Igmp Overview - Extreme Networks ExtremeWare XOS Guide Manual

Overview
NOTE
You can run either PIM-DM or PIM-SM per virtual LAN (VLAN).
PIM Mode Interoperation
An Extreme Networks switch can function as a PIM multicast border router (PMBR). A PMBR
integrates PIM-SM and PIM-DM traffic.
When forwarding PIM-DM traffic into a PIM-SM network, the PMBR acts as a virtual first hop and
encapsulates the initial traffic to RP. The PMBR forwards PIM-DM multicast packets to the RP, which, in
turn, forwards the packets to those routers that have joined the multicast group.
The PMBR also forwards PIM-SM traffic to a PIM-DM network, based on the (*.*.RP) entry. The PMBR
sends a (*.*.RP) join message to the RP, and the PMBR forwards traffic from the RP into the PIM-DM
network.
No commands are required to enable PIM mode interoperation. PIM mode interoperation is
automatically enabled when a dense mode interface and a sparse mode interface are enabled on the
same switch.

IGMP Overview

IGMP is a protocol used by an IP host to register its IP multicast group membership with a router.
Periodically, the router queries the multicast group to see if the group is still in use. If the group is still
active, a single IP host responds to the query, and group registration is maintained.
IGMP is enabled by default on the switch. However, the switch can be configured to disable the
generation of periodic IGMP query packets. IGMP should be enabled when the switch is configured to
perform IP unicast or IP multicast routing.
IGMP Snooping
IGMP snooping is a Layer 2 function of the switch; it does not require multicast routing to be enabled.
In IGMP snooping, the Layer 2 switch keeps track of IGMP reports and only forwards multicast traffic
to that part of the local network that requires it. IGMP snooping optimizes the use of network
bandwidth and prevents multicast traffic from being flooded to parts of the local network that do not
need it.
IGMP snooping is enabled by default on the switch. If IGMP snooping is disabled, all IGMP and IP
multicast traffic floods within a given VLAN. IGMP snooping expects at least one device on every
VLAN to periodically generate IGMP query messages.
When a port sends an IGMP leave message, the switch removes the IGMP snooping entry after 1000
milliseconds (the leave time is configurable, ranging from 0 to 10000 ms). The switch sends a query to
determine which ports want to remain in the multicast group. If other members of the VLAN want to
remain in the multicast group, the router ignores the leave message, but the port that requests removal
is removed from the IGMP snooping table.
If the last port within a VLAN sends an IGMP leave message and the router does not receive any
responses to the query, then the router immediately removes the VLAN from the multicast group.
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ExtremeWare XOS 11.1 Concepts Guide