Telnet problem after update from 2.4 to 2.6 kernel

Hi,

I'm working at an ISP and we're regularly running a perl/expect/telnet
script which connects to our customer's routers (CPEs) via telnet and logs
the output of some commands on that devices for configuration backup
purposes.

Now, after updating from an old linux with 2.4 kernel to a newer 2.6 one, we
notice that the telnet connection to one kind of our CPEs, Siemens EN5935,
slows down while responding to the commands more and more with every line
read from the CPE. Further tests showed the same problem with the Microsoft
Windows Telnet Client and with different versions of the telnet command on
2.6 kernel.

The affected cpes are connected via PPPoE, which has a MTU of 1492. Other
CPEs from Siemens from the same device series (e.g. EN5950, EN5851), but
connected with PPPoA with MTU 1500, do _not_ have these problems, even if we
set their MTU to 1492 too.

Any Idea what has changed in the tcp/ip stack from kernel 2.4 to 2.6 which
can cause these problems? I'm not a linux expert and have no clue where to
start...

Many Thanks!
Jens



Jens Bretschneider

On Aug 12, 3:05 pm, "Jens Bretschneider" <n...@jens-bretschneider.de>
wrote:

> Any Idea what has changed in the tcp/ip stack from kernel 2.4 to 2.6 which
> can cause these problems? I'm not a linux expert and have no clue where to
> start...

Try turning off SACK and see if that helps. Try turning off window
scaling and see if that helps. These are both controlled by files in /
proc/sys/net/ipc4.

DS