Multicast and IGMP Snooping

Answered Question
Apr 1st, 2009

Hi,

I haven't had chance to learn about multicast properly yet however have a quick question. I understand that by default IGMP snooping is on (as shown from one of my 4500 switches below)

Global IGMP Snooping configuration:

-----------------------------------

IGMP snooping : Enabled

IGMPv3 snooping : Enabled

Report suppression : Enabled

TCN solicit query : Disabled

TCN flood query count : 2

however if I run a packetsniffer I can see HSRP etc messages, meaning they are being flooded to my port. Are the link local multicast addresses for things such as HSRP and VRRP treated differently, or is it being flooded because there is no further multicast config?

Thanks

I have this problem too.
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Correct Answer by Jon Marshall about 7 years 8 months ago

Mike

"Are the link local multicast addresses for things such as HSRP and VRRP treated differently" -

yes for reserved multicast addresses out of the 224.0.0.x range IGMP snooping has no effect, they will be flooded to all ports within that vlan.

Jon

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Correct Answer
Jon Marshall Wed, 04/01/2009 - 09:30

Mike

"Are the link local multicast addresses for things such as HSRP and VRRP treated differently" -

yes for reserved multicast addresses out of the 224.0.0.x range IGMP snooping has no effect, they will be flooded to all ports within that vlan.

Jon

mike_guy29 Thu, 04/02/2009 - 01:09

Hi,

Thank you for confirming that. I had suspected that.

Many thanks

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