network protocols handbook.pdf

80Protocols GuideTCP/IP - Network Layer ProtocolsProtocol NameDVMRP: Distance Vector MulticastRouting ProtocolProtocol DescriptionDistance Vector Multicast Routing Protocol (DVMRP) is an Internetrouting protocol that provides an efficient mechanism forconnectionless message multicast to a group of hosts acrossan internetwork. DVMRP is an “interior gateway protocol” (IGP);suitable for use within an autonomous system, but not betweendifferent autonomous systems. DVMRP is not currently developedfor use in routing non-multicast datagrams, so a routerthat routes both multicast and unicast datagrams must run twoseparate routing processes.DVMRP is developed based upon RIP. DVMRP combines manyof the features of RIP with the Truncated Reverse Path Broadcasting(TRPB) algorithm. In addition, to allow experiments totraverse networks that do not support multicasting, a mechanismcalled tunneling was developed. The key differences ofDVMRP from RIP are: RIP routes and forwards datagrams to aparticular destination. The purpose of DVMRP is to keep track ofthe return paths to the source of multicast datagrams.DVMRP packets are encapsulated in IP datagrams, with an IPprotocol number of 2 (IGMP).Protocol StructureDVMRP uses the IGMP to exchange routing datagrams. DVMRPdatagrams are composed of two portions: a small, fixed lengthIGMP header, and a stream of tagged data.Related protocolsIP, IGMP, RIPSponsor SourceDVMRP is defined by IETF (http://www.ietf.org) in RFC 1075.Referencehttp://www.javvin.com/protocol/rfc1075.pdfDistance Vector Multicast Routing Protocol4 8 16 24 32 bitVersion Type Sub-Type ChecksumDVMRP Data stream• Version – It is 1.• Type – DVMRP type is 3.• Sub-type - The subtype is one of:1 = Response; the message provides routes tosome destination(s).2 = Request; the message requests routes to somedestination(s).3 = Non-membership report; the message providesnon-membership report(s).4 = Non-membership cancellation; the messagecancels previous non-membership report(s).• Checksum -- One’s complement of the one’s complementsum of the DVMRP message. The checksummust be calculated upon transmission and must bevalidated on reception of a packet. The checksum ofthe DVMRP message should be calculated with thechecksum field set to zero.