TCP differences in 7.2 vs 7.1

[David Samms]

After upgrading to 7.2 (amd64) some customers complained of very poor 
bandwidth.  Upon investigation all the effected customers were ATT DSL 
clients located all over the USA, not in a single city, nor were other 
ISPs effected.  The server is a Supermicro with  dual (quad core) 
processors with a single Intel fxp network card on a 100mbit connection. 
  Kernel is GENERIC for both 7.1_release and 7.2_release.  Normally a 
client can max out their download connection, but for ATT DSL customers 
the transfer rate would be about 5-10KB/s even though the server and 
client where both idle.

Repeated tests were done, from multiple clients in different 
geographical locations.  The problem manifested itself regardless of 
whether ftp, http, smtp, pop, or scp was used, and regardless of the OS 
of the client.  Believing it to be a routing issue we changed the route 
  and even changed the local router the server is connected to so that a 
different NIC port would be used to talk to ATT DSL customers, but no 
change in performance.

Turns out it is somehow related to differences in FreeBSD 7.1 and 7.2. 
If I boot the same server with 7.1, all clients work as you would 
expect.  But, if 7.2 is used all clients with the exception of ATT DSL 
clients would work normally, ATT customers would be limited to 5-10KB/s.

I have no reason to believe there is anything wrong with the ATT DSL 
network, it just happen to be effected by whatever causes the problem.

Any theories?

A special thanks to cybercon.com tech support for being so helpful.  If 
you need a data center, they have good tech support.