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Re: [Linux-cluster] Multicast



Fajar A. Nugraha wrote:
Patricio A. Bruna wrote:
Hi,
Does cluster suite use Multicast in Red Hat 5?
If is so, how can i test my Switchs allow multicast traffic?

The switches that I tested allow multicast traffic by default.
You can test it by running some programs that uses multicast address, like :
- ping 224.0.0.1. Note that by default RHEL ignores broadcast pings, so
Regarding the **IANA Guidelines for IPv4 Multicast Address Assignments (**http://www.rfc-archive.org/getrfc.php?rfc=3171),
using some 224.0.0/24 based addresses will bypass  some multicast mecanisms.

The 224.0.0/24 addresses are dedicated to the local network routing messages meaning all ports of your switch will receive this traffic. But for the others multicast addresses, 3com/cisco and most of high end switches need to be configured to do the routing.

I mean you can find the "snooping" and the "querier/query" options in the multicast's switch configuration. Regarding the configuration, the mulitcast will works or not.

Snooping Off: all multicast traffic works
Snoop On: query off: Mcast is not working except for 224.0.0/24
Snoop On, query on: all multicast traffic works

This have been confirmed on a 3com 3870 switch. Its default configuration is set on "snoop on/query off". In such configuration, you must enable the "query/querier" option at least on a switch to make the multicast working.

So pinging 224.0.0/24 could generates some false positive results because in some configuration 224.0.0/24 could works whereas all the other multicast adresses are not.

On some low & middle end switches (dell etc..), activating the snooping enable the "querier" at the same time so this situation doesn't exists.


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