[Udpcast] udpcast fails to multicast on 3Com switch

Andrew Cameron ACameron at vtlegalaid.org
Wed May 18 22:56:34 CEST 2005


  Here is my scenario. Clients A and B can succesfully be cloned from a
server running udp-sender when connected together via a hub. Either one can
also be successfully cloned as the only client to the server when connected
on the switch (as I understand it, this scenario is actually unicast, not
  When attemping to clone clients A and B on the switch simultaneously,
Client A writes:

udpreceiver for /dev/hda2 at on eth0
received message cap=00000019
connected as #0 to
listening to multicast on
and then writes nothing else. Client B is similar.

The server writes numerous lines like this:
Timeout notAnswered=[1] notReady[1] nrAns=0 nrRead=0 nrPart=1 avg=65625

After what seems like a couple of minutes, the clients drop off and then the
server stops.

We are using a class B subnet which initially gave me problems, but after
specifying the broadcast address on the DHCP server I can confirm the
clients and server are all using a bcast address of

We are using a 3Com 4226T switch and in the list archives I see several
references to problems with 3Com switches and IGMP. I have disabled IGMP
querying and snooping, and disabled broadcast storm control. Flow control
can be specified per port - so for the 3 ports that these machines are
connected to, I've disabled flow control, disabled auto-negotiate, and set
to 100Mbps full duplex. (There are other active ports in use on the switch
and I've left those on auto-negotiate with flow control.)

Does anyone have some advice?

Thanks for your time,
Andrew Cameron
Systems Administrator
Vermont Legal Aid, Inc.

More information about the Udpcast mailing list