Question : 3Com Multicast issue across switches 4200G/4250T

Having some fun and games with multicast....

I have a business critical application that requires multicast to communicate with around 150 clients.  Originally, I had the server that is generating the multicast connectedto an unmanaged gigabit switch. Workstations were connected to 3Com 4500T managed switched (with IGMP Snooping enabled), which in turn connected to the unmanaged core gig switch.

Everything worked just fine.

The unmanaged switch dies on me.. so in the spirit of upgrade, I replaced it with a new 3Com 4200G gigbit managed switch.  IGMP snooping was enabled, and the workstation switches hooked up it.  Network works fine... but we started seeing lots of 'missed' multicasts causing our app the explode!  We temporarily switch ed our app o TCP broadcast mode - but are now drowning under the extra weight of packets so need to fix the multicast.

Testing using a multicast testing app seems with clients on a number of switches shows some interesting behaviour... packets seems to get delivered as normal... but then all the clients on one of the switches stop getting any packets for a while.  I don't think it's necessarily the same switch failing all the time.

Now I'm confused - if multicast works most of the time - what would cause it to keep stopping????

For clarity here is a pic of the topology... http://www.dropshots.com/photos/267328/20070614/b_182714.jpg
Using the testing tool I'm using - PCs on other switches continue to receive packets, whilst the ones on a particular switch just stop completely for maybe 10-30 seconds at a time...

Anyone offer any nuggets of help??????

Answer : 3Com Multicast issue across switches 4200G/4250T

>Now if it was a cable or loading issue or CPU issue - surely it would be more random.
   Yes that's what I'd expect also.
   
Any errors or warning signs showing on ge1/0/1?  Anything different about this port's config or what's connected to it?  How's CPU usage when the outtages occur?  If this switch is logging errors/warnings to a syslog server or SNMP monitor, anything unusual being logged?

cheers