IBM RackSwitch G8000, Application Manual

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© Copyright IBM Corp. 2011
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Chapter 19. Internet Group Management Protocol
Internet Group Management Protocol (IGMP) is used by IPv4 Multicast routers
(Mrouters) to learn about the existence of host group members on their directly
attached subnet. The IPv4 Mrouters get this information by broadcasting IGMP
Membership Queries and listening for IPv4 hosts reporting their host group
memberships. This process is used to set up a client/server relationship between an
IPv4 multicast source that provides the data streams and the clients that want to
receive the data. The switch supports three versions of IGMP:
•
IGMPv1: Defines the method for hosts to join a multicast group. However, this
version does not define the method for hosts to leave a multicast group. See
RFC 1112 for details.
• IGMPv2: Adds the ability for a host to signal its desire to leave a multicast group.
See RFC 2236 for details.
• IGMPv3: Adds support for source filtering by which a host can report interest in
receiving packets only from specific source addresses, or from all but specific
source addresses, sent to a particular multicast address. See RFC 3376 for
details.
The G8000 can perform IGMP Snooping, and connect to static Mrouters.
The following topics are discussed in this chapter:
•
“IGMP Terms” on page 215
• “How IGMP Works” on page 216
• “IGMP Capacity and Default Values” on page 217
• “IGMP Snooping” on page 218
• “IGMP Relay” on page 228
• “Additional IGMP Features” on page 236
IGMP Terms
The following are commonly used IGMP terms:
•
Multicast traffic: Flow of data from one source to multiple destinations.
• Group: A multicast stream to which a host can join. Multicast groups have IP
addresses in the range: 224.0.0.0 to 239.255.255.255.
• IGMP Querier: A router or switch in the subnet that generates Membership
Queries and processes membership reports and leave messages.
• IGMP Snooper: A Layer 3 device that forwards multicast traffic only to hosts that
are interested in receiving multicast data. This device can be a router or a Layer
3 switch.
• Multicast Router: A router configured to make routing decisions for multicast
traffic. The router identifies the type of packet received (unicast or multicast) and
forwards the packet to the intended destination.
• IGMP Proxy: A device that filters Join messages and Leave messages sent
upstream to the Mrouter to reduce the load on the Mrouter.
• Membership Report: A report sent by the host that indicates an interest in
receiving multicast traffic from a multicast group.
• Leave: A message sent by the host when it wants to leave a multicast group.
• FastLeave: A process by which the switch stops forwarding multicast traffic to a
port as soon as it receives a Leave message.