| Mobile Ad hoc Networks Working Group | C.E. Perkins |
| Internet-Draft | I.D. Chakeres |
| Intended status: Standards Track | CenGen |
| Expires: September 11, 2012 | March 12, 2012 |
Dynamic MANET On-demand (AODVv2) Routing
draft-ietf-manet-dymo-22
The Dynamic MANET On-demand (AODVv2) routing protocol is intended for use by mobile routers in wireless, multihop networks. AODVv2 determines unicast routes among AODVv2 routers within the network in an on-demand fashion, offering on-demand convergence in dynamic topologies.
This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/.
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."
This Internet-Draft will expire on September 11, 2012.
Copyright (c) 2012 IETF Trust and the persons identified as the document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License.
The Dynamic MANET On-demand (AODVv2) routing protocol enables on-demand, multihop unicast routing among participating AODVv2 routers. The basic operations of the AODVv2 protocol are route discovery and route maintenance. Route discovery is performed when an AODVv2 router receives a packet from a node under its responsibility to a destination for which it does not have a route. Route maintenance is performed to help ensure that the route being used to forward packets from the source to the destination remains operational.
During route discovery, the originator's AODVv2 router initiates dissemination of a Route Request (RREQ) throughout the network to find a route to a particular destination, via the AODVv2 router responsible for this destination. During this hop-by-hop dissemination process, each intermediate AODVv2 router records a route to the originator. When the target's AODVv2 router receives the RREQ, it responds with a Route Reply (RREP) sent hop-by-hop toward the originating AODVv2 router. Each intermediate AODVv2 router that receives the RREP creates a route to the target, and then the RREP is unicast hop-by-hop toward the originator. When the originator's AODVv2 router receives the RREP, routes have then been established between the originating AODVv2 router and the target AODVv2 router in both directions.
Route maintenance consists of two operations. In order to preserve routes in use, AODVv2 routers extend route lifetimes upon successfully forwarding a packet. In order to react to changes in the network topology, AODVv2 routers monitor traffic being forwarded. When a data packet is received for forwarding and a route for the destination is not known or the route is broken, then the AODVv2 router of the source of the packet is notified. A Route Error (RERR) is sent toward the packet source to indicate the route to particular destination addresses is invalid or missing. When the source's AODVv2 router receives the RERR, it deletes the route. If this source's AODVv2 router later receives a packet for forwarding to the same destination, it will need to perform route discovery again for that destination.
AODVv2 uses sequence numbers to ensure loop freedom [Perkins99]. Sequence numbers enable AODVv2 routers to determine the temporal order of AODVv2 route discovery messages, thereby avoiding use of stale routing information.
The AODVv2 routing protocol is designed for stub or disconnected mobile ad hoc networks (MANETs). AODVv2 handles a wide variety of mobility patterns by dynamically determining routes on-demand. AODVv2 also handles a wide variety of traffic patterns. In networks with a large number of routers, AODVv2 is best suited for sparse traffic scenarios where routers forward packets to only a small portion of the other AODVv2 routers, due to the on-demand nature of route discovery and route maintenance.
AODVv2 is applicable to memory constrained devices, since little routing state is maintained in each AODVv2 router. Only routing information related to active sources and destinations is maintained, in contrast to most proactive routing protocols that require routing information to all routers within the routing region be maintained.
AODVv2 supports routers with multiple interfaces participating in the MANET. AODVv2 routers can also perform routing on behalf of other nodes, attached via participating or non-participating interfaces.
AODVv2 routers perform route discovery to find a route to a particular destination. Therefore, AODVv2 routers MUST be configured to initiate and respond to route discovery on behalf of certain nodes, identified by address. When AODVv2 is the only protocol interacting with the forwarding table, AODVv2 MAY be configured to perform route discovery for all unknown unicast destinations.
At any time within an AODVv2 routing region, only one AODVv2 router SHOULD be responsible for, i.e. "own", any particular address. Coordination among multiple AODVv2 routers to distribute routing information correctly for a shared address (i.e. an address that is advertised and can be reached via multiple AODVv2 routers) is not described in this document. The router behavior for shifting responsibility for an address from one AODVv2 router to another is mentioned in Appendix Appendix C.
AODVv2 only utilizes bidirectional links. In the case of possible unidirectional links, either blacklists (see Section 7.2) or other means (e.g. adjacency establishment with only neighboring routers that have bidirectional communication as indicated by NHDP [I-D.ietf-manet-nhdp]) of ensuring and monitoring bi-directionality is recommended. Otherwise, persistent packet loss may occur.
The routing algorithm in AODVv2 may be operated at layers other than the network layer, using layer-appropriate addresses.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119].
Additionally, this document uses some terminology from [RFC5444].
This document defines the following terminology:
The route table entry is a conceptual data structure. Implementations may use any internal representation that conforms to the semantics of a route as specified in this document.
Conceptually, a route table entry has the following fields:
The following field is optional:
Not including optional information may cause performance degradation, but it will not cause the protocol to operate incorrectly.
In addition to a route table data structure, each route table entry may have several timers associated with the information. These timers/timeouts are discussed in Section 5.2.3.
When describing AODVv2 protocol messages, it is necessary to refer to fields in several distinct parts of the overall packet. These locations include the IP header, the UDP header, and fields from [RFC5444]. This document uses the following notation conventions. Information found in the table.
| Information Location | Notational Prefix |
|---|---|
| IP header | IP. |
| UDP header | UDP. |
| RFC5444 message header | MsgHdr. |
| RFC5444 message TLV | MsgTLV. |
| RFC5444 address blocks | AddBlk. |
| RFC5444 address block TLV | AddTLV. |
AODVv2 messages conform to the generalized packet and message format as described in [RFC5444]. Here is a brief description of the format. A packet is made up of messages. A message is made up of a message header, message TLV block, and zero or more address blocks. Each of the address blocks may also have an associated address TLV block.
For interoperability with other AODVv2 routers, all AODVv2 messages specified in this document SHOULD sent using the IP protocol number (138) reserved for manet protocols [RFC5498]; or the UDP destination port (269) reserved for manet protocols [RFC5498] and IP protocol number for UDP.
Most AODVv2 messages are sent with the IP destination address set to the link-local multicast address LL-MANET-Routers [RFC5498] unless otherwise stated. Therefore, all AODVv2 routers SHOULD subscribe to LL-MANET-Routers [RFC5498] for receiving control packets. Note that multicast packets MAY be sent via unicast. For example, this may occur for certain link-types (non broadcast mediums), improved robustness, or manually configured router adjacencies.
Unicast AODVv2 messages (e.g. RREP) unless otherwise specified in this document are sent with the IP destination set to the Route.NextHopAddress of the route to the TargetNode.
The IPv4 TTL (IPv6 Hop Limit) field for all packets containing AODVv2 messages is set to 255. If a packet is received with a value other than 255, it is discarded. This mechanism helps to ensures that packets have not passed through any intermediate routers, and it is known as GTSM [RFC5082].
The length of an address (32 bits for IPv4 and 128 bits for IPv6) inside an AODVv2 message depends on the msg-addr-length (MAL) in the msg-header, as specified in [RFC5444].
AODVv2 control packets SHOULD be given priority queuing and channel access.
Routing Messages (RteMsgs) are used to disseminate routing information. There are two AODVv2 message types that are considered to be routing messages (RteMsgs): RREQ and RREP. They contain very similar information and function, but have slightly different handling rules. The main difference between the two messages is that RREQ messages generally solicit a RREP, whereas a RREP is the response to RREQ.
RteMsg creation and handling are described in Section 5.3.
A RteMsg requires the following information:
A RteMsg may optionally include the following information:
A RERR message is used to disseminate the information that a route is not available for one or more particular addresses.
RERR creation and handling are described in Section 5.5.
A RERR requires the following information:
A Route Error may optionally include the following information:
AODVv2 sequence numbers allow AODVv2 routers to judge the freshness of routing information and ensure loop freedom.
AODVv2 requires that each AODVv2 router in the network maintain its own AODVv2 sequence number (OwnSeqNum) on behalf of the addresses for which it is responsible. OwnSeqNum a 16-bit unsigned integer. The circumstances for ThisNode to increment its OwnSeqNum are described in Section 5.3.
When ThisNode increments its OwnSeqNum it MUST do so by treating the sequence number value as an unsigned number.
Incrementing an OwnSeqNum whose value is the largest largest possible number representable as a 16-bit unsigned integer (i.e., 65,535), SHOULD be set to one (1). In other words, the sequence number after 65,535 is 1.
An AODVv2 router SHOULD maintain its sequence number in persistent storage.
If an AODVv2 router's OwnSeqNum is lost, it MUST take certain actions to avoid creating routing loops. To prevent this possibility after OwnSeqNum loss an AODVv2 router MUST wait for at least ROUTE_DELETE_TIMEOUT before fully participating in the AODVv2 routing protocol. If an AODVv2 control message is received during this waiting period, the AODVv2 router SHOULD handle it normally but MUST NOT transmit or retransmit any AODVv2 messages. If a data packet is received for forwarding to another destination during this waiting period, the AODVv2 router MUST generate a RERR message indicating that this route is not available and reset its waiting timeout. At the end of the waiting period the AODVv2 router sets its OwnSeqNum to one (1) and begins participating.
The longest a node need wait is ROUTE_SEQNUM_AGE_MAX_TIMEOUT. At the end of the maximum waiting period a node SHOULD set its OwnSeqNum to one (1) and begins participating.
(Node.SeqNum - Route.SeqNum < 0)
using signed 16-bit arithmetic
(Node.SeqNum == Route.SeqNum) AND
((Node.Dist is unknown) OR
(Route.Dist is unknown) OR
(Node.Dist > Route.Dist + 1))
((Node.SeqNum == Route.SeqNum) AND
(((Node.Dist == Route.Dist + 1) AND (Route.Broken == false)) OR
((Node.Dist == Route.Dist) AND
(RteMsg is RREQ) AND (Route.Broken == false))))
(Node.SeqNum - Route.SeqNum > 0) OR
using signed 16-bit arithmetic
((Node.SeqNum == Route.SeqNum) AND
((Node.Dist < Route.Dist) OR
((Node.Dist == Route.Dist + 1) AND (Route.Broken == true)) OR
((Node.Dist == Route.Dist) AND
((RteMsg is RREP) OR (Route.Broken == true)))))
Given a route table entry (Route.SeqNum, Route.Dist, and Route.Broken) and new incoming routing information for a particular node in a RteMsg (Node.SeqNum, Node.Dist, and RteMsg message type - RREQ/RREP), the quality of the new routing information is evaluated to determine its usefulness. Incoming routing information is classified as follows:
The route table entry is populated with the following information:
Fields without known values are not populated with any value.
The timer for the minimum delete timeout (ROUTE_AGE_MIN) is set to ROUTE_AGE_MIN_TIMEOUT. The timer for the maximum delete timeout (ROUTE_SEQNUM_AGE_MAX) is set to Node.AddTLV.VALIDITY_TIME [RFC5497] if included; otherwise, ROUTE_SEQNUM_AGE_MAX is set to ROUTE_SEQNUM_AGE_MAX_TIMEOUT. The usage of these timers and others are described in Section 5.2.3.
At this point, a forwarding route has been created and the Route.Forwarding flag set. Afterward, the route can be used to send any queued data packets and forward any incoming data packets for Route.Address. This route also fulfills any outstanding route discovery attempts for Node.Address.
When an AODVv2 router transmits a RteMsg, other AODVv2 routers expect the transmitting AODVv2 router to have a forwarding route to the RteMsg originator. After updating a route table entry, it SHOULD be maintained for at least ROUTE_AGE_MIN. Failure to maintain the information might result in lost messages/packets, or in the worst case scenario several duplicate messages.
After the ROUTE_AGE_MIN timeout a route can safely be deleted.
Sequence number information is time sensitive, and MUST be deleted after a time in order to ensure loop-free routing.
After the ROUTE_SEQNUM_AGE_MAX timeout a route's sequence number information MUST be discarded.
When a route is used to forward data packets, this timer is set to expire after ROUTE_USED_TIMEOUT. This operation is also discussed in Section 5.5.2.
If a route has not been used recently, then a timer for ROUTE_DELETE is set to ROUTE_DELETE_TIMEOUT.
As time progresses the likelihood that old routing information is useful decreases, especially if the network nodes are mobile. Therefore, old information SHOULD be deleted.
After the ROUTE_DELETE timeout if a forwarding route exists it SHOULD be removed, and the routing table entry SHOULD also be deleted.
Before an AODVv2 router creates a RREQ it SHOULD increment its OwnSeqNum by one (1) according to the rules specified in Section 5.1. Incrementing OwnSeqNum will ensure that all nodes with existing routing information will consider this new information preferable to existing routing table information. If the sequence number is not incremented, certain AODVv2 routers might not consider this information preferable, if they have existing better routing information.
First, ThisNode adds the AddBlk.TargetNode.Address to the RREQ; the unicast IP Destination Address for which a forwarding route does not exist.
If a previous value of the TargetNode.SeqNum is known (from a routing table entry using longest-prefix matching), it SHOULD be placed in TargetNode.AddTLV.SeqNum in all but the last RREQ attempt. If a TargetNode.SeqNum is not included, it is assumed to be unknown by handling nodes. This operation ensures that no intermediate AODVv2 routers reply, and ensures that the TargetNode's AODVv2 router increments its sequence number.
Next, the node adds AddBlk.OrigNode.Address, its prefix, and the OrigNode.AddTLV.SeqNum (OwnSeqNum) to the RteMsg.
The OrigNode.Address is the address of the source for which this AODVv2 router is initiating this route discovery. The OrigNode.Address MUST be a unicast address. This information will be used by nodes to create a route toward the OrigNode, enabling delivery of a RREP, and eventually used for proper forwarding of data packets.
If OrigNode.Dist is included it is set to a number greater than zero (0).
The MsgHdr.HopLimit SHOULD be set to MSG_HOPLIMIT.
For RREQ, the MsgHdr.HopLimit MAY be set in accordance with an expanding ring search as described in [RFC3561] to limit the RREQ propagation to a subset of the local network and possibly reduce route discovery overhead.
The IP.DestinationAddress for multicast RREQ is set to LL-MANET-Routers. For links that do not support multicast or situations in which unicast messaging is preferred, the IP.DestinationAddress for unicast RREQ is set to the NextHopAddress.
First, the AddBlk.TargetNode.Address is added to the RREP. The TargetNode is the ultimate destination of this RREP; the RREQ OrigNode.Address.
Next, AddBlk.OrigNode.Address and prefix are added to the RREP. The AddBlk.OrigNode.Address is the RREQ TargetNode.Address. The AddBlk.OrigNode.Address MUST be a unicast IP address. ThisNode SHOULD advertise the largest known prefix containing AddBlk.OrigNode.Address.
When the RteMsg TargetNode's AODVv2 router creates a RREP, if the TargetNode.SeqNum was not included in the RREQ, ThisNode MUST increment its OwnSeqNum by one (1) according to the rules specified in Section 5.1.
If TargetNode.SeqNum was included in the RteMsg and TargetNode.SeqNum - OwnSeqNum < 0 (using signed 16-bit arithmetic), OwnSeqNum SHOULD be incremented by one (1) according to the rules specified in Section 5.1.
If TargetNode.SeqNum is included in the RteMsg and TargetNode.SeqNum == OwnSeqNum (using signed 16-bit arithmetic) and OrigNode.Dist will not be included in the RREP being generated, OwnSeqNum SHOULD be incremented by one (1) according to the rules specified in Section 5.1.
If OwnSeqNum is not incremented the routing information might be considered stale. In this case, the RREP might not reach the RREP Target.
After any of the sequence number operations above, the RREP OrigNode.AddTLV.SeqNum (OwnSeqNum) MUST also be added to the RREP.
Other AddTLVs in the RREP for the OrigNode and TargetNode SHOULD be included and set accordingly. If OrigNode.Dist is included it is set to a number greater than zero (0) and less than or equal to 65,535. The Distance value will influence judgment of the routing information (Section 5.2.1) against known information at other AODVv2 routers that handle this RteMsg.
The MsgHdr.HopLimit is set to MSG_HOPLIMIT.
The IP.DestinationAddress for RREP is set to the IP address of the Route.NextHopAddress for the route to the RREP TargetNode.
First, ThisNode examines the RteMsg to ensure that it contains the required information: MsgHdr.HopLimit, AddBlk.TargetNode.Address, AddBlk.OrigNode.Address, and OrigNode.AddTLV.SeqNum. If the required information do not exist, the message is discarded and further processing stopped.
Next, ThisNode MAY selectively attend to messages based upon information in the message. ThisNode SHOULD only handle messages from adjacent AODVv2 routers. If ThisNode chooses not to handle this message, the message is discarded and further processing stopped.
ThisNode checks if the AddBlk.OrigNode.Address is a valid multihop-capable (e.g. site or global scope) unicast address. If the address is not a valid unicast address, the message is discarded and further processing stopped.
ThisNode also checks whether AddBlk.OrigNode.Address is an address handled by this AODVv2 router. If this node is the originating AODVv2 router, the RteMsg is dropped.
ThisNode checks if the AddBlk.TargetNode.Address is a valid multihop-capable unicast address. If the address is not a valid unicast address, the message is discarded and further processing stopped.
Next, ThisNode checks whether its routing table has an entry to the AddBlk.OrigNode.Address using longest-prefix matching [RFC1812]. If a route with a valid Route.SeqNum does not exist, then the new routing information is considered preferable and a new route table entry is created and updated as described in Section 5.2.2. If a route table entry does exists and it has a known Route.SeqNum, the incoming routing information is compared with the route table entry following the procedure described in Section 5.2.1. If the incoming routing information is considered preferable, the route table entry is updated as described in Section 5.2.2.
For each address (except the TargetNode) in the RteMsg that includes AddTLV.Dist information, the AddTLV.Dist information MAY be incremented. If the resulting Distance value for the OrigNode is greater than 65,535, the message is discarded. If the resulting Distance value for another node is greater than 65,535, the associated address and its information are removed from the RteMsg. The updated Distance value will influence judgment of the routing information (Section 5.2.1).
After handling the OrigNode's routing information, then each address that is not the TargetNode MAY be considered for creating and updating routes. Creating and updating routes to other nodes can eliminate RREQ for those IP destinations, in the event that data needs to be forwarded to the IP destination(s) now or in the near future.
For each of the additional addresses considered, ThisNode first checks the that the address is a multihop-capable unicast address. If the address is not a unicast address, the address and all related information MUST be removed.
If the routing table does not have a matching route with a known Route.SeqNum for this additional address using longest-prefix matching, then a route is created and updated as described in Section 5.2.2. If a route table entry exists with a known Route.SeqNum, the incoming routing information is compared with the route table entry following the procedure described in Section 5.2.1. If the incoming routing information is considered preferable, the route table entry is updated as described in Section 5.2.2.
If the routing information for an AdditionalNode.Address is not considered preferable, then it is removed from the RteMsg. Removing this information ensures that the information is not propagated.
At this point, if the routing information for the OrigNode was not preferable then this RteMsg SHOULD be discarded and no further processing of this message SHOULD be performed.
If the ThisNode is the AODVv2 router responsible for the TargetNode and this RteMsg is a RREQ, then ThisNode responds with a RREP to the RREQ OrigNode (the new RREP's TargetNode). The procedure for issuing a new RREP is described in Section 5.3.2. At this point, ThisNode need not perform any more operations for the RteMsg being processed.
As an alternative to issuing a RREP, ThisNode MAY choose to distribute routing information about ThisNode (the RREQ TargetNode) more widely. That is, ThisNode MAY optionally perform a route discovery; by issuing a RREQ with ThisNode listed as the TargetNode, using the procedure in Section 5.3.1. At this point, ThisNode need not perform any more operations for the RteMsg being processed.
If the resulting Distance value for the OrigNode is greater than 65,535, the message is discarded. If the resulting Distance value for another node is greater than 65,535, the associated address and its information are removed from the RteMsg.
Next, the MsgHdr.HopLimit is decremented by one (1). If this RteMsg's MsgHdr.HopLimit is greater than or equal to one (1), ThisNode is not the TargetNode, AND this RteMsg is a RREQ, then the current RteMsg (altered by the procedure defined above) SHOULD be sent to the IP.DestinationAddress LL-MANET-Routers [RFC5498]. If the RREQ is unicast, the IP.DestinationAddress is set to the NextHopAddress.
If this RteMsg's MsgHdr.HopLimit is greater than or equal to one (1), ThisNode is not the TargetNode, AND this RteMsg is a RREP, then the current RteMsg is sent to the Route.NextHopAddress for the RREP's TargetNode.Address. If no forwarding route exists to TargetNode.Address, then a RERR SHOULD be issued to the OrigNode of the RREP.
By sending the updated RteMsg, ThisNode advertises that it will route for addresses contained in the outgoing RteMsg based on the information enclosed. ThisNode MAY choose not to send the RteMsg, though not resending this RteMsg could decrease connectivity in the network or result in a non-shortest distance path.
Some examples of why ThisNode might choose to not re-issue a RteMsg are: if ThisNode does not want to advertise routing for the contained addresses because it is already heavily loaded; if ThisNode has already issued nearly identical routing information (e.g. ThisNode had recently issued a RteMsg with nearly the same distance); or if ThisNode is low on energy and does not want to expend energy for control message sending or packet forwarding. The exact circumstances producing such behavior are not specified in this document.
When a source's AODVv2 router needs to forward a data packet on behalf of an attached node and it does not have a forwarding route to the data packet's unicast IP destination address, ThisNode sends a RREQ (described in Section 5.3.1) to discover a route to the particular destination (TargetNode).
After issuing a RREQ, the OrigNode AODVv2 router waits for a route to be created to the TargetNode. If a route is not created within RREQ_WAIT_TIME, ThisNode may again try to discover a route by issuing another RREQ using the procedure defined in Section 5.3.1 again. Route discovery SHOULD be considered failed after DISCOVERY_ATTEMPTS_MAX and the final RREQ's corresponding RREQ_WAIT_TIME.
To reduce congestion in a network, repeated attempts at route discovery for a particular TargetNode SHOULD utilize an exponential backoff.
For example, the first time an AODVv2 router issues a RREQ, it waits RREQ_WAIT_TIME for a route to the TargetNode. If a route is not found within that time, the AODVv2 router MAY send another RREQ. If a route is not found within two (2) times the current waiting time, another RREQ MAY be sent. No more than DISCOVERY_ATTEMPTS_MAX route discovery attempts SHOULD be made before considering route discovery for this destination to have failed. For each additional attempt, the waiting time for the previous RREQ is multiplied by two (2) so that the waiting time conforms to a binary exponential backoff.
Data packets awaiting a route SHOULD be buffered by the source's AODVv2 router. This buffer SHOULD have a fixed limited size (BUFFER_SIZE_PACKETS or BUFFER_SIZE_BYTES) and older data packets SHOULD be discarded first.
Buffering of data packets can have both positive and negative effects, and therefore buffer settings (BUFFER_DURING_DISCOVERY) SHOULD be administratively configurable or intelligently controlled.
If a route discovery attempt has failed (i.e. an attempt or multiple attempts have been made without receiving a RREP) to find a route to the TargetNode, any data packets buffered for the corresponding TargetNode are dropped and a Destination Unreachable ICMP message SHOULD be delivered to the source.
A RERR SHOULD be issued if a data packet is to be forwarded and it cannot be delivered to the next-hop because no forwarding route for the IP.DestinationAddress exists; RERR generation is described in Section 5.5.3.
Upon this condition, an ICMP Destination Unreachable message SHOULD NOT be generated unless this router is responsible for the IP.DestinationAddress and that IP.DestinationAddress is known to be unreachable.
In addition to inability to forward a data packet, a RERR SHOULD be issued immediately after detecting a broken link (see Section 5.5.1) of a forwarding route to quickly notify AODVv2 routers that certain routes are no longer available. If a newly unavailable route has not been used recently (indicated by ROUTE_USED), the RERR SHOULD NOT be generated.
Nodes MUST monitor connectivity to adjacent next-hop AODVv2 routers on forwarding routes. This monitoring can be accomplished by one or several mechanisms, including:
Upon determining that a next-hop AODVv2 router is unreachable, ThisNode MUST remove the affected forwarding routes (those with an unreachable next-hop) and unset the Route.Forwarding flag. ThisNode also flags the associated routes in AODVv2's routing table as Broken. For each broken route the timer for ROUTE_DELETE is set to ROUTE_DELETE_TIMEOUT.
To avoid removing the forwarding route to reach the IP.SourceAddress, ThisNode SHOULD set the "ROUTE_USED" timeout to the value ROUTE_USED_TIMEOUT for the route to the IP.SourceAddress upon receiving a data packet. If the timer for ROUTE_DELETE is set, it is removed.
To avoid removing the forwarding route to the IP.DestinationAddress that is being used, ThisNode SHOULD set the "ROUTE_USED" timeout to the value ROUTE_USED_TIMEOUT for the route to the IP.DestinationAddress upon sending a data packet. If the timer for ROUTE_DELETE is set, it is removed.
A RERR informs AODVv2 routers that a route to certain destinations is not available through ThisNode.
When creating a new RERR, the address of the first UnreachableNode (IP.DestinationAddress from a data packet or RREP.TargetNode.Address) is inserted into an Address Block AddBlk.UnreachableNode.Address. If a prefix is known for the UnreachableNode.Address, it SHOULD be included. Otherwise, the UnreachableNode.Address is assumed to be a host address with a full length prefix. If a value for the UnreachableNode's SeqNum (UnreachableNode.AddTLV.SeqNum) is known, it SHOULD be placed in the RERR. The MsgHdr.HopLimit is set to MSG_HOPLIMIT.
If SeqNum information is not known or not included in the RERR, all nodes handling the RERR will assume their routing information associated with the UnreachableNode is no longer valid and flag those routes as broken.
A multicast RERR is sent to the IP.DestinationAddress LL-MANET-Routers [RFC5498]. Sending the RERR to the LL-MANET-Routers address notifies all nearby AODVv2 routers that might depend on the now broken link. If the RERR is unicast, the IP.DestinationAddress is set to the NextHopAddress.
At this point, the packet or message that forced generation of this RERR SHOULD be discarded.
First, ThisNode examines the RteMsg to ensure that it contains the required information: MsgHdr.HopLimit and AddBlk.UnreachableNode.Address. If the required information do not exist, the message is discarded and further processing stopped.
Next, ThisNode MAY selectively handle messages based upon information in the message. ThisNode MAY choose to only handle messages from adjacent AODVv2 routers. If ThisNode chooses not to handle this message, the message is discarded and further processing stopped.
When an AODVv2 router handles a RERR, it examines each UnreachableNode's information. The attending AODVv2 router removes the forwarding route, unsets the Route.Forwarding flag, sets the Route.Broken flag, and the timer for ROUTE_DELETE is set to ROUTE_DELETE_TIMEOUT for each UnreachableNode.Address found using longest prefix matching that meets all of the following conditions:
During handling if Route.SeqNum is zero (0) or unknown and UnreachableNode.SeqNum exists in the RERR and is not zero (0), then Route.SeqNum MAY be set to UnreachableNode.SeqNum. Setting Route.SeqNum can reduce future RERR handling and forwarding.
Each UnreachableNode that did not result in a broken route is removed from the RERR, since propagation of this information will not result in any benefit.
Each UnreachableNode that did result in a broken route SHOULD remain in the RERR.
If any UnreachableNode was removed, all other information (AddTLVs) associated with the removed address(es) MUST also be removed.
After handling if Route.SeqNum is known and an UnreachableNode.SeqNum is not included in the RERR, then Route.SeqNum (i.e. UnreachableNode.SeqNum) MAY be added to the RERR. Including UnreachableNode.SeqNum can reduce future RERR handling and forwarding.
If no UnreachableNode addresses remain in the RERR, no other handling is required and the RERR is discarded.
If handling continues, the MsgHdr.HopLimit is decremented by one (1). Further, if this RERR's new MsgHdr.HopLimit is greater than one (1) and at least one unreachable node address remains in the RERR, then the updated RERR SHOULD be sent.
A multicast RERR is sent to the IP.DestinationAddress LL-MANET-Routers [RFC5498]. If the RERR is unicast, the IP.DestinationAddress is set to the NextHopAddress.
If a message with an unknown type is received, the message is discarded.
For handling of messages that contain unknown TLV types, the default behavior is to leave the information in control messages unmodified. Although, this behavior (UNKNOWN_TYPES) MAY be administratively controlled.
AODVv2 routers specify the prefix length for each advertised address. Any nodes (other than the advertising AODVv2 router) within the advertised prefix MUST NOT participate in the AODVv2 protocol directly. For example, advertising 192.0.2.1 with a prefix length of 24 indicates that all nodes with the matching 192.0.2.X are reachable through this AODVv2 router.
Simple Internet attachment consists of a stub network of AODVv2 routers connected to the Internet via a single Internet AODVv2 router (IDR).
AODVv2 routers, and hosts behind these routers, wishing to be reachable from hosts on the Internet MUST have IP addresses within the IDR's routable and topologically correct prefix (e.g. 192.0.2.0/24).
The IDR is responsible for generating RREQ to find nodes within the AODVv2 Region on behalf of nodes on the Internet, as well as responding to route requests from the AODVv2 region on behalf of the nodes on the Internet.
/--------------------------\
/ Internet \
\ /
\------------+-------------/
|
Routable & |
Topologically |
Correct |
Prefix |
+-----+------+
| Internet |
/------| AODVv2 |-------\
/ | Router | \
/ |192.0.2.1/32| \
| |Responsible | |
| | for | |
| |AODVv2 Region | |
| |192.0.2.0/24| |
| +------------+ |
| +--------------+ |
| | AODVv2 Router | |
| | 192.0.2.2/32 | |
| +--------------+ |
| +--------------+ |
| | AODVv2 Router | |
| | 192.0.2.3/32 | |
\ +--------------+ /
\ /
\---------------------------/
When an AODVv2 router within the AODVv2 Region wants to discover a route to a node on the Internet, it uses the normal AODVv2 route discovery for that IP Destination Address. The IDR is responsible for properly responding to RREQ on behalf of the Internet destination.
When a packet from a node on the Internet destined for a node in the AODVv2 region reaches the IDR, if the IDR does not have a route to that destination it will perform normal AODVv2 route discovery for that destination.
AODVv2 may be used with multiple interfaces; therefore, the particular interface over which packets arrive MUST be known whenever a packet is received. Whenever a new route is created, the interface through which the Route.Address can be reached is also recorded in the route table entry.
When multiple interfaces are available, a node transmitting a multicast packet with IP.DestinationAddress set to LL-MANET-Routers SHOULD send the packet on all interfaces that have been configured for AODVv2 operation.
Similarly, AODVv2 routers should subscribe to LL-MANET-Routers on all their AODVv2 interfaces.
To ensure predictable control overhead, AODVv2 router's rate of packet/message generation SHOULD be limited. The rate and algorithm for limiting messages (CONTROL_TRAFFIC_LIMITS) is left to the implementor and should be administratively configurable or intelligently controlled. AODVv2 control messages SHOULD be discarded in the following order of preference: RREQ, RREP, and finally RERR.
AODVv2 contains several parameters which MUST be administratively configured. The list of these follows:
Required Administratively Configured Parameters
| Name | Description |
|---|---|
| RESPONSIBLE_ADDRESSES | List of addresses or routing prefixes, for which this AODVv2 router is responsible. If, RESPONSIBLE_ADDRESSES is zero, this AODVv2 router is only responsible for its own addresses. |
| AODVv2_INTERFACES | List of the interfaces participating in AODVv2 routing protocol. |
AODVv2 contains a number of timers. The default timing parameter values follow:
Default Timing Parameter Values
| Name | Value |
|---|---|
| ROUTE_TIMEOUT | 5 seconds |
| ROUTE_AGE_MIN_TIMEOUT | 1 second |
| ROUTE_SEQNUM_AGE_MAX_TIMEOUT | 60 seconds |
| ROUTE_USED_TIMEOUT | ROUTE_TIMEOUT |
| ROUTE_DELETE_TIMEOUT | 2 * ROUTE_TIMEOUT |
| ROUTE_RREQ_WAIT_TIME | 2 seconds |
| UNICAST_MESSAGE_SENT_TIMEOUT | 1 second |
The above timing parameter values work well for small and medium well-connected networks with moderate topology changes.
The timing parameters SHOULD be administratively configurable for the network where AODVv2 is used. Ideally, for networks with frequent topology changes the AODVv2 parameters should be adjusted using either experimentally determined values or dynamic adaptation. For example, in networks with infrequent topology changes ROUTE_USED_TIMEOUT may be set to a much larger value.
Default Parameter Values
| Name | Value | Description |
|---|---|---|
| MSG_HOPLIMIT | 10 hops | This value MUST be larger than the AODVv2 network diameter. Otherwise, routing messages may not reach their intended destinations. |
| DISCOVERY_ATTEMPTS_MAX | 3 | The number of route discovery attempts to make before indicating that a particular address is not reachable. |
In addition to the above parameters and timing values, several administrative options exist. These options have no influence on correct routing behavior, although they may potentially reduce AODVv2 routing control messaging in certain situations. The default behavior is to NOT enable any of these options; and although many of these options can be administratively controlled, they may be better served by intelligent control. The following table enumerates several of the options.
Administratively Controlled Options
| Name | Description |
|---|---|
| BUFFER_DURING_DISCOVERY | Whether and how much data to buffer during route discovery. |
| UNKNOWN_TYPES | What action to take when an unknown TLV type is received. The default action is to forward this information unmodified. Another action would be to remove this information. |
| CONTROL_TRAFFIC_LIMITS | AODVv2 control messaging SHOULD be limited to avoid consuming all the network bandwidth. |
Note: several fields have limited size (bits or bytes) these sizes and their encoding may place specific limitations on the values that can be set. For example, MsgHdr.HopLimit is a 8-bit field and therefore MSG_HOPLIMIT cannot be larger than 255.
In its default mode of operation, AODVv2 uses the UDP port MANET [RFC5498] to carry protocol packets. AODVv2 also uses the link-local multicast address LL-MANET-Routers [RFC5498].
This section specifies several message types, message tlv-types, and address tlv-types.
AODVv2 Message Types
| Name | Type |
|---|---|
| Route Request (RREQ) | 10 - TBD |
| Route Reply (RREP) | 11 - TBD |
| Route Error (RERR) | 12 - TBD |
Message TLV Types
| Name | Type | Length | Value |
|---|---|---|---|
| Unicast Response Request | 10 - TBD | 0 octets | Indicates to the processing node that the previous hop (IP.SourceAddress) expects a unicast message within UNICAST_MESSAGE_SENT_TIMEOUT. Any unicast packet will serve this purpose, and it MAY be an ICMP REPLY message. If a message is not sent, then the previous hop can assume that the link is unidirectional and MAY blacklist the link to this node. |
Address Block TLV Types
| Name | Type | Length | Value |
|---|---|---|---|
| AODVv2 Sequence Number (AODVv2SeqNum) | 10 - TBD | up to 2 octets | The AODVv2 sequence num associated with this address. The sequence number may be the last known sequence number. |
| Distance | 11 - TBD | up to 2 octets | A metric of the distance traversed by the information associated with this address. |
| VALIDITY_TIME | 1[RFC5497] | The maximum amount of time that information can be maintained before being deleted. The VALIDITY_TIME TLV is defined in [RFC5497]. |
The objective of the AODVv2 protocol is for each router to communicate reachability information to addresses for which it is responsible. Positive routing information (i.e. a route exists) is distributed via RteMsgs and negative routing information (i.e. a route does not exist) via RERRs. AODVv2 routers that handle these messages store the contained information to properly forward data packets, and they generally provide this information to other AODVv2 routers.
This section does not mandate any specific security measures. Instead, this section describes various security considerations and potential avenues to secure AODVv2 routing.
The most important security mechanisms for AODVv2 routing are integrity/authentication and confidentiality.
In situations where routing information or router identity are suspect, integrity and authentication techniques SHOULD be applied to AODVv2 messages. In these situations, routing information that is distributed over multiple hops SHOULD also verify the integrity and identity of information based on originator of the routing information.
A digital signature could be used to identify the source of AODVv2 messages and information, along with its authenticity. A nonce or timestamp SHOULD also be used to protect against replay attacks. S/MIME and OpenPGP are two authentication/integrity protocols that could be adapted for this purpose.
In situations where confidentiality of AODVv2 messages is important, cryptographic techniques can be applied.
In certain situations, like sending a RREP or RERR, an AODVv2 router could include proof that it has previously received valid routing information to reach the destination, at one point of time in the past. In situations where routers are suspected of transmitting maliciously erroneous information, the original routing information along with its security credentials SHOULD be included.
Note that if multicast is used, any confidentiality and integrity algorithms used must permit multiple receivers to handle the message.
AODVv2 is a descendant of the design of previous MANET on-demand protocols, especially AODV [RFC3561] and DSR [RFC4728]. Changes to previous MANET on-demand protocols stem from research and implementation experiences. Thanks to Elizabeth Belding-Royer for her long time authorship of AODVv2. Additional thanks to Luke Klein-Berndt, Pedro Ruiz, Fransisco Ros, Koojana Kuladinithi, Ramon Caceres, Thomas Clausen, Christopher Dearlove, Seung Yi, Romain Thouvenin, Tronje Krop, Henner Jakob, Alexandru Petrescu, Christoph Sommer, Cong Yuan, Lars Kristensen, and Derek Atkins for reviewing of AODVv2, as well as several specification suggestions.
Many good ideas from LOADng [I-D.clausen-lln-loadng] are shaping this evolution of the [manet] reactive routing protocol specification. Thanks are due to T. Clausen, A. Colin de Verdiere, J. Yi, A. Niktash, Y. Igarashi, SATOH. H., and U. Herberg for their development of LOADng and sharing details for ensuring appropriateness of AODVv2 for LLNs.
| [RFC1812] | Baker, F., "Requirements for IP Version 4 Routers", RFC 1812, June 1995. |
| [RFC2119] | Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. |
| [RFC5082] | Gill, V., Heasley, J., Meyer, D., Savola, P. and C. Pignataro, "The Generalized TTL Security Mechanism (GTSM)", RFC 5082, October 2007. |
| [RFC5444] | Clausen, T., Dearlove, C., Dean, J. and C. Adjih, "Generalized Mobile Ad Hoc Network (MANET) Packet/Message Format", RFC 5444, February 2009. |
| [RFC5497] | Clausen, T. and C. Dearlove, "Representing Multi-Value Time in Mobile Ad Hoc Networks (MANETs)", RFC 5497, March 2009. |
| [RFC5498] | Chakeres, I., "IANA Allocations for Mobile Ad Hoc Network (MANET) Protocols", RFC 5498, March 2009. |
| [RFC2328] | Moy, J., "OSPF Version 2", STD 54, RFC 2328, April 1998. |
| [RFC5340] | Coltun, R., Ferguson, D., Moy, J. and A. Lindem, "OSPF for IPv6", RFC 5340, July 2008. |
| [RFC3561] | Perkins, C., Belding-Royer, E. and S. Das, "Ad hoc On-Demand Distance Vector (AODV) Routing", RFC 3561, July 2003. |
| [RFC4728] | Johnson, D., Hu, Y. and D. Maltz, "The Dynamic Source Routing Protocol (DSR) for Mobile Ad Hoc Networks for IPv4", RFC 4728, February 2007. |
| [RFC4861] | Narten, T., Nordmark, E., Simpson, W. and H. Soliman, "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, September 2007. |
| [RFC5148] | Clausen, T., Dearlove, C. and B. Adamson, "Jitter Considerations in Mobile Ad Hoc Networks (MANETs)", RFC 5148, February 2008. |
| [Perkins99] | Perkins, C. and E. Belding-Royer, "Ad hoc On-Demand Distance Vector (AODV) Routing", Proceedings of the 2nd IEEE Workshop on Mobile Computing Systems and Applications, New Orleans, LA, pp. 90-100, February 1999. |
| [I-D.ietf-manet-nhdp] | Clausen, T, Dearlove, C and J Dean, "Mobile Ad Hoc Network (MANET) Neighborhood Discovery Protocol (NHDP)", Internet-Draft draft-ietf-manet-nhdp-15, December 2010. |
| [I-D.ietf-ospf-multi-instance] | Lindem, A, Roy, A and S Mirtorabi, "OSPF Multi-Instance Extensions", Internet-Draft draft-ietf-ospf-multi-instance-04, April 2011. |
| [I-D.chakeres-manet-manetid] | Chakeres, I, "MANET_ID TLV", Internet-Draft draft-chakeres-manet-manetid-03, February 2008. |
| [I-D.clausen-lln-loadng] | Clausen, T, Verdiere, A, Yi, J, Niktash, A, Igarashi, Y and U Herberg, "The LLN On-demand Ad hoc Distance-vector Routing Protocol - Next Generation (LOADng)", Internet-Draft draft-clausen-lln-loadng-01, October 2011. |
Only one AODVv2 router within a routing region SHOULD be responsible for a particular address at any time. If two AODVv2 routers dynamically pass responsibility of an address correct AODVv2 routing behavior must be observed. The AODVv2 router adding the new address must wait for any exiting routing information about this address to be purged from the network. Therefore, it must wait at least ROUTER_SEQNUM_AGE_MAX_TIMEOUT after the previous AODVv2 router for this address stopped participating and advertising routing information on its behalf.