MPICH-GM and iptables

Hi:

I've compiled MPICH-GM version 1.2.6..14b with GM version 2.0.21. The OS
is Fedora Core 3 with the 2.6.11-1.35_FC3smp kernel. I've been testing
MPICH-GM with the simple example routine hello++ installed in
/opt/mpi/examples.

When I run the routine using processors on the local node, the program
executes fine.

When I run the routine using processors on different nodes, the program 
hangs indefinitely and exits after 5 or 10 minutes with a "failure to 
connect" error.

If I turn iptables off ("/etc/init.d/iptables stop") and try hello++ with 
processors on different nodes, the program executes fine.

Iptables appears to be the problem. Does anybody have a working iptables 
rule that lets MIPCH-GM communicate?

Thanks!

Dan Strahs