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Running IGMP Querier on 6500

Hi,

In order to support multicast for Unified communication for cluster establishment of Linux based servers, we have been advised to run following commands.

ip igmp snooping querier 10.1.31.50  [subnet doesn't matter, write any ip you want]
   no ip igmp snooping link-local-groups-suppression    [this ensures that igmp reports containing two-groups can pass through switches successfully]
   name vlan-name

Having very less information on Multicast, i just want to understand the impact of these commands on a 6500 switch? Also,

i have attached a Cisco document which informs about 5 different solution for solving the same problem of Multicast. Can you please comment if there is any better alternative for this, and comparison along with the pro's and cons?

regards,

Mohsin

2 REPLIES
Hall of Fame Super Blue

Re: Running IGMP Querier on 6500

Mohsin

IGMP snooping runs in hardware on the 6500 so you should be fine. When you say it can be any IP address, it needs to be the IP of a L3 vlan intferace on the switch.

The key thing to note though is that will only work within the same vlan ie. it wouldn't work if you wanted to pass multicast traffic between vlans.

If the switch supports IGMP snooping querier and you only need multicast within the same vlan that is the way to go.

Jon

Hall of Fame Super Silver

Re: Running IGMP Querier on 6500

Hello Mohsin,

in addiition to Jon's post:

IGMP snooping attempts to optimize  the forwarding of multicast flows within a single Vlan/broadcast domain by listening to IGMP reports from all interested receivers. It builds a dynamic list of L2 ports interested in receiving a specific multicast MAC address

We could call it a L2 output interface list.

The problem arises when no L3 device send out IGMP queries this would cause IGMP snooping to miss IGMP reports that are not sent anymore (they are sent as answer to IGMP query except at the beginning when application on PC signals interest to the group).

The IGMP querier becomes a good solution when the multicast traffic should be confined in a single vlan: instead of enabling PIM you can enable on only ONE device the IGMP querier function that to work uses as source address the ip address the L3 SVI.

This provide a network device that performs periodic queries making IGMP snooping to work correctly.

There should be an interesting exclusion: link local addresses (224.0.0.x) shouldn't be processed by IGMP snooping because most of these are in use by the routing protocols including unicast routing protocols and PIM itself..

If the multicast stream has to be routed, that is it has to go over different IP subnets you need to enable ip multicast routing and you need full featured PIM enabled on the SVI L3 interface.

So you need to check if all cluster members are in the same IP subnet or not.

Hope to help

Giuseppe

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