【正文】 ignored on reception. Hop Count The number of hops from the originating node to the node handling the request. This field also indicates the number of accumulated path node IP addresses and sequence numbers in the RREQ. RREQ ID A sequence number uniquely identifying the particular RREQ when taken in conjunction with the originating node39。 MUST be at least 1. Unreachable Destination IP Address The IP address of the destination that has bee unreachable due to a broken link. Unreachable Destination Sequence Number The sequence number in the route table entry for the destination listed in the previous Unreachable Destination IP Address field.. Route Reply Acknowledgment (RREPACK) Message Format 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +++++++++++++++++ | Type | Reserved | +++++++++++++++++ Type 4 Reserved Sent as 0。Mobile Ad Hoc Networking Working Group Charles E. PerkinsINTERNET DRAFT Nokia Research Center19 October 2003 Elizabeth M. BeldingRoyer University of California, Santa Barbara Ian D. Chakeres University of California, Santa Barbara Ad hoc OnDemand Distance Vector (AODV) Routing 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 mailing list. Distribution of this memo is unlimited. This document is an InternetDraft and is in full conformance with all provisions of Section 10 of RFC2026. InternetDrafts 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 InternetDrafts. InternetDrafts 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 InternetDrafts as reference material or to cite them other than as work in progress. The list of current InternetDrafts can be accessed at: The list of InternetDraft Shadow Directories can be accessed at: Abstract The Ad hoc OnDemand Distance Vector (AODV) routing protocol is intended for use by mobile nodes in an ad hoc network. It offers quick adaptation to dynamic link conditions, low processing and memory overhead, low network utilization, and unicast route determination to destinations within the ad hoc network. It uses destination sequence numbers to ensure loop freedom at all times (even in the face of anomalous delivery of routing control messages), avoiding problems (such as ``counting to infinity39。 ignored on reception.Perkins, BeldingRoyer, Chakeres Expires 19 April 2003 [Page 8]Internet Draft AODV 19 October 20036. AODV Operation This section describes the scenarios during which nodes generate Route Request (RREQ) and Route Reply (RREP) for unicast munication to a destination node and how the message fields are handled. In order to process the messages correctly, certain state information has to be maintained in the routing table for destinations of interest. All AODV messages are sent to port 654 using UDP.. Maintaining Sequence Numbers Every routing table at every node MUST include the latest information available about the sequence number for the IP address of each destination for which a routing table entry is maintained. This sequence number is called the destination sequence number. It is updated whenever a node receives new (., not stale) information about the sequence number from RREQ, RREP, or RERR messages that may be received related to that destination. AODV requires each node in the network to own and maintain its destination sequence number in order to guarantee the loopfreedom of all routes towards that node. A node increments its own sequence number in two circumstances: Immediately before a node initiates a route discovery, it MUST increment its own sequence number. This prevents conflicts with previously established reverse routes towards the originator of a RREQ. Immediately before a node issues a RREP in response to a RREQ, it MUST update its own sequence number to the maximum of its current sequence number and the destination sequence number in the RREQ packet plus one (1). When a node increments a sequence number, it MUST do so by treating the sequence number value as if it were an unsigned number. Additionally the sequence number zero (0) is reserved and MUST never be used. To acplish sequence number rollover, if the sequence number has already been assigned to be the largest possible number representable as a 32bit unsigned integer (., 4294967295), then it MUST then have a value of one (1) when it is incremented. This is in contrast to the manner in which the result of paring two AODV sequence numbers is to be treated (see below). In order to ascertain that information about a destination is not stale, the node pares its current numerical value for the sequence number in its routing table with that obtained from the ining AODV