Managing IPv4 and IPv6 Multicast 1157
What Is IGMP?
The Internet Group Management Protocol (IGMP) is used by IPv4 systems
(hosts, L3 switches, and routers) to report their IP multicast group
memberships to any neighboring multicast routers. The PowerConnect 7000
Series switch performs the multicast router role of the IGMP protocol, which
means it collects the membership information needed by the active multicast
routing protocol.
The PowerConnect 7000 Series switch also supports IGMP Version 3. Version
3 adds support for source filtering, which is the ability for a system to report
interest in receiving packets only from specific source addresses, as required to
support Source-Specific Multicast [SSM], or from all but specific source
addresses, sent to a particular multicast address. Version 3 is designed to be
interoperable with Versions 1 and 2.
Understanding IGMP Proxy
IGMP proxy enables a multicast router to learn multicast group membership
information and forward multicast packets based upon the group
membership information. The IGMP Proxy is capable of functioning only in
certain topologies that do not require Multicast Routing Protocols (i.e.,
DVMRP, PIM-DM, and PIM-SM) and have a tree-like topology, as there is no
support for features like reverse path forwarding (RPF) to correct packet route
loops.
The proxy contains many downstream interfaces and a unique upstream
interface explicitly configured. It performs the host side of the IGMP protocol
on its upstream interface and the router side of the IGMP protocol on its
downstream interfaces.
The IGMP proxy offers a mechanism for multicast forwarding based only on
IGMP membership information. The router must decide about forwarding
packets on each of its interfaces based on the IGMP membership
information. The proxy creates the forwarding entries based on the
membership information and adds it to the multicast forwarding cache
(MFC) in order not to make the forwarding decision for subsequent multicast
packets with same combination of source and group.
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