Telnet problem after update from 2.4 to 2.6 kernel - Networking

This is a discussion on Telnet problem after update from 2.4 to 2.6 kernel - Networking ; 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 ...

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Thread: Telnet problem after update from 2.4 to 2.6 kernel

  1. 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


  2. Re: Telnet problem after update from 2.4 to 2.6 kernel

    On Aug 12, 3:05 pm, "Jens Bretschneider"
    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


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