[Xorp-users] help me understand 224.0.0.22

dave dave at fishherder.dyndns.org
Mon Jul 28 10:36:46 PDT 2008


I'm relatively new to multicast networking and IGMP, so I apologize in
advance if my question seems obvioius.

>From RFC 2236 section 9

9.  Message destinations

   This information is provided elsewhere in the document, but is
   summarized here for convenience.

   Message Type                  Destination Group
   ------------                  -----------------
   General Query                 ALL-SYSTEMS (224.0.0.1)
   Group-Specific Query          The group being queried
   Membership Report             The group being reported
   Leave Message                 ALL-ROUTERS (224.0.0.2)

I interpret this as meaning that multicast processes have 3 destinations
to send IGMP messages to : all-systems, all-routers, and the desired
group address.

So what is the IGMP group addr (224.0.0.22) for?  What problem does it
solve that isn't addressed by the table above?  How important is it that
I allow this group in my security policies (firewalls, etc)?

Thanks in advance
- Dave



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