[tulip] Linksys NC/100 v2 and Multicast - firewall

[root]

Can igmp multicast messages cross a firewall? 

I am posting out of desperation. I have found little or no documentation
on linux sysctl parameters, but I am thinking my network cards may be
transmitting igmp group membership info, which confuses the network. My
setup is a home network.  The server/firewall is a cable-modem
connection with a Lynksys NC/100 v2 (eth1) and a 3Com (eth0) card, with
eth0 connecting to the cable modem.  My workstation uses a Lynksys
NC/100 v2 card also.  Both use the tulip driver.  I had no problems
until my workstation HD crashed and I reloaded Mandrake 7.2 on the
workstation.  Now, whenever the workstation is running, the cable-modem
connection slows to a crawl.  With tcpdump the following message seems
to appear whenever the workstation is up:

14:56:19.888304 nerd3-30-1-tyl.cox-internet.com >
reserved-multicast-range-NOT-delegated.example.com: igmp query [gaddr
reserved-multicast-range-NOT-delegated.example.com] [ttl 1]

I get the following multicast groups on the server:
# netstat -g
IPv6/IPv4 Group Memberships
Interface       RefCnt Group
--------------- ------ ---------------------
lo              1      ALL-SYSTEMS.MCAST.NET
eth0            1      ALL-SYSTEMS.MCAST.NET
eth1            1      ALL-SYSTEMS.MCAST.NET 


and the following groups on the workstation:
IPv6/IPv4 Group Memberships
Interface       RefCnt Group
--------------- ------ ---------------------
lo              1      ALL-SYSTEMS.MCAST.NET
eth0            1      ALL-SYSTEMS.MCAST.NET

There probably is no connection, but that at lease eliminates one rabbit
trail.

Thanks for any comment.