Users Guide

Table Of Contents
IPv4 and IPv6 Multicast 1595
contain two ports, one on each connecting switch. A VLAN carrying multicast
traffic should never traverse a multicast router, as ingress multicast traffic is
Layer-2-switched across the VLAN, defeating the purpose of the multicast
router.
Determining Which Multicast Protocols to Enable
IGMP is required on any multicast router that serves IPv4 hosts. IGMP is not
required on inter-router links. MLD is required on any router that serves IPv6
hosts. MLD is not required on inter-router links. PIM-DM, PIM-SM, and
DVMRP are multicast routing protocols that help determine the best route
for IP (PIM and DVMRP) and IPv6 (PIM) multicast traffic.
IGMP is automatically enabled whenever an IPv4 multicast routing protocol
is enabled that requires it, i.e., PIM-SM, PIM-DM, and DVMRP via the CLI.
Likewise, MLD is automatically enabled whenever an IPv6 multicast routing
protocol is enabled that requires it (PIM-SM and PIM-DM) via the CLI.
IGMP and MLD may not be separately enabled or disabled via the CLI. They
may be separately enabled/disabled via the web.
For more information about when to use PIM-DM, see "Using PIM-DM as
the Multicast Routing Protocol" on page 1608. For more information about
when to use PIM-SM, see "Using PIM-SM as the Multicast Routing Protocol"
on page 1598. For more information about when to configure DVMRP, see
"Using DVMRP as the Multicast Routing Protocol" on page 1609.
What Is the Multicast Routing Table?
Multicast capable/enabled routers forward multicast packets based on the
routes in the Multicast Routing Information Base (MRIB). These routes are
created in the MRIB during the process of building multicast distribution
trees by the Multicast Protocols running on the router. Different IP Multicast
routing protocols use different techniques to construct these multicast
distribution trees.