Mobile Ad hoc Networks Working I. Chakeres Group Boeing Internet-Draft C. Perkins Expires: September 6, 2006 Nokia March 5, 2006 Dynamic MANET On-demand (DYMO) Routing draft-ietf-manet-dymo-04 Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. 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." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on September 6, 2006. Copyright Notice Copyright (C) The Internet Society (2006). Abstract The Dynamic MANET On-demand (DYMO) routing protocol is intended for use by mobile nodes in wireless multihop networks. It offers adaptation to changing network topology and determines unicast routes between nodes within the network on-demand. Chakeres & Perkins Expires September 6, 2006 [Page 1] Internet-Draft DYMO March 2006 Table of Contents 1. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5 3. Data Structures . . . . . . . . . . . . . . . . . . . . . . . 8 3.1. Route Table Entry . . . . . . . . . . . . . . . . . . . . 8 3.2. DYMO Messages . . . . . . . . . . . . . . . . . . . . . . 10 3.2.1. Generalized MANET Packet and Message Structure . . . . 10 3.2.2. Routing Message (RM) . . . . . . . . . . . . . . . . . 10 3.2.3. Route Error (RERR) . . . . . . . . . . . . . . . . . . 12 4. Detailed Operation . . . . . . . . . . . . . . . . . . . . . . 14 4.1. Sequence Numbers . . . . . . . . . . . . . . . . . . . . . 14 4.1.1. Maintaining a Sequence Number . . . . . . . . . . . . 14 4.1.2. Incrementing a Sequence Number . . . . . . . . . . . . 14 4.1.3. Sequence Number Rollover . . . . . . . . . . . . . . . 14 4.1.4. Actions After Sequence Number Loss . . . . . . . . . . 14 4.2. DYMO Routing Table Operations . . . . . . . . . . . . . . 14 4.2.1. Creating or Updating a Route Table Entry from Routing Message Information . . . . . . . . . . . . . 14 4.2.2. Route Table Entry Timeouts . . . . . . . . . . . . . . 16 4.3. Routing Message . . . . . . . . . . . . . . . . . . . . . 16 4.3.1. Routing Message Creation . . . . . . . . . . . . . . . 16 4.3.2. Routing Message Processing . . . . . . . . . . . . . . 16 4.3.3. Appending Additional Routing Information to an Existing Routing Message . . . . . . . . . . . . . . . 17 4.4. Route Discovery . . . . . . . . . . . . . . . . . . . . . 18 4.5. Route Maintenance . . . . . . . . . . . . . . . . . . . . 18 4.5.1. Active Link Monitoring . . . . . . . . . . . . . . . . 18 4.5.2. Updating Route Lifetimes . . . . . . . . . . . . . . . 19 4.5.3. Route Error Generation . . . . . . . . . . . . . . . . 19 4.5.4. Route Error Processing . . . . . . . . . . . . . . . . 20 4.6. General DYMO Packet and Message Processing . . . . . . . . 21 4.6.1. Packet Processing . . . . . . . . . . . . . . . . . . 21 4.6.2. Generic Message Pre-processing . . . . . . . . . . . . 21 4.6.3. Processing Unknown Message and TLV Types . . . . . . . 21 4.6.4. Generic Message Post-processing . . . . . . . . . . . 21 4.6.5. DYMO Control Packet Transmission . . . . . . . . . . . 21 4.7. Routing Prefix . . . . . . . . . . . . . . . . . . . . . . 21 4.8. Simple Internet Attachment and Gatewaying . . . . . . . . 22 4.9. Multiple Interfaces . . . . . . . . . . . . . . . . . . . 22 4.10. Packet Generation Limits . . . . . . . . . . . . . . . . . 23 5. Configuration Parameters . . . . . . . . . . . . . . . . . . . 24 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 25 Chakeres & Perkins Expires September 6, 2006 [Page 2] Internet-Draft DYMO March 2006 7. Security Considerations . . . . . . . . . . . . . . . . . . . 26 8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 27 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 28 9.1. Normative References . . . . . . . . . . . . . . . . . . . 28 9.2. Informative References . . . . . . . . . . . . . . . . . . 28 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 29 Intellectual Property and Copyright Statements . . . . . . . . . . 30 Chakeres & Perkins Expires September 6, 2006 [Page 3] Internet-Draft DYMO March 2006 1. Overview The Dynamic MANET On-demand (DYMO) routing protocol enables reactive, multihop routing between participating nodes that wish to communicate. The basic operations of the DYMO protocol are route discovery and route management. During route discovery the originating node initiates dissemination of a Route Request (RREQ) throughout the network to find the target node. During this dissemination process, each intermediate node records a route to the originating node. When the target node receives the RREQ, it responds with a Route Reply (RREP) unicast toward the originating node. Each node that receives the RREP records a route to the target node, and then the RREP is unicast toward the originating node. When the originating node receives the RREP, routes have then been established between the originating node and the target node in both directions. In order to react to changes in the network topology nodes maintain their routes and monitor their links. When a data packet is received for a route or link that is no longer available the source of the packet is notified. A Route Error (RERR) is sent to the packet source to indicate the current route is broken. Once the source receives the RERR, it can perform route discovery if it still has packets to deliver. In order to enable extension of the base specification, DYMO uses the generalized MANET packet and message format [5]. Additionally, by following the defined default behavior for nodes not understanding a particular type of information, future enhancements are handled in an understood and predetermined fashion. DYMO uses sequence numbers as they have been proven to ensure loop freedom [3]. Sequence numbers enable nodes to determine the order of DYMO route discovery messages, thereby avoiding use of stale routing information. All DYMO messages conform to the generalized MANET message and packet format [5] and are transmitted via UDP on port TBD. Chakeres & Perkins Expires September 6, 2006 [Page 4] Internet-Draft DYMO March 2006 2. Terminology DYMO Sequence Number (SeqNum) A DYMO Sequence Number is 16-bit number maintained by each node, and it is used to ensure loop-free routes. Hop Count (HopCnt) The number of hops a particular message or piece of information has traversed. IP Destination Address (IPDestinationAddress) The destination of a packet, determined by examining the IP header. IP Source Address (IPSourceAddress) The source of a packet, determined by examining the IP header. MANETcast Packet transmission to all neighboring MANET routers. MANETcast packets should be sent with an IPDestinationAddress of IPv4 TBD (IPv6 TBD), the MANETcastAddress. Originator (Orig) The Originator is the node that created a Routing Message in an effort to disseminate and possibly learn new routing information. Chakeres & Perkins Expires September 6, 2006 [Page 5] Internet-Draft DYMO March 2006 Prefix A Prefix indicates that an address is a network address, rather than a host address. If a Prefix is omitted, the address is assumed to be a host address. Routing Message (RM) A DYMO message that is used to distribute routing information. Route Invalidation Disabling the use of a route; causing it to be unavailable for forwarding data. Route Reply (RREP) Upon receiving a RREQ during route discovery, the target node generates a Route Reply (RREP). A RREP is used to disseeminate routing information on how to reach the Target. A RREP is a RM with a unicast IPDestinationAddress, indicating that this RM is to be unicast hop-by-hop toward the Target. Route Error (RERR) A node generates a Route Error (RERR) to disseminate that it does not have correct routing information about a particular destination, or set of destinations. A RERR is most often generated in response to a request to forward a data packet for which the current node does not have a valid route. Route Request (RREQ) A node generates a Route Request (RREQ) to discover a valid route to a particular destination (Target). A RREQ is used to disseminate routing information on how to reach the Originator of the RREQ. A RREQ is simply a RM with the MANETcastAddress in the IPDestinationAddress field of the IP packet, causing Chakeres & Perkins Expires September 6, 2006 [Page 6] Internet-Draft DYMO March 2006 distribution to all neighboring DYMO routers. Target The Target is the ultimate destination of a message. For RREQ this will be the desired destination. For RREP this will be the Originator of the RREQ. Valid Route A known route where the Route.ValidTimeout is greater than the current time. Chakeres & Perkins Expires September 6, 2006 [Page 7] Internet-Draft DYMO March 2006 3. Data Structures 3.1. Route Table Entry 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. o Route.DestAddress o Route.DeleteTimeout o Route.HopCnt o Route.IsGateway o Route.NextHopAddress o Route.NextHopInterface o Route.Prefix o Route.SeqNum o Route.ValidTimeout These fields are defined as follows: Route Node Address (Route.DestAddress) The IP address of the node associated with the routing table entry. Route Delete Timeout (Route.DeleteTimeout) If the time current is after Route.DeleteTimeout the corresponding routing table entry MUST be deleted. Route Hop Count (Route.HopCnt) The number of intermediate node hops before reaching the Route.DestAddress. Chakeres & Perkins Expires September 6, 2006 [Page 8] Internet-Draft DYMO March 2006 Route Is Gateway (Route.IsGateway) 1-bit selector indicating whether the Route.DestAddress is a gateway, see Section 4.8. Route Next Hop Address (Route.NextHopAddress) The IP address of the next node on the path toward the Route.DestAddress. Route Next Hop Interface (Route.NextHopInterface) The interface used to send packets toward the Route.DestAddress. Route Prefix (Route.Prefix) 8-bit field that specifies the size of the subnet reachable through the Route.DestAddress, see Section 4.7. The definition of the Prefix field is different for gateways; entries with Route.IsGateway set to one (1), see Section 4.8. Route Sequence Number (Route.SeqNum) The sequence number of the Route.DestAddress, zero (0) if unknown. Route.ValidTimeout The time at which a route table entry is scheduled to be invalidated. The routing table entry is no longer considered valid if the current time is after Route.ValidTimeout. Chakeres & Perkins Expires September 6, 2006 [Page 9] Internet-Draft DYMO March 2006 3.2. DYMO Messages 3.2.1. Generalized MANET Packet and Message Structure All DYMO messages conform to the generalized packet and message format as described in [5]. 3.2.2. Routing Message (RM) Routing messages are used to disseminate routing information. The two message types are RREQ and RREP and they have the same general format. RREQ messages require a response, while RREP are responses to RREQ. Routing message creation and processing are described in Section 4.3. Example Simple RREQ/RREP Routing Message 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | msg-type | RSRV |U|N|0|1| msg-size | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | msg-ttl | msg-hopcnt | msg-tlv-block-size=0 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Head Length | Head |Number Tails=2 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | TailOrig | TailTarget | tlv-block-size | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |DYMOSEQNUM-type| TLV Length | Orig.SeqNum.: +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ :.Orig.SeqNum | Target.SeqNum | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 1 o RM conform to the generalized message format. o msg-type = DYMO-RREQ or DYMO-RREP o msg-semantics * RM indicate inclusion of msg-ttl and msg-hop-count in msg- header-info, by setting bit 1 o msg-header-info Chakeres & Perkins Expires September 6, 2006 [Page 10] Internet-Draft DYMO March 2006 * RM contains msg-ttl * RM contains msg-hop-count o add-block entries * RM contain 1 and only 1 address marked as Originator - If no address is marked as the originator the first address is assumed to be the Originator * if the RM is unicast (the IPDestinationAddress is a unicast address), RM contain 1 and only 1 address marked as Target (Target) - if no address is marked the second address is assumed to be the Target o add-tlv * RM contain the DYMO Sequence Number of the Originator (Orig.SeqNum) in a DYMO Sequence Number tlv * RM should contain the SeqNum for each address. If the SeqNum is not included a value of Zero (0) is assumed. For the Target the SeqNum will be the Last Known SeqNum (Target.SeqNum) or Zero (0) to indicate that only the Target can reply * RM should contain the HopCnt for each address. If HopCnt is not included, it is assumed to be zero (unknown). For the Target the HopCnt should be the Last Known HopCnt (Target.HopCnt) * RM should contain a Prefix for each address that is not a host address. If a prefix is not included in conjunction with an address, it is assumed zero (host address only). For more information on advertising a Prefix see Section 4.7. * RM should contain a Gateway tlv for an address that is a gateway. If gateway indicator is not included in association with an address, the address is assumed to not be a gateway. For more information on gateway operation see Section 4.8. Chakeres & Perkins Expires September 6, 2006 [Page 11] Internet-Draft DYMO March 2006 3.2.3. Route Error (RERR) Example Simple RERR Message 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | rerr-msg-type | RSRV |U|N|0|1| msg-size | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | msg-ttl | msg-hopcnt | msg-tlv-block-size=0 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Head Length | Head |Number Tails=1 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Tail1 | tlv-block-size |dymo-seqnum-typ| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | TLV Length | Tail1.SeqNum | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 2 o RERR conform to the generalized message format. o msg-type = DYMO-RERR o msg-semantics * RERR indicates inclusion of msg-ttl and msg-hop-count in msg- header-info, using bit 1 o msg-header-info * RERR contain msg-ttl * RERR contain msg-hop-count o add-block entries * All addresses are considered unreachable unless marked otherwise o add-tlvs * RERR should contain SeqNum for each unreachable node. If the SeqNum is not included in the message it is assumed to be zero (unknown) * RERR should contain the Last Known HopCnt for each unreachable node. If the HopCnt is not included in the message it is Chakeres & Perkins Expires September 6, 2006 [Page 12] Internet-Draft DYMO March 2006 assumed to be zero (unknown) Chakeres & Perkins Expires September 6, 2006 [Page 13] Internet-Draft DYMO March 2006 4. Detailed Operation 4.1. Sequence Numbers 4.1.1. Maintaining a Sequence Number DYMO requires each node in the network to maintain its own DYMO sequence number (OwnSeqNum), a 16-bit unsigned integer. The circumstances for a node to change its OwnSeqNum are described in Section 4.3.1. 4.1.2. Incrementing a Sequence Number When a node increments its OwnSeqNum (as described in Section 4.3.1 and Section 4.3.2) it MUST do so by treating the sequence number value as if it was an unsigned number. The sequence number zero (0) is reserved and is used in several DYMO data structures to represent an unknown sequence number. 4.1.3. Sequence Number Rollover If the sequence number has been assigned to be the largest possible number representable as a 16-bit unsigned integer (i.e., 65535), then the sequence number MUST be set to 256 when incremented. Setting the sequence number to 256 allows other nodes to detect that the number has rolled over and the node has not lost its sequence number. 4.1.4. Actions After Sequence Number Loss A node SHOULD maintain its sequence number in persistent storage. If a node's OwnSeqNum is lost, it must take certain actions to avoid creating routing loops. To prevent this possibility after sequence number loss a node MUST wait for at least ROUTE_DELETE_PERIOD before fully participating in the DYMO routing protocol. If a DYMO control message is received during this waiting period, the node SHOULD process it normally but MUST not transmit or retransmit any RM. If a data packet is received for forwarding to another destination during this waiting period the node MUST generate a RERR message indicating that this route is not available and reset its waiting period. RERR generation is described in Section 4.5.3. At the end of the waiting period a node sets its sequence number to one (1). 4.2. DYMO Routing Table Operations 4.2.1. Creating or Updating a Route Table Entry from Routing Message Information Chakeres & Perkins Expires September 6, 2006 [Page 14] Internet-Draft DYMO March 2006 While processing a RM, as described in Section 4.3.2, a node checks its routing table for an entry to the Node.Address using longest- prefix matching [6]. In the event that no matching entry is found, an entry is created. If a matching entry is found, the routing information about Node.Address contained in this RM is NOT stale if the result of subtracting the Route.SeqNum from Node.SeqNum is equal to zero (0) using signed 16-bit arithmetic but it SHOULD be disregarded if: o the Route.ValidTimeout has not passed and Node.HopCnt is greater than or equal to Route.HopCnt, OR o the Route.ValidTimeout has passed and Node.HopCnt is greater than Route.HopCnt plus one (1). If the information associated with this Node.Address is stale or disregarded and this Node.Address is the Originator then this DYMO message MUST be dropped. For other Node.Addresses that are stale or disregarded, the information is simply removed from the RM. Removing stale and disregarded routing informations ensures that unused information is not propagated further. If the route information for Node.Address is not stale or disregarded, then the following actions occur to the route table entry for Node.Address: 1. the Route.HopCnt is set to the Node.HopCnt, 2. the Route.IsGateway is set to the G-bit, 3. the Route.NextHopAddress is set to the node that transmitted this DYMO packet (IPSourceAddress), 4. the Route.NextHopInterface is set to the interface that this DYMO packet was received on, 5. the Route.Prefix is set to Node.Prefix,, 6. the Route.SeqNum is set to the Node.SeqNum, 7. and the Route.ValidTimeout is set to the current time + ROUTE_TIMEOUT. If a valid route exists to Node.Address at this point, the route can be used to send any queued data packets and to fulfill any outstanding route requests. Chakeres & Perkins Expires September 6, 2006 [Page 15] Internet-Draft DYMO March 2006 4.2.2. Route Table Entry Timeouts If the current time is after Route.DeleteTimeout the corresponding routing table entry MUST be deleted. If the current time is later than a routing entry's Route.ValidTimeout, the route is stale and it is not be used to route packets. The information in invalid entries can still be used for filling fields in outgoing RM with last known values. 4.3. Routing Message 4.3.1. Routing Message Creation When a node creates a RREQ it SHOULD increment its OwnSeqNum by one according to the rules specified in Section 4.1.2. When a node creates a RREP in response to a RREQ, it MUST increment its OwnSeqNum under the following conditions: o Target.SeqNum is greater than OwnSeqNum OR o Target.SeqNum is equal to OwnSeqNum AND Target.HopCnt is unknown OR o Target.SeqNum is equal to OwnSeqNum AND Orig.HopCnt is unknown OR o Target.SeqNum is equal to OwnSeqNum AND Target.HopCnt (the last know hop count value) is less than to Orig.HopCnt (the number of hops traversed by this RREQ to reach the target). In either case (both RREQ and RREP), the node MUST add the Orig.Address to the add-block and the Orig.SeqNum to the add-tlv- block. It sets the Orig.Address to its own address. The Orig.SeqNum is the node's OwnSeqNum. The node MAY advertise a prefix using the Prefix add-tlv, as described in Section 4.7. Otherwise, the Prefix add-tlv is not included. The node MAY advertise it is a gateway by using a gateway add-tlv, as described in Section 4.8. Otherwise, the gateway add-tlv is not included. The msg-ttl SHOULD be set to NET_DIAMETER, but MAY be set smaller. The msg-hopcnt is set to zero (0). the case of RREQ, the msg-ttl MAY be set in accordance with an expanding ring search as described in [2] to limit the RREQ propagation to a subset of the network and possibly reduce route discovery overhead. 4.3.2. Routing Message Processing After general message pre-processing (Section 4.6.2), a route to the Originator is then created or updated, as described in Section 4.2.1. Chakeres & Perkins Expires September 6, 2006 [Page 16] Internet-Draft DYMO March 2006 If a valid route to the Originator is not created or updated then the message MUST be dropped. Each additional address in the address block(s) SHOULD be processed except the Target. For each of these addresses the Node.HopCnt associated with the address is incremented by one (1) if it exists and is not zero, then a route is created or updated as defined in Section 4.2.1. The updating of the HopCnt occurs after processing. Each address resulting in a valid route entry may alleviate a future route discovery. Any addresses that do not yield a valid route or that are not processed MUST be removed from the RM. Only valid routing information is propagated within RM messages. If this node is the Target AND this is a RREQ, this node responds with a RREP. The Target creates a new RREP as described in Section 4.3.1. The Target.Address in the new RM is set to the Orig.Address from the RM currently being processed. The Target.HopCnt is the hop count for the Orig.Address. The IPDestinationAddress is set to the Route.NextHopAddress for the Orig.Address of the current RM being processed. The Target.SeqNum is set to Route.SeqNum for Orig.Address from the current RM being processed. Then the new RM undergoes post-processing, according to Section 4.6.4. After processing a RM, a node MAY append its routing information to the RM, according to the process described in Section 4.3.3. The additional routing information will reduce route discoveries to this node. If all nodes along the path append their information path information will also be available. If this node is not the Target.Address and this is a RREQ the current RM SHOULD be MANETcast. If this node is not the Target Address and this is a RREP the current RM SHOULD be unicast to the next hop address on the route to the Target. If this node is the Target.Address, the current message is processed, but this message is not forwarded or retransmitted. 4.3.3. Appending Additional Routing Information to an Existing Routing Message Appending routing information will alleviate route discovery attempts to this node from other nodes that process the resultant RM information. Nodes MAY append a their routing information to a RM processed if they believe that this additional routing information will alleviate future RREQ. Prior to appending their address to a RM, a node MUST increment its Chakeres & Perkins Expires September 6, 2006 [Page 17] Internet-Draft DYMO March 2006 OwnSeqNum as defined in Section 4.1.2. Then it appends its IP address and OwnSeqNum. It MAY also append its Prefix and G-bit to the RM. This Node.HopCnt is set to one (1) if included. Several length fields MUST also be adjusted to include the newly inserted information. 4.4. Route Discovery A node generates a Route Request (RREQ) to discover a route to a particular destination (Target). If a sequence number is known for the Target it is placed in the RREQ. Otherwise, Target.SeqNum assumed to be unknown by processing nodes. A Target.SeqNum of zero (0) MAY be set to indicate that only the destination may respond to this RREQ. If a previous value of the HopCnt is known for the Target it is placed in a corresponding add-tlv HopCnt. Otherwise, the HopCnt is not included. The IPDestinationAddress is set to the MANETcastAddress. Then the RM is transmitted according to the procedure defined in Section 4.6.5. After issuing a RREQ, the originating node waits for a route to be created to the Target. If a route is not found within RREQ_WAIT_TIME milliseconds, this node MAY again try to discover a route by issuing another RREQ. To reduce congestion in a network, repeated attempts at route discovery for a particular Target SHOULD utilize a binary exponential backoff. The first time a node issues a RREQ, it waits RREQ_WAIT_TIME milliseconds for a route to the Target. If a route is not found within that time, the node MAY send another RREQ. If a route is not found within two (2) times the current waiting time, another RREQ may be sent, up to a total of RREQ_TRIES. 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. If a route discovery has been attempted RREQ_TRIES times without receiving a route to the Target, all data packets destined for the corresponding Target SHOULD be dropped from the buffer and a Destination Unreachable ICMP message SHOULD be delivered to the application. 4.5. Route Maintenance 4.5.1. Active Link Monitoring Before a route can be used for forwarding a packet, it MUST be Chakeres & Perkins Expires September 6, 2006 [Page 18] Internet-Draft DYMO March 2006 checked to make sure that the route is still valid. If the Route.ValidTimeout is earlier than the current time, the packet cannot be forwarded, and a RERR message MUST be generated (see section Section 4.5.3). In this case, the Route.DeleteTimeout is set to Route.ValidTimeout + ROUTE_DELETE_TIMEOUT. If the current time is after Route.DeleteTimeout, then the route MUST be deleted, though a route MAY be deleted at any time. Nodes MUST monitor links on active routes. This may be accomplished by one or several mechanisms. Including: o Link layer feedback o Hello messages o Neighbor discovery o Route timeout o Other monitoring mechanisms or heuristics Upon detecting a link break the detecting node MUST set the Route.ValidTimeout to the current time for all active routes utilizing the broken link. A RERR MUST be issued if a data packet is received and it cannot be delivered to the next hop. RERR generation is described in Section 4.5.3. A RERR MAY be issued after detecting a broken link of an active route to quickly notify nodes that a link break occurred and a route or routes are no longer available. If a route has not been used, a RERR SHOULD NOT be generated unless generation is expected to reduce future control traffic. 4.5.2. Updating Route Lifetimes To avoid route timeouts for active routes, a node MUST update the Route.ValidTimeout to the IPSourceAddress to be the current time + ROUTE_TIMEOUT upon receiving a data packet. To avoid route timeouts for active routes, a node SHOULD update the Route.ValidTimeout to the IPDestinationAddress to be the current time + ROUTE_TIMEOUT upon successfully transmitting a packet to the next hop. 4.5.3. Route Error Generation When a data packet is received for a destination without a valid Chakeres & Perkins Expires September 6, 2006 [Page 19] Internet-Draft DYMO March 2006 routing table entry, a Route Error (RERR) MUST be generated by this node. A RERR informs the source that the route does not exist, is no longer available, or is now invalid. In a new RERR, the address of unreachable node (IPDestinationAddress) from the data packet is inserted. If a value for the unreachable node's SeqNum is known, it is placed in the RERR; otherwise, if unknown it will be assumed to be zero (0). The msg-ttl SHOULD be set to NET_DIAMETER, but may be set smaller to limit the scope of the RERR. The msg-hopcnt is set to zero (0). The IPDestinationAddress is set to the MANETcastAddress. This option will notify the maximum number of nodes of the broken link. Additional unreachable nodes that required the same unavailable link (routes with the same Route.NextHopAddress and Route.NextHopInterface) MAY be added to the RERR. For each unreachable node the Address is appended. The SeqNum if know should also be included. Appending additional routing information notifies each processing node of additional routes that are no longer available. The RERR is then processed as described in Section 4.6.5. 4.5.4. Route Error Processing When a node processes a RERR, it SHOULD set the Route.ValidTimeout to the current time for each Address that meets all of the following conditions: 1. The Route.NextHopAddress is the same as the RERR IPSourceAddress. 2. The Route.NextHopInterface is the same as the interface on which the RERR was received. 3. The Node.SeqNum is zero (0), unknown, OR the result of subtracting Route.SeqNum from Node.SeqNum is less than or equal to zero using signed 16-bit arithmetic. Each Node.Address that did not result in a change to Route.ValidTimeout SHOULD be removed from the RERR, since propagation of this information should not result in any benefit. Prior to post processing a node MAY remove any unreachable node address and its associated information to decrease the message size. If this node is the Target and the IPDestinationAddress is its own Address then it may stop processing. Chakeres & Perkins Expires September 6, 2006 [Page 20] Internet-Draft DYMO March 2006 If at least one unreachable node address remains in the RERR it SHOULD be handled as described in Section 4.6.4 to continue notification of nodes effected by the broken link. Otherwise, the RERR is dropped. 4.6. General DYMO Packet and Message Processing 4.6.1. Packet Processing The length of IP addresses (32-bits for IPv4 and 128-bits for IPv6) inside DYMO messages are dependent on the IP packet header. For example, if the IP header uses IPv6 addresses then all messages and addresses contained in the payload use IPv6 addresses. 4.6.2. Generic Message Pre-processing Each message undergoes pre-processing before the message specific processing occurs. During pre-processing, the msg-ttl is decremented by one (1) and the msg-hopcnt is incremented by one (1). 4.6.3. Processing Unknown Message and TLV Types We expect the next version of the generalized MANET packet and message format [5] to include message semantic bits and tlv semantic bits to control the behavior of unknown types. 4.6.4. Generic Message Post-processing If the msg-ttl of any message is zero (0) after processing it MUST be dropped. 4.6.5. DYMO Control Packet Transmission Packet transmission and re-transmission are controlled by the IPDestinationAddress. If the IPDestinationAddress is a unicast address, the packet IPDestinationAddress is replaced by the Route.NextHopAddress from a route table lookup for the Target. If a route for the Target is unknown or invalid the packet is dropped and a RERR SHOULD be generated. For all currently defined DYMO packets the IPTTL (IPMaxCount) SHOULD be set to 1 (IPTTL=1), since all DYMO packet communications are exchanged between direct neighbors only. 4.7. Routing Prefix Any node MAY advertise connectivity to a subset of node addresses within its address space by using a Prefix tlv [5]. The nodes (other Chakeres & Perkins Expires September 6, 2006 [Page 21] Internet-Draft DYMO March 2006 than the advertising node) within the advertised Prefix SHOULD NOT participate in the MANET and MUST be reachable by forwarding packets to the node advertising connectivity. For example, 192.168.1.1 with a prefix of 16 indicates all nodes with the prefix 192.168.X.X are reachable through 192.168.1.1. The meaning of the Prefix field is altered for routes to the gateway; Route.IsGateway is one (1). If the G-bit is set the Prefix in association with the IP address indicates that all nodes outside the subnet are reachable via the gateway node. For example, a route to a gateway with IP address 192.168.1.1 and a prefix of 16 indicates that all nodes with an IP address NOT matching 192.168.X.X are reachable via this node. 4.8. Simple Internet Attachment and Gatewaying Simple Internet attachment consists of a network of MANET nodes connected to the Internet via a single gateway node. The gateway is responsible for responding to RREQs for Targets outside its configured MANET subnet, as well as delivering packets to destinations outside the MANET. MANET nodes wishing to be reachable from nodes in the Internet MUST have IP addresses within the gateway's configured and advertised MANET subnet. Given a node with a globally routeable address or care-of address handled by the gateway, the gateway is responsible for routing and forwarding packets received from the Internet destined for nodes inside its MANET subnet. Since many nodes may commonly wish to communicate with the gateway, the gateway SHOULD indicate to nodes that it is a gateway by using the gateway tlv in any RM created or processed. The gateway tlv indicates to nodes in the MANET that the Node.Address is attached to the Internet and is capable of routing data packets to all nodes outside of the configured MANET subnet, defined by the Node.Address and Node.Prefix fields. 4.9. Multiple Interfaces It is likely that DYMO will be used with multiple wireless 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 MANETcast packet SHOULD send the packet on all interfaces that have been configured for DYMO operation. Chakeres & Perkins Expires September 6, 2006 [Page 22] Internet-Draft DYMO March 2006 4.10. Packet Generation Limits To avoid congestion, a node SHOULD NOT transmit more than RATE_LIMIT control messages per second. RREQ packets SHOULD be discarded before RREP or RERR packets. Chakeres & Perkins Expires September 6, 2006 [Page 23] Internet-Draft DYMO March 2006 5. Configuration Parameters Here are some default parameter values for DYMO: Parameter Name Suggested Value --------------------------- --------------- NET_DIAMETER 10 RATE_LIMIT 10 ROUTE_TIMEOUT 5000 milliseconds ROUTE_DELETE_TIMEOUT 5*ROUTE_TIMEOUT RREQ_WAIT_TIME 1000 milliseconds RREQ_TRIES 3 For large networks or networks with frequent topology changes the default DYMO parameters should be adjusted using either experimentally determined values or dynamic adaptation. For example, in networks with infrequent topology changes ROUTE_TIMEOUT may be set to a much larger value. It is assumed that all nodes in the network share the same parameter settings. Different parameter values for ROUTE_TIMEOUT or ROUTE_DELETE_TIMEOUT in addition to arbitrary packet delays may result in frequent route breaks or routing loops. Chakeres & Perkins Expires September 6, 2006 [Page 24] Internet-Draft DYMO March 2006 6. IANA Considerations DYMO defines several message-types and tlv-types. A new registry will be created for the values for the various type fields, and the following values will be assigned: msg-type Value -------------------------------- ------- Route Request (DYMO-RREQ) 8 - TBD Route Reply (DYMO-RREP) 9 - TBD Route Error (DYMO-RERR) 10 - TBD address-tlv Value -------------------------------- ----- DYMO SeqNum (multivalue) 20 - TBD HopCnt (multivalue) 21 - TBD Prefix (multivalue) 0 [5] Gateway (zero length) 22 - TBD Originator 23 - TBD Target 24 - TBD Future values of the Type will be allocated using standard actions as described in [1]. For future Types that are unicast hop-by-hop (packets not sent to the MANETcastAddress), these Types MUST include the Target.Address field. Chakeres & Perkins Expires September 6, 2006 [Page 25] Internet-Draft DYMO March 2006 7. Security Considerations Currently, DYMO does not specify any special security measures. Routing protocols, however, are prime targets for impersonation attacks. In networks where the node membership is not known, it is difficult to determine the occurrence of impersonation attacks, and security prevention techniques are difficult at best. However, when the network membership is known and there is a danger of such attacks, DYMO messages must be protected by the use of authentication techniques, such as those involving generation of unforgeable and cryptographically strong message digests or digital signatures. While DYMO does not place restrictions on the authentication mechanism used for this purpose, IPsec Authentication Message (AH) is an appropriate choice for cases where the nodes share an appropriate security association that enables the use of AH. In particular, RM messages SHOULD be authenticated to avoid creation of spurious routes to a destination. Otherwise, an attacker could masquerade as that destination and maliciously deny service to the destination and/or maliciously inspect and consume traffic intended for delivery to the destination. RERR messages, while slightly less dangerous, SHOULD be authenticated in order to prevent malicious nodes from disrupting active routes between communicating nodes. If the mobile nodes in the ad hoc network have pre-established security associations, the purposes for which the security associations are created should include that of authorizing the processing of DYMO control packets. Given this understanding, the mobile nodes should be able to use the same authentication mechanisms based on their IP addresses as they would have used otherwise. Chakeres & Perkins Expires September 6, 2006 [Page 26] Internet-Draft DYMO March 2006 8. Acknowledgments DYMO is a descendant of the design of previous MANET reactive protocols, especially AODV [2] and DSR [4]. Changes to previous MANET reactive protocols stem from research and implementation experiences. Thanks to Elizabeth Belding-Royer for her long time authorship of DYMO. Additional thanks to Luke Klein-Berndt, Pedro Ruiz, Fransisco Ros and Koojana Kuladinithi for reviewing of DYMO, as well as several specification suggestions. Chakeres & Perkins Expires September 6, 2006 [Page 27] Internet-Draft DYMO March 2006 9. References 9.1. Normative References [1] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA Considerations Section in RFCs", RFC 2434, BCP 26, October 1998. [2] Perkins, C., Belding-Royer, E., and S. Das, "Ad hoc On-demand Distance Vector (AODV) Routing", RFC 3561, July 2003. [6] Baker, R., "Requirements for IP Version 4 Routers", RFC 1812, June 1995. 9.2. Informative References [3] 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. [4] Johnson, D. and D. Maltz, "Dynamic Source Routing (DSR) in Ad hoc Networks", In Mobile Computing, Chapter 5, pp. 153-181, 1996. [5] Clausen, T., Dearlove, C., and J. Dean, "Generalized MANET Packet/Message Format", February 2006. Chakeres & Perkins Expires September 6, 2006 [Page 28] Internet-Draft DYMO March 2006 Authors' Addresses Ian Chakeres Boeing Phantom Works The Boeing Company P.O. Box 3707 Mailcode 7L-49 Seattle, WA 98124-2207 USA Email: ian.chakeres@gmail.com Charlie Perkins Nokia Research Center 313 Fairchild Drive Mountain View, CA 94043 USA Phone: +1-650-625-2986 Fax: +1-650-625-2502 Email: charlie.perkins@nokia.com Chakeres & Perkins Expires September 6, 2006 [Page 29] Internet-Draft DYMO March 2006 Intellectual Property Statement The IETF takes no position regarding the validity or scope of any Intellectual Property Rights or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; nor does it represent that it has made any independent effort to identify any such rights. Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79. 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