[lug] Connection problems from Europe

[Jeff Schroeder]

Hey all--

I don't know what to make of this, so I figured I'd post a quick note to 
the group to see if anyone is experiencing the same problem, or can 
shed some light on what might be happening.

I'm running a few web sites out of Boulder, and from where I sit 
everything looks fine.  However, some users in Europe are unable to 
access the sites at all.  They can get to other sites in the world, and 
they can even get to other sites on the *same* server... but it seems 
like certain IP's are simply not working.

In particular, a user in England is able to see the site 
http://test.sketchup.com (204.144.129.176).  However, he isn't able to 
see http://www.sketchup.com (204.144.129.175) which is running on the 
same server.

Another user in the Netherlands has the reverse situation: he can see 
http://www.sketchup.com but not http://test.sketchup.com.

Both users can see http://www.bitrelay.net (204.144.129.168), which is 
obviously on the same subnet but a different server.  And neither can 
see http://www.doublearon.org (204.144.129.166), which is on that 
server as well.  I should point out that both users are network-savvy 
and are using different ISPs and OSes, so it's unlikely to be user 
error.

All in all, there doesn't seem to be a pattern to the madness.  Several 
other European users have the same problem, but in different 
combinations.  Note that tests throughout the United States-- from CA 
to NY-- indicate no problems whatsoever.  It's only these European 
users having issues.

I can't help but think there's something odd going on with my firewall 
(iptables, doing masquerading), but the firewall has been running 
smoothly for years and hasn't been updated or otherwise changed 
recently.

Does anyone have experience with random but consistent network problems 
like this?  Is there anything I should try in order to eliminate 
variables?

TIA,
Jeff