Dvmrp; Chapter 30 Dvmrp; Dvmrp Overview; How Dvmrp Works - ZyXEL Communications ZyXEL Dimension ES-4124 User Manual

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This chapter introduces DVMRP and tells you how to configure it.

30.1 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

30.2 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.
4 The final multicast ("M") after pruning and grafting is shown in the next figure.
ES-4124 User's Guide
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DVMRP

Figure 134 on page 251.
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