Extreme Networks ExtremeWare XOS 10.1, Manual

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Overview
ExtremeWare XOS 10.1 Concepts Guide 219
The PMBR also forwards PIM-SM traffic to a PIM-DM network, based on the (*.*.RP) entry. The PMBR
sends a 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 requests, and only forwards multicast traffic to
the part of the local network that requires it. IGMP snooping optimizes the usage 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. The static IGMP snooping entries do not require
periodic query, but do require a query in order to retrieve them after the
clear igmp snooping
command.
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.
Static IGMP
To receive multicast traffic, a host needs to explicitly join a multicast group by sending an IGMP report,
then the traffic is forwarded to that host. There are situations where you would like multicast traffic to
be forwarded to a port where a multicast enabled host is not available (for example, testing multicast
configurations). Static IGMP emulates a host or router attached to a switch port, so that multicast traffic
will be forwarded to that port. To emulate a host so as to forward a particular multicast group to a port,
emulate a router to forward all multicast groups to a port. Use the following command to emulate a
host on a port:
configure igmp snooping vlan <vlan name> ports <portlist> add static group <group
address>
To emulate a multicast router on a port, use the following command: