PPPoE misbehaving

[astrogeek@dork.com]

I recently had ADSL service installed, and I have had some strange problems with it connecting to certain WWW sites.  For example: http://tempo.gsu.edu, http://www.mbnanetaccess.com, http://www.aol.com, http://http.us.debian.org(!).  Sending email has also stopped working.

Almost everything else works fine.  What happens is the host is looked up, contacted, I receive a reply, then it stops at "transferring data".  The email messages all time out.  I can receive email directly, but not send it using exim now.  

I'm using the pppoe package from Potato.  The machine in question does ipmasq for a couple of Linux machines, these sites (and a few others) fail on every single machine including the one connected directly to the internet.  What I find to be really strange is that these sites work when I fall back to using the old dialup on the same machine, including on the ipmasq'ed machines.  So I figure I must have something set up wrong, but I'm at a loss as to what it might be.  I tried setting the MTU and MRU to 1500 with the same results (and a slight drop in transfer speed).

Here's what the net looks like from the ipmasqing machine (lo left out):

***
eth0      Link encap:Ethernet  HWaddr 00:50:BA:DE:3D:3D  
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:6659235 errors:0 dropped:133 overruns:0 frame:18
          TX packets:3829180 errors:0 dropped:0 overruns:0 carrier:0
          collisions:759 txqueuelen:100 
          Interrupt:10 Base address:0xfee0 

eth1      Link encap:Ethernet  HWaddr 00:A0:CC:D2:2D:B3  
          inet addr:192.168.1.1  Bcast:192.168.1.255  Mask:255.255.255.0
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:3818513 errors:0 dropped:0 overruns:0 frame:181
          TX packets:6638415 errors:145 dropped:0 overruns:4 carrier:141
          collisions:430178 txqueuelen:100 
          Interrupt:9 Base address:0xff00 

ppp0      Link encap:Point-to-Point Protocol  
          inet addr:remote.ip  P-t-P:207.69.62.1 Mask:255.255.255.255
          UP POINTOPOINT RUNNING NOARP MULTICAST  MTU:1500  Metric:1
          RX packets:2206279 errors:0 dropped:0 overruns:0 frame:0
          TX packets:1346162 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:10 
***

Thanks for any help, this has had me confused for days.  I'd like to try 2.4's kernel-based PPPoE with the hope that it's the software doing this, but not being familiar with netfilter is stopping me at the moment.

Andrew W.