network protocols handbook.pdf

90Protocols GuideTCP/IP - Network Layer ProtocolsProtocol NamePIM-DM: Protocol IndependentMulticast – Dense ModeProtocol DescriptionProtocol Independent Multicast (PIM) has two modes: SparseMode and Dense Mode. We focus on the Dense Mode in thisdocument.PIM-DM is mainly designed for multicast LAN applications, whilethe PIM-SM is for wide area, inter-domain networks. PIM-DMimplements the same flood-and-prune mechanism that DistanceVector Multicast Routing Protocol (DVMRP) and other densemode routing protocols employ. The main difference betweenDVMRP and PIM-DM is that PIM-DM introduces the conceptof protocol independence. PIM-DM can use the routing tablepopulated by any underlying unicast routing protocol to performreverse path forwarding (RPF) checks.ISPs typically appreciate the ability to use any underlying unicastrouting protocol with PIM-DM because they need not introduceand manage a separate routing protocol just for RPFchecks. Unicast routing protocols extended as Multiprotocol Extensionsto BGP (MBGP) and Multitopology Routing for IS-IS(M-ISIS) were later employed to build special tables to performRPF checks, but PIM-DM does not require them.PIM-DM can use the unicast routing table populated by OSPF,IS-IS, BGP, and so on, or PIM-DM can be configured to use aspecial multicast RPF table populated by MBGP or M-ISIS whenperforming RPF checks.Protocol StructureThe protocol format of PIM-DM is the same as that of PIM-SM:www.ietf.org) yet.Referencehttp://www.javvin.com/protocol/rfcPIM-DM.pdfPIM-DM: Protocol Specification Drafthttp://www.javvin.com/protocol/rfcPIMDM-refresh.pdfPIM-DM Refresh DraftPIM versionTypeReserved(Address length)Checksum• PIM version – The current PIM version is 2.• Type -- Types for specific PIM messages.• Address length -- Address length in bytes. The lengthof the address field throughout, in the specific message.• Reserved - The value of this field is set to 0, ignoreon receipt• Checksum - The 16-bit field is the one’s complementsum of the entire PIM message.Related protocolsPIM-SM, ICMP, RIP, OSPF, DVMRP, IS-IS, BGP, IGRP, EIGRPSponsor SourcePIM-DM has been discussed but yet not finalized by IETF (http://