . . . . . . 14 8.5. Forwarding Route Replies . . . . . . . . . . . . . . . . 15 8.6. Route Deletion and Multicast Tree Pruning . . . . . . . . 16 8.7. Repairing Link Breakages . . . . . . . . . . . . . . . . 17 8.8. Initiating Triggered Route Replies . . . . . . . . . . . 19 9. Quality of Service 20 10. AODV and Aggregated Networks 20 11. Using AODV with Other Networks 21 12. Extensions 21 12.1. Hello Interval Extension Format . . . . . . . . . . . . . 22 12.2. Multicast Group Leader Extension Format . . . . . . . . . 22 12.3. Multicast Group Information Extension Format . . . . . . 23 Perkins, Royer Expires 20 April 1999 [Page ii] Internet Draft AODV 20 November 1998 12.4. Maximum Delay Extension Format . . . . . . . . . . . . . 24 12.5. Minimum Bandwidth Extension Format . . . . . . . . . . . 24 13. Configuration Parameters 25 14. Security Considerations 26 1. Introduction The Ad Hoc On-Demand Distance Vector (AODV) algorithm enables dynamic, self-starting, multihop routing between participating mobile nodes wishing to establish and maintain an ad hoc network. AODV allows mobile nodes to obtain routes quickly for new destinations, and does not require nodes to maintain routes to destinations that are not in active communication. Additionally, AODV allows for the formation of multicast groups whose membership is free to change during the lifetime of the network. AODV allows mobile nodes to respond quickly to link breakages and changes in network topology. The operation of AODV is loop free, and by avoiding the Bellman-Ford ``counting to infinity'' problem offers quick convergence when the ad hoc network topology changes (typically, when a node moves in the network). One distinguishing feature of AODV is its use of a destination sequence number for each route entry. The destination sequence number is created by the destination or the multicast group leader for any usable route information it sends to requesting nodes. Using destination sequence numbers ensures loop freedom and is simple to program. Given the choice between two routes to a destination, a requesting node always selects the one with the greatest sequence number. Another feature of AODV is that link breakages cause immediate notifications to be sent to the affected set of nodes, but only that set of nodes. 2. Overview Route Requests (RREQs), Route Replies (RREPs), and Multicast Route Activations (MACTs) are the three message types defined by AODV. These message types are handled by UDP, and normal IP header processing applies. So, for instance, the requesting node is expected to use its IP address as the source IP address for the messages. The range of dissemination of broadcast RREQs can be indicated by the TTL in the IP header. Fragmentation is typically not required. Perkins, Royer Expires 20 April 1999 [Page 1] Internet Draft AODV 20 November 1998 As long as the endpoints of a communication connection have valid routes to each other, AODV does not play any role. When a route to a new destination (either a single node or a multicast group) is needed, the node uses a broadcast RREQ to find a route to the destination. A route can be determined when the RREQ reaches either the destination itself, or an intermediate node with a fresh enough route to the destination. The route is made available by unicasting a RREP back to the source of the RREQ. Since each node receiving the request caches a route back to the source of the request, the RREP can be unicast back from the destination to the source, or from any intermediate node that is able to satisfy the request back to the source. RREQs are also used when a node wishes to join a multicast group. A join flag in the RREQ informs nodes that when receiving the RREP, they are not just setting route pointers but are also setting multicast route pointers, which will be used if the route is selected to be added onto the tree. In case AODV cannot rely on lower-level mechanisms for neighborhood determination, a special ``hello'' message is defined for use at the network layer. For multicast groups, a ``Group Hello'' message is broadcast across the network by the multicast group leader. The message carries multicast group and corresponding group leader 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 management. Route table information must be kept even for ephemeral routes, such as are created to temporarily keep track of reverse paths towards nodes originating RREQs. AODV assumes the following fields exist in each route table entry: - Destination IP Address - Destination Sequence Number - Hop Count - Next Hop - Lifetime - Routing Flags The following information is stored in each entry of the multicast route table for multicast tree routes: - Multicast Group IP Address - Multicast Group Leader IP Address - Multicast Group Sequence Number - Hop Count to next Multicast Group member - Hop Count to Multicast Group leader Perkins, Royer Expires 20 April 1999 [Page 2] Internet Draft AODV 20 November 1998 - Next Hops - Lifetime The Next Hops field is a linked list of structures, each of which contains the IP address of a neighbor in the multicast tree. The IP Address of a Next Hop is only used to forward multicast messages after a MACT message has activated the route (see Section 8.6). 3. AODV Terminology This protocol specification uses conventional meanings [1] for capitalized words such as MUST, SHOULD, etc., to indicate requirement levels for various protocol features. This section defines other terminology used with AODV that is not already defined in [2]. forwarding node A node which agrees to forward packets destined for another destination node, by retransmitting them to a next hop which is closer to the destination along a path which has been set up using routing control messages. group leader 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 and maintaining 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 where 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). Perkins, Royer Expires 20 April 1999 [Page 3] Internet Draft AODV 20 November 1998 subnet leader A node which is a member of the subnet defined by a specific routing prefix, and which offers reachability to every other node with the same routing prefix. The subnet leader is responsible for initializing and maintaining the destination sequence number for every node on the subnet. Perkins, Royer Expires 20 April 1999 [Page 4] Internet Draft AODV 20 November 1998 4. Route Request (RREQ) 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 |J|R| Reserved | Hop Count | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Broadcast ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Destination IP address | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Destination Sequence Number | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Source IP address | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Source Sequence Number | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The format of the Route Request message is illustrated above, and contains the following fields: Type xx J Join flag; set when source node wants to join a 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. Hop Count The number of hops from the Source IP Address to the node handling the request. Broadcast ID A sequence number uniquely identifying the particular RREQ when taken in conjunction with the source node's IP address. Destination IP Address The IP address of the destination for which a route is desired. Destination Sequence Number The last sequence number received in the past by the source for any route towards the destination. Perkins, Royer Expires 20 April 1999 [Page 5] Internet Draft AODV 20 November 1998 Source IP Address The IP address of the node which originated the Route Request. Source Sequence Number The current sequence number to be used for route entries pointing to (and generated by) the source of the route request. When a node wishes to repair a multicast tree, it appends the Multicast Group Leader extension (see Section 12.2). 5. Route Reply (RREP) Message Format 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type |L|R|U| Reserved| Prefix Size | Hop Count | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Destination IP address | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Destination Sequence Number | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Lifetime | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The format of the Route Reply message is illustrated above, and contains the following fields: Type xx L If the `L' bit is set, the message is a ``hello'' message and contains a list of the node's neighbors. R Repair flag; set when a node wants to initiate a repair to connect two previously disconnected portions of the multicast tree. U Update flag; set in a Group Hello, when the group leader information has changed. Reserved Sent as 0; ignored on reception. Prefix Size If nonzero, the Prefix Size specifies that the indicated route vector may be used for any nodes with the same routing prefix (as defined by the Prefix Size) as the requested destination. Perkins, Royer Expires 20 April 1999 [Page 6] Internet Draft AODV 20 November 1998 Hop Count The number of hops from the Source IP Address to the Destination IP Address. For multicast route requests this indicates the number of hops to the multicast group leader. Destination IP Address The IP address of the destination for which a route is supplied. Destination Sequence Number The destination sequence number associated to the route. Lifetime The time for which nodes receiving the RREP consider the route to be valid. When the RREP is sent for a multicast destination, the Multicast Group Information extension is appended (see Section 12.3). 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 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 guarantee reachability to all the hosts sharing the indicated subnet prefix. The Subnet Leader is also responsible for maintaining the Destination Sequence Number for the whole subnet. 6. 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. 6.1. Maintaining Route Utilization Records For each valid route maintained by a node (containing a finite metric), the node also maintains a list of those neighbors that are actively using the route. This active-list of neighbors will receive notifications from the node in the event of detection of a link breakage. A neighbor is on the active list if it has sent any packet to the node to be forwarded to the destination within the last ACTIVE_ROUTE_TIMEOUT milliseconds. Perkins, Royer Expires 20 April 1999 [Page 7] Internet Draft AODV 20 November 1998 6.2. Generating Route Requests (RREQs) 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 the destination is previously unknown to the node, or if a previously valid route to the destination expires or is broken (i.e., an infinite metric is associated with the route). When a route table entry is marked with an infinite metric, its expiration time is also updated to be the current time plus BAD_LINK_LIFETIME milliseconds. After the expiration time, the route MAY be expunged from the node's route table. After broadcasting a RREQ a node waits for a RREP, and if the reply is not received within RREP_WAIT_TIME milliseconds, the node may rebroadcast the RREQ. The RREQ may be rebroadcast up to a maximum of RREQ_RETRIES times. Each rebroadcast has to increment the Broadcast 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. 6.3. Forwarding Route Requests When a node receives a broadcast RREQ, it first checks to see whether it has received a RREQ with the same Source IP Address and a broadcast ID field of equal unsigned integer value within the last BCAST_ID_SAVE milliseconds. If such a RREQ has been received, the node silently discards the newly received RREQ. Otherwise, the node checks to see whether it has a route to the destination. If the node does not have a route, it rebroadcasts the RREQ from its interface(s) but using its own IP address in the IP header of the outgoing RREQ. The TTL or hop limit field in the outgoing IP header is decreased by one. The Hop Count field in the broadcast RREQ message is incremented by one, to account for the new hop through the intermediate node. In this case, the node also creates or updates a reverse route to the Source IP Address 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 Source IP Address field in the RREQ message). This reverse route might be used for an eventual RREP back to the node which originated the RREQ (identified by the Source IP Address). If no route exists for the Source IP address, or if an existing route would expire too soon, the reverse route is put into the route table with lifetime REV_ROUTE_LIFE milliseconds. If, on the other hand, the node does have a route for the destination, it compares the destination sequence number (dest-seqno) for that route with the Destination Sequence Number field of the incoming RREQ. If the node's existing dest-seqno is smaller than the Destination Sequence Number field of the RREQ, the node again Perkins, Royer Expires 20 April 1999 [Page 8] Internet Draft AODV 20 November 1998 rebroadcasts the RREQ just as if it did not have a route to the destination at all. 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 Number of the RREQ, then the node generates a RREP as discussed further in section 6.4. 6.4. Generating Route Replies (RREPs) 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 message and unicasts it back to the node indicated by the Source IP Address field of the received RREQ. If the node is not the destination node, it copies over the destination sequence number from the route table entry. If the generating node is the destination itself, it uses a destination sequence number at least equal to a sequence number generated after the last detected change in its neighbor set and at least equal to the destination sequence number in the RREQ. If the destination node has not detected any change in its set of neighbors since it last incremented its destination sequence number, it may use the same destination sequence number. As part of the process of generating the RREP, the generating node creates or updates an entry in its routing table for the Source IP Address, if necessary as described in section 6.3. The Source 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 to the current time plus ACTIVE_ROUTE_TIMEOUT milliseconds. If the generating node is not the destination node, then the generating node places its distance in hops from the destination in the Hop Count field. If the generating node is the destination node, it places the value zero in the Hop Count field. The Hop Count field is incremented by one at each hop as the RREP is forwarded to the source. When the RREP reaches the source, the Hop Count will represent the distance, in hops, of the destination from the source. If the node is not the destination node, it calculates the Lifetime field of the RREP by subtracting the current time from the expiration time in its route table entry. Otherwise, if the generating node is also the destination node, it copies the value MY_ROUTE_TIMEOUT into the Lifetime field of the RREP. Each node MAY make a separate determination about its value MY_ROUTE_TIMEOUT. 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 active-list for the reverse path route entry. Perkins, Royer Expires 20 April 1999 [Page 9] Internet Draft AODV 20 November 1998 6.5. Maintaining Local Connectivity Each forwarding node SHOULD keep track of which of its neighbors are active next hops (i.e., which next hops have been used to forward packets towards some destination within the last ACTIVE_ROUTE_TIMEOUT milliseconds). Each forwarding node SHOULD attempt to determine which of its active next hop neighbors are actually within its broadcast range by using the following procedure. When a forwarding node receives a (unicast or multicast) packet from one of its active neighbors, and retransmits the packet to the next hop, the node SHOULD NOT transmit any additional data for NEXT_HOP_WAIT milliseconds. Instead, the node SHOULD listen to see if the next hop retransmitted the packet. If the retransmission is detected, the node can assume that the next hop is still within its broadcast range, and can then resume transmission. Otherwise, the node SHOULD attempt to detect a response from the next hop, using the following methods: - Any suitable link-layer indication, e.g. a link-layer acknowledgement, or a CTS to receive the packet, or a RTS the packet to its own downstream next hop. - Receiving a ICMP ACK message from the next hop. - A RREQ unicast to the next hop, asking for a route to the next hop. - An ICMP Echo Request message unicast to the next hop. The ICMP ACK message SHOULD be sent to a forwarding node by a next hop which is also the destination IP address shown in the IP header of the packet, when the destination has not sent any packets to the forwarding node within the last HELLO_INTERVAL milliseconds. If the next hop cannot be detected by any of these methods, the forwarding node MUST assume that the link is broken, and take corrective action by following the methods specified in Section 6.6. A node MAY detect a link breakage by listening for broadcasts and ``hello'' messages from its set of neighbors. If it has received hello messages from a neighbor, but misses more than ALLOWED_HELLO_LOSS consecutive broadcasts or hello messages from that neighbor, the node MUST assume that its neighbor is no longer in the neighborhood. When this happens, the node SHOULD proceed as in Section 6.6. A node SHOULD assume that a hello message has been missed if it is not received within 2.1 times the duration of the HELLO_INTERVAL. Perkins, Royer Expires 20 April 1999 [Page 10] Internet Draft AODV 20 November 1998 A node MAY offer connectivity information by broadcasting local ``hello'' messages as follows. Every HELLO_INTERVAL milliseconds, the node checks whether it has sent a broadcast (e.g., a RREQ) within the last HELLO_INTERVAL. If it has not, it MAY generate a ``hello'' message. This hello message is a broadcast RREP with TTL = 1, and the message fields set as follows: Destination IP Address The node's IP address. Destination Sequence Number The node's latest sequence number. Hop Count 0 Lifetime (1 + ALLOWED_HELLO_LOSS) * HELLO_INTERVAL In addition to regular Hello messages, each multicast group leader will also broadcast a Group Hello message system-wide every GROUP_HELLO_INTERVAL milliseconds. This system-wide Group Hello message has IP TTL value greater than the diameter of the network and is initialized to a hop count of zero. The hop count value is incremented by one by each node as the message is forwarded. This Group Hello message contains the IP Addresses of the Multicast Groups for which the node is the Group Leader, along with the corresponding multicast group sequence numbers. Nodes in the multicast tree can use these messages to update their current distance from the group leader. The information in the message is also used for merging partitioned multicast trees, as is described later. See Section 12.3 for extensions needed to complete a GROUP_HELLO message. 6.6. Initiating Triggered Route Replies (Triggered RREPs) 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 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 there is a route table entry with a nonempty active-list) The unsolicited RREP is broadcast to inform each neighbor in the nonempty active-list for the route to that destination. The contents of the RREP fields are set as follows: L 0 Hop Count 255 (= infinity) Perkins, Royer Expires 20 April 1999 [Page 11] Internet Draft AODV 20 November 1998 Destination IP Address The destination in the broken route Destination Sequence Number One plus the destination sequence number recorded for the route. 7. Multicast Route Activation (MACT) 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 |P|G| Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Multicast Group IP address | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Source IP address | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Source Sequence Number | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The format of the Multicast Route Activation message is illustrated above, and contains the following fields: Type xx P Prune flag; set when a node wishes to prune itself from the tree, unset when the node is activating a tree link. G Group Leader flag; set by a multicast tree member that fails to repair a multicast tree link breakage, and indicates to the group member receiving the message that it should become the new multicast group leader. Reserved Sent as 0; ignored on reception. Multicast Group IP Address The IP address of the Multicast Group for which a route is supplied. Source IP Address The IP address of the node which originated the Route Request. Perkins, Royer Expires 20 April 1999 [Page 12] Internet Draft AODV 20 November 1998 Source Sequence Number The current sequence number for route information generated by the source of the route request. To prune itself from the tree (i.e., inactivate its last link to the multicast tree), a multicast tree member sends an MACT with the 'P' flag = 1 to the next hop. A multicast tree member that has more than one next hop to the multicast tree SHOULD NOT try to prune itself from the multicast tree. 8. Node Operation - Multicast This section describes the scenarios under which nodes generate RREQs, RREPs, and MACTs for multicast communication, and how the fields in the messages are handled. 8.1. Maintaining Multicast Tree Utilization Records For each multicast tree to which a node belongs, 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 next hops -- i.e., those neighbors that are likewise a part of the multicast tree. This list of next hops is used for forwarding messages received for the multicast group. A node will forward a multicast message to every such next hop, except that neighbor from which the message arrived. If there are multiple next hops, the forwarding operation MAY be performed by broadcasting the multicast packet to the node's neighbors; only the neighbors that belong to the multicast tree will continue to forward the multicast packet. 8.2. Generating Multicast RREQs A node sends a multicast 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 `J' flag 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 knows the group leader and has a route to it, the node will place the group leader's address in the Multicast Group Leader extension (Section 12.2), and will unicast the RREQ to the corresponding next hop for that destination. Otherwise, if the node does not have a route to the group leader, or if it does not know who the multicast group leader is, it will broadcast the RREQ and will not include the extension field. Perkins, Royer Expires 20 April 1999 [Page 13] Internet Draft AODV 20 November 1998 The process of waiting for a RREP to a RREQ with a multicast destination address is the same as that described in Section 6.2. The node may resend the RREQ up to RREQ_RETRIES times if a RREP is not received. If a RREQ was unicast to a group leader and a RREP is not received within RREP_WAIT_TIME milliseconds, the node will broadcast subsequent RREQs for that multicast group across the network. 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 connected portion of the network. If it wanted to join the multicast group, it MAY then become the multicast group leader 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 MAY check its 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 membership in a group becomes the multicast group leader, entries in the Request Table represent multicast group leaders. If the multicast group leader changes at any time, the nodes will note this change by updating their Request Table so that the node IP address matches that of the new group leader. If the node wishes to join or send a message to a multicast group, it first consults its Request Table. Based on the existence of an entry for the multicast group in this table, the node will then send the RREQ as described at the beginning of this 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 6.3, with one exception. If the RREQ is a join request, when the node creates a reverse route to the Source IP Address, it places the information in its Multicast Route table. 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 RREQ for a multicast group, and it is already a member of the multicast tree for that group, the node updates its Multicast Route Table 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 Perkins, Royer Expires 20 April 1999 [Page 14] Internet Draft AODV 20 November 1998 the current sequence number for the multicast group, the distance of the responding node from the nearest multicast group member, and the IP address of the group leader. Further information about the multicast group leader is entered into the Multicast Group Information extension (see Section 12.3). A node can only respond to a join RREQ if it is a member of the multicast tree. 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. 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. 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 group leader), but the node is in fact not the group leader, it can simply ignore the RREQ. The source node will time out after RREP_WAIT_TIME milliseconds and will broadcast a new RREQ without the group leader address specified. Regardless of whether the multicast group leader or an intermediate node generates the RREP, the RREP fields are set as follows: Hop Count Distance of the responding node to the nearest multicast group member. Destination IP Address The IP address of the node which supplies a route to the multicast group. Destination Sequence Number The destination sequence number of the node which supplies a route to the multicast group. Lifetime The time for which nodes receiving the RREP consider the route to be valid. The Multicast Group Information extension described in Section 12.3 is also included. 8.5. Forwarding Route Replies If an intermediate node receives a RREP in response to a RREQ that it has transmitted (or retransmitted on behalf of some other node), it increments the Hop Count and forward the RREP along the path to the source of the RREQ. Perkins, Royer Expires 20 April 1999 [Page 15] Internet Draft AODV 20 November 1998 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. 8.6. Route Deletion and Multicast Tree Pruning When a node broadcasts a 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, which may eventually graft 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 activate only 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 a member of the multicast group. After waiting for RREP_WAIT_TIME milliseconds, the node must choose the route it wishes to use as its link to the multicast tree. This is accomplished by sending a Multicast Activation (MACT) message. The Destination IP Address of the MACT packet is set to the IP address of the multicast group. The node will unicast this message to the selected next hop, effectively activating the route. After receiving this message, the node's neighbor to which the MACT was sent activates the route entry for the link in the multicast route table, thereby finalizing the creation of the tree branch. All neighbors not receiving this message will time out and delete that node as a next hop for the multicast group in their route tables, having never activated the route entry for that next hop. Two scenarios exist for a neighboring node receiving the MACT message. If this node was previously a member of the multicast tree, it will not propagate the MACT message any further. However, if the next hop selected by the source node's MACT 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, as noted in section 8.5. When the node receives an MACT announcing it as the next hop, it will send its own MACT announcing the node it has chosen as its next hop, Perkins, Royer Expires 20 April 1999 [Page 16] Internet Draft AODV 20 November 1998 and so on up the tree, until a node which was already a part of the multicast tree is reached. 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 (i.e., if it is a leaf node). If this is the case, it may unicast to its next hop on the tree an MACT message with the 'P' flag set and with the Destination IP Address set to the IP address of the multicast group in order 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 MACT message up the tree. 8.7. Repairing Link Breakages 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. When a link breakage is detected between two nodes on the multicast tree, the node downstream of the break (i.e., the node which is further from the multicast group leader) 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 group leader 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 group leader. Only a node which has a hop count for the multicast group less than or equal to 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 group leader, 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 milliseconds, all subsequent RREQs (up to RREQ_RETRIES total attempts) will be broadcast across the entire network. Any node that is a part of the multicast tree and that has a multicast group hop count smaller than that contained in the RREQ can return a 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, if the Perkins, Royer Expires 20 April 1999 [Page 17] Internet Draft AODV 20 November 1998 node which had initiated the route rebuilding was a multicast group member, it will become the new multicast group leader for its part of the multicast tree partition. It broadcasts a Group Hello with the multicast group address extension field containing the corresponding multicast group IP address included. The `U' flag in the Group Hello is set, indicating that there has been a change in the group leader information. All nodes receiving this message update their Request Tables to indicate the new group leader information. Nodes which are a part of the multicast tree also update the group leader information for that group in their Multicast Route Table to indicate the new group leader. On the other hand, if the node which had initiated the repair is not a multicast group member, there are two possibilities. If it only has one next hop for the multicast tree, it will unicast a MACT message, with the 'P' flag set, to its next hop, thereby indicating that it is pruning itself from the tree. The node receiving this message will note that it is coming from its upstream link, i.e., from a node that is closer to the group leader than it is. If the node receiving this message is a multicast group member, it will become the new group leader and will broadcast a Group Hello message as indicated above. If it is not a multicast group member and it only has one other next hop link, it will similarly prune itself from the tree and this process will continue until a multicast group member is reached. On the other hand, if the node which initiated the rebuilding is not a group member and it has more than one next hop for the tree, it cannot prune itself, since doing so would partition the tree. It instead chooses one of its next hops and sends an MACT with the 'G' flag set. This flag indicates that the next group member to receive this message should become the new group leader. If the node's next hop is a group member, this node will become the group leader. Otherwise, the node will unicast its own MACT message with the 'G' flag set to one of its next hops, and so on until a group member is reached. In the event that the link break can 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 partition of the network by noting the difference in the Group Hello message multicast group leader information. A node which is a part of the network partition with the lower group leader IP address and which is also a member of the multicast tree can initiate the tree repair. It will unicast a RREQ message with the `R' flag set back to the multicast group leader 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. The group leader is the only node which can respond to a RREQ with the `R' flag set. It will respond Perkins, Royer Expires 20 April 1999 [Page 18] Internet Draft AODV 20 November 1998 to the request by sending a RREP granting permission to one and only one node to rebuild the tree. Any nodes which requested permission and which do not receive a 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 group leader of the other network partition, using the node it had received the Group 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 group leader will take the larger of its and the received multicast group sequence number, increment this value by one, and respond with a RREP. This is the group leader which will become the leader of the reconnected multicast tree. 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, the tree will be reconnected. The next time the group leader broadcasts a Group Hello, it will set the `U' flag to indicate that there is a change in the group leader information and group members should update the corresponding information. The node which was the group leader of the other partition will also note this message and update its tables to indicate that the other group leader is now the multicast group leader for the entire network. 8.8. Initiating Triggered Route Replies A node can trigger an unsolicited RREP if it sends a RREQ to join a multicast group and after RREQ_RETRIES times does not receives a response. The node will then become the new multicast group leader, and it will broadcast a RREP with infinity TTL (a Group Hello message) and with the multicast group IP Address / Sequence number extension information set to reflect that it is now the group leader for the multicast group. In addition, in order to ensure nodes maintain consistent and up-to-date information about who the multicast group leaders are, any node which is a group leader for a multicast group will broadcast such a Group Hello across the network every GROUP_HELLO_INTERVAL milliseconds. The contents of the RREP fields (including the Multicast Group Information Extension) are set as follows: L 0 Hop Count 0 Destination IP Address The IP Address of the node sending the Group Hello. Destination Sequence Number The node's latest destination sequence number. Perkins, Royer Expires 20 April 1999 [Page 19] Internet Draft AODV 20 November 1998 Multicast Group IP Address The IP Address of the Multicast Group for which the node is the group leader. Multicast Group Sequence Number One plus the last known sequence number of the multicast group. Nodes receiving the Group Hello incrememt the Hop Count field by one before forwarding the message. 9. Quality of Service AODV currently provides some minimal controls to enable mobile nodes in an ad hoc network to specify, as part of a RREQ, certain Quality of Service parameters that a route to a destination must satisfy. In particular, a RREQ MAY include a Maximum Delay extension (see Section 12.4) or a Minimum Bandwidth extension (see Section 12.5). If, after establishment of such a route, any node along the path detects that the requested Quality of Service parameters can no longer be maintained, that node MUST originate a ICMP QOS_LOST message back to the node which had originally requested the now unavailable parameters. 10. AODV and Aggregated Networks 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 network. However, in some cases a collection of mobile nodes MAY operate in a fixed relationship to each other and share a common subnet prefix, moving together within an area where an ad hoc network 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 reachability for all other nodes on the subnet, by responding with a RREP message to any RREQ message requesting a route to any node with the subnet routing prefix. Call the single node the ``subnet router''. In order for a subnet router to operate the AODV protocol for the whole subnet, it has to maintain a destination sequence number for the entire subnet. In any such RREP message sent by the subnet router, the Prefix Length field of the RREP message MUST be set to the length of the subnet prefix. Other nodes sharing the subnet prefix SHOULD NOT issue RREP messages. Perkins, Royer Expires 20 April 1999 [Page 20] Internet Draft AODV 20 November 1998 11. Using AODV with Other Networks In some configurations, an ad hoc network may be able to provide connectivity between external routing domains that do not use AODV. If the points of contact to the other networks can act as subnet routers (see section 10) for any relevant networks within the external routing domains, then the ad hoc network can maintain connectivity to the external routing domains. Indeed, the external routing networks 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 network (call it an Infrastructure Router) has to act as a ``subnet router'' for every subnet of interest within the external network for which the Infrastructure Router can provide reachability. This includes the need for maintaining a destination sequence number for that external subnet. If multiple Infrastructure Routers offer reachability to the same external subnet, those Infrastructure Routers have to cooperate (by means outside the scope of this specification) to provide consistent AODV semantics for ad hoc access to those subnets. 12. Extensions RREQ, RREP, and MACT messages have extensions defined in this version (and, possibly, future versions) of the protocol. Extensions have the following format: 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | type-specific data ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ where: Type xx Length The length of the type-specific data, not including the Type and Length fields of the extension. Extensions with types between 128 and 255 may NOT be skipped. The rules for extensions will be spelled out more fully, and conform with the rules for handling IPv6 options. Perkins, Royer Expires 20 April 1999 [Page 21] Internet Draft AODV 20 November 1998 12.1. Hello Interval 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 | Hello Interval ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... Hello Interval, continued | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type xx Length The length of the extension field. Hello Interval The number of milliseconds between successive transmissions of a ``hello'' message (RREP). 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 to wait for subsequent such RREP messages. 12.2. Multicast Group Leader Extension Format This extension is appended to a RREQ by a node wishing to repair a multicast tree. 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 Group Hop Count | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Multicast Group Leader IP Address | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type xx Length The length of the extension. Multicast Group Hop Count The distance in hops of the node sending the RREQ from the Multicast Group Leader. Multicast Group Leader IP Address The IP Address of the Multicast Group Leader. This extension is only used for rebuilding a multicast tree branch. In that case, a route to the Multicast Group Leader was known before Perkins, Royer Expires 20 April 1999 [Page 22] Internet Draft AODV 20 November 1998 the need for the repair was discovered, and the IP address of the group leader is placed in the extension field. 12.3. Multicast Group Information Extension Format The following extension is used to carry additional information for the RREP message (see Section 5) when sent to establish a route to a multicast destination. 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 Group IP Address ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... Multicast Group IP Address | Multicast Group Seq Number ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... Multicast Group Seq Number | Multicast Group Ldr IP Addr .. +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ .. Multicast Group Ldr IP Addr | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type xx Length The length of the extension field. Multicast Group IP Address The IP Address of the Multicast Group. Multicast Group Seq Number The current sequence number of the Multicast Group. Multicast Group Ldr IP Addr The IP Address of the current Multicast Group Leader. This extension is included when responding to a multicast group RREQ. It is also used by a multicast group leader when sending a Group Hello. The extension fields indicate which group the node is the group leader of and the current sequence number for that group. For a Group Hello the Multicast Group Ldr IP Address field is not included, since this information is already indicated by the Destination IP Address field of the message. Perkins, Royer Expires 20 April 1999 [Page 23] Internet Draft AODV 20 November 1998 12.4. Maximum Delay 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 | Max Delay | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type xx Length The length of the extension field. Max Delay The number of seconds allowed for a transmission from the source to the destination. The Maximum Delay Extension can be appended to a RREQ by a requesting node in order to place a maximum bound on the acceptable time delay experienced on any acceptable path from the source to the destination. Before forwarding the RREQ, an intermediate node MUST compare its NODE_TRAVERSAL_TIME to the (remaining) Max Delay indicated in the Maximum Delay Extension. If the Max Delay is less, the node MUST discard the RREQ and not process it any further. Otherwise, the node subtracts NODE_TRAVERSAL_TIME from the Max Delay value in the extension and continues processing the RREQ as specified in Section 6.3. 12.5. Minimum Bandwidth 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 | Minimum Bandwidth ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... Minimum Bandwidth | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type xx Length The length of the extension field. Minimum Bandwidth The amount of bandwidth (in kilobits/sec) needed for acceptable transmission from the source to the destination. Perkins, Royer Expires 20 April 1999 [Page 24] Internet Draft AODV 20 November 1998 The Minimum Bandwidth Extension can be appended to a RREQ by a requesting node in order to specify the minimal amount of bandwidth that must be made available along acceptable path from the source to the destination. Before forwarding the RREQ, an intermediate node MUST compare its available link capacity to the Minimum Bandwidth indicated in the extension. If the requested amount of bandwidth is not available, the node MUST discard the RREQ and not process it any further. Otherwise, the node continues processing the RREQ as specified in Section 6.3. 13. Configuration Parameters This section gives default values for some important values associated with AODV protocol operations. A particular mobile node may wish to change certain of the parameters, in particular the NET_DIAMETER, MY_ROUTE_TIMEOUT, MY_TRAVERSAL_TIME, ALLOWED_HELLO_LOSS, RREQ_RETRIES, and possibly the HELLO_INTERVAL. In the latter case, the node should advertise the HELLO_INTERVAL in its ``hello'' messages, by appending a Hello Interval Extension to the RREP message. ACTIVE_ROUTE_TIMEOUT 3000 ALLOWED_HELLO_LOSS 2 BAD_LINK_LIFETIME 2 * RREP_WAIT_TIME BCAST_ID_SAVE 30000 GROUP_HELLO_INTERVAL 5000 HELLO_INTERVAL 1000 MTREE_BUILD 2 * REV_ROUTE_LIFE NET_DIAMETER 35 NEXT_HOP_WAIT NODE_TRAVERSAL_TIME + 10 NODE_TRAVERSAL_TIME 40 MY_TRAVERSAL_TIME NODE_TRAVERSAL_TIME MY_ROUTE_TIMEOUT 6000 REV_ROUTE_LIFE RREP_WAIT_TIME Perkins, Royer Expires 20 April 1999 [Page 25] Internet Draft AODV 20 November 1998 RREP_WAIT_TIME 3 * NODE_TRAVERSAL_TIME * NET_DIAMETER / 2 RREQ_RETRIES 2 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 stretch across the network at its widest point. 14. Security Considerations Currently, AODV does not specify any special security measures. Route protocols, however, are prime targets for impersonation attacks, and must be protected by use of authentication techniques involving generation of unforgeable and cryptographically strong message digests or digital signatures. It is expected that, in environments where security is an issue, that IPSec authentication headers will be deployed along with the necessary key management to distribute keys to the members of the ad hoc network using AODV. Perkins, Royer Expires 20 April 1999 [Page 26] Internet Draft AODV 20 November 1998 References [1] S. Bradner. Key Words for Use in RFCs to Indicate Requirement Levels. RFC 2119, March 1997. [2] Charles E. Perkins. Terminology for Ad-Hoc Networking. draft-ietf-manet-terms-00.txt, November 1997. (work in progress). Author's Address Questions about this memo can be directed to: Charles E. Perkins Networking and Security Center Sun Microsystems Laboratories 901 San Antonio Rd. Palo Alto, CA 94303 USA +1 650 786 6464 +1 650 786 6445 (fax) 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 Perkins, Royer Expires 20 April 1999 [Page 27]