Cisco Nexus 7000 Series Configuration Manual page 148

Configuring Global IGMP Snooping Parameters
The following are additional notes about some of the IGMP snooping parameters.
• IGMP Snooping Proxy parameter
To decrease the burden placed on the snooping switch during each IGMP general query (GQ) interval,
Cisco NX-OS provides a way to decouple the periodic general query behavior of the IGMP snooping
switch from the query interval configured on the multicast routers.
Beginning with Cisco NX-OS release 5.2(1), a configuration option became available to enable the Cisco
Nexus 7000 switch to consume IGMP general queries from the multicast router, rather than flooding the
general queries to all the switchports.
When receiving a general query, the switch produces proxy reports for all currently active groups and
distributes the proxy reports over the period specified by the MRT that is specified in the router query.
At the same time, independent of the periodic general query activity of the multicast router, the switch
sends an IGMP general query on each port in the VLAN in a round-robin fashion. It cycles through all
the interfaces in the VLAN at the rate given by the following formula.
Rate = {number of interfaces in VLAN} * {configured MRT} * {number of VLANS}
When running queries in this mode, the default MRT value is 5,000 milliseconds (5 seconds), which
means that in a switch that has 500 switchports in a VLAN, it would take 2,500 seconds (40 minutes) to
cycle through all the interfaces in the system. This is also true when the Cisco Nexus 7000 switch itself
is the querier.
This behavior ensures that only one host responds to a general query at a given time and it keeps the
simultaneous reporting rate below the packet-per-second IGMP capability of the switch (approximately
3,000 to 4,000 pps).
The ip igmp snooping proxy general-queries[mrt] command causes the snooping function to proxy
reply to general queries from the multicast router, while also sending round-robin general queries on
each switchport with the specified MRT value (the default MRT value is 5 seconds).
• IGMP Snooping Group-timeout parameter
Configuring the group-timeout parameter disables the behavior of expiring membership based on three
missed general queries. The group membership remains on a given switchport until the switch receives
an explicit IGMP leave on that port.
The ip igmp snooping group-timeout {timeout|never} command modifies or disables the behavior of
an expiring IGMP snooping group membership after three missed general queries.
Procedure
Step 1
Cisco Nexus 7000 Series NX-OS Multicast Routing Configuration Guide
134
Note
When using this option, you must change the ip igmp snooping group-timeout
parameter to a high value or to never time out.
Command or Action
config t
Example:
switch# config t
switch(config)#
Configuring IGMP Snooping
Purpose
Enters global configuration mode.