ZyXEL Communications XGS4600 Series, Руководство пользователя

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Chapter 52 DVMRP
XGS4600 Series User’s Guide
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HAPTER
52
DVMRP
This chapter introduces DVMRP and tells you how to configure it.
52.1 DVMRP Overview
DVMRP (Distance Vector Multicast Routing Protocol) is a protocol used for routing multicast data within
an autonomous system (AS). This DVMRP implementation is based on draft-ietf-idmr-dvmrp-v3-10.
DVMRP provides multicast forwarding capability to a layer-3 switch that runs both the IPv4 protocol (with
IP Multicast support) and the IGMP protocol. The DVMRP metric is a hop count of 32.
IGMP is a protocol used for joining or leaving a multicast group. You must have IGMP enabled when you
enable DVMRP; otherwise you see the screen as in
Figure 378 on page 476 .
52.2 How DVMRP Works
DVMRP uses the Reverse Path Multicasting (RPM) algorithm to generate an IP Multicast delivery tree.
Multicast packets are forwarded along these multicast tree branches. DVMRP dynamically learns host
membership information using Internet Group Management Protocol (IGMP). The trees are updated
dynamically to track the membership of individual groups.
1
Initially an advertisement multicast packet is broadcast (“ B ” in the following figure).
2
DVMRP-enabled Layer-3 devices that do not have any hosts in their networks that belong to this
multicast group send back a prune message (“
P ”).
3
If hosts later join the multicast group, a graft message (“ G ”) to undo the prune is sent to the parent.