Session resets

Hi.

 

I work at Novis Telecom, a Service Provider in Portugal and have a
strange problem in three clients that are using wtk. Check this please
to see if it has already happened somewhere or if someone has a hint on
how to solve it.

 

If the wtk emulator is run on machines in the same LAN than the server
or in a remote site connected by a dedicated circuit (PPP or
Frame-Relay), everything works fine. But the sites that have ADSL
circuits and are connected to the head-quarters via IPSec tunnels have
problems: sometimes the sessions fall and the users have to re-establish
it again.

 

And extra look at the traffic showed that are the PCs running wtk (not
the server) that send TCP RST packets, resetting the TCP session. It
happens with no apparent pattern, sometimes after an idle time and
others in the middle of a busy session.

 

The client's PCs have windows 98, ME and XP.

 

One of the first thing I suspected was a MTU problem because ADSL have
MTU 1492 bytes and the IPSec tunnel adds some overhead. But I see
over-MTU ICMPs from the server (probably MTU discovery, I can't confirm)
that are well answered by the router with a "Frag nedded but df bit set"
message. Apparently the server honours this message because it never
tries to send packet bigger than the MTU. But, nevertheless, are the
clients that reset the sessions...

 

I already tried to reset the df-bit, implement fragmentation but never
solved the problem.

 

As a proof-of-concept I changed the tunnel from IPSec to GRE (witch as a
larger MTU) and everything seems to work fine.

 

Help is really appreciated.

 

Thanks in advance

 

 

--

Telmo Oliveira

Client Network

* [email protected]

 

 

  <http://www.novis.pt/> 

 

A Novis recomenda-lhe: lembre-se da sua responsabilidade ambiental antes
de decidir imprimir este e-mail

Novis recommends you to consider your environmental responsibility
before printing this e-mail