Bizarre networking problems on sid

[James Wiggs <wiggs@wiggs.org>]

 Folks,

   I've got a really bizarre problem on one of my Sid boxes.  I have
two boxes on a private subnet behind a LEAF router box.  Both of them
have static IP addresses and are running Sid (fully up to date as of
last night).  One of the boxes is experiencing network problems where
it is incapable of connecting via certain protocols to certain hosts.
For example, using Mozilla on the box, it connects to www.google.com
and www.iso.org, but *not* to www.oasis-open.org or www.xml.org.  The
other box connects to all of them just fine.  The Mozilla status bar
just says "connecting to ..." and sits there.  It never actually
connects.

   As another data point, the "working" box can connect to the NNTP
server at news.rr.com, but the bad one can't.  The boxes have the same
/etc/hosts files, the same /etc/resolv.conf files, etc.  The output of
"netstat -rn" on both boxes is identical.  Both are using 3c905B net
cards.  Neither has any suspicious stuff in its "ifconfig -a" listing.
The working box is an Athlon, non-working box is a dual PII.  Can any
of you suggest a possible explanation for this?  How on earth can the
networking fail so *selectively* on the one box?  It sounds like a
firewalling issue, but neither box is running a local firewall.  The
firewalling is done at the router, which is almost completely closed
off.  I've *never* seen anything like this, and could really use some
help...

   Oh, yes: restarting networking and even rebooting the box have had
no effect on the problem whatsoever.

thanks,
Jim