78 Switch Features
IGMP Snooping Querier
When Protocol Independent Multicast (PIM) and IGMP are enabled in a
network with IP multicast routing, the IP multicast router acts as the IGMP
querier. However, if the IP-multicast traffic in a VLAN needs to be Layer 2
switched only, an IP-multicast router is not required. The IGMP Snooping
Querier can perform the IGMP snooping functions on the VLAN.
MLD Snooping
In IPv4, Layer 2 switches can use IGMP Snooping to limit the flooding of
multicast traffic by dynamically configuring Layer 2 interfaces so that
multicast traffic is forwarded to only those interfaces associated with IP
multicast address.
In IPv6, MLD snooping performs a similar function. With MLD snooping,
IPv6 multicast data is selectively forwarded to a list of ports intended to
receive the data (instead of being flooded to all of the ports in a VLAN). This
list is constructed by snooping IPv6 multicast control packets.
Multicast VLAN Registration
The Multicast VLAN Registration (MVR) protocol, like IGMP Snooping,
allows a Layer 2 switch to listen to IGMP frames and forward the multicast
traffic only to the receivers that request it. Unlike IGMP Snooping, MVR
allows the switch to listen across different VLANs. MVR uses a dedicated
VLAN, which is called the multicast VLAN, to forward multicast traffic over
the Layer 2 network to the various VLANs that have multicast receivers as
members.
Layer 3 Multicast Features
For information about configuring L3 multicast features, see "Managing IPv4
and IPv6 Multicast" on page 1137.
Distance Vector Multicast Routing Protocol
Distance Vector Multicast Routing Protocol (DVMRP) exchanges probe
packets with all DVMRP-enabled routers, establishing two way neighboring
relationships and building a neighbor table. It exchanges report packets and
creates a unicast topology table, which is used to build the multicast routing
table. This multicast route table is then used to route the multicast packets.
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