All things related to multicast

[Alan Crosswell <>]

I've been looking at IGMP snooping behavior of a couple of vendor's switches (HP 
Procurve 2626 and Cisco Catalyst 3750).  See http://www.columbia.edu/~alan/igmp. 
 Some of the questions that are raised there are:

   1. Will HP be making IGMP v3 snooping work correctly on the 2626? When?
   2. Does IGMP v3 snooping work correctly on other HP ProCurve models?
   3. Why do both the HP and Cisco flood the group-specific query out all 
ports? Shouldn't this only go to the ports currently joined to the group? Does 
this matter?
   4. Why does the Cisco pass along all v3 host membership reports instead of 
just the one needed to keep the router happy? Does this matter?
   5. Why does the Cisco spoof an IGMP v2 Leave Group message toward the router 
when in IGMP v3 mode?

I'd appreciate feedback, corrections to my analyses (which use tcpdump traces 
which are included) suggestions for improvements, etc.

/a