[Linux-cluster] A better understanding of multicast issues

Digimer linux at alteeve.com
Sat Feb 12 16:23:48 UTC 2011

On 02/12/2011 10:36 AM, Corey Kovacs wrote:
> When a multicast group is "joined" the switch/router will periodically
> (three mins i think) send out a query to the members to see if the
> connection is still needed. If a member does not reply to this query,
> then the connection is dropped for that port. If a switch is rebooted,
> then it's up to the member to re-establish the connection I believe,
> not the switch. Snooping is not generally a problem unless it's broken
> in the switch/router firmware. If it is, then you might need an
> upgrade. We use Multicast for all sorts of things and have indeed run
> into some problems on devices like Flex-10 cards for HP c7000 blade
> chassis that didn't do igmp snooping correctly, but we have gotten
> fixes for these issues from various vendors.
> If you have a planned outage for a switch, you can have your network
> people relocate the querier for a particular multicast group to
> another switch accessible to say a bonded pair or something. Things
> get really odd if you are on two separate switches that aren't
> stacked.
> Generally speaking, multicast isn't hard, you just have to think backwards.
> -C

Thanks for the reply, Corey.

  When I replied to Kit, I think I addressed issues you both brought up
(yay head colds!). So let me extend my thanks to you here, this has
given my more to consider. I'll have to fire up tcpdump on the the
cluster and wait and see.

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