Windows – Cannot connect to telnet server

telnetwindows 7

So, I can't use telnet to connect to any server but it works fine from a different computer. It just says it can't connect. I tried the following things:

  • Disable firewall and AV protection. (Basically, there was no security feature left online)
  • Telnet is set to "Trusted" in my AV protection. (Kaspersky Internet Security 2011)
  • Using Putty to telnet, but apparently Putty's connection is also inhibited. (Says it can't connect to host)
  • Disabling the telnet client in Control Panel and then re-enabling it. (Windows 7 Ultimate)
  • hosts file is clean.
  • Checked for nasties using MBAM and KIS 2011 as well as going though my HijackThis logs, nothing found.

I can connect to the same machines/servers through the web browser, ping, tracert, etc. Only telnet seems to be blocked.

Any other thoughts?

Best Answer

Have you tried disabling the auto-tuning diagnostic in Windows 7?

netsh int tcp set global autotuninglevel=disabled

Microsoft Support KB article:

When the receive window autotuning feature is enabled, older routers, older firewalls, and older operating systems that are incompatible with the receive window autotuning feature may sometimes cause slow data transfer or a loss of connectivity.

The default auto-tuning level is "normal", and the possible settings for the above command are:

  • disabled: uses a fixed value for the tcp receive window. Limits it to 64KB (limited at 65535).
  • highlyrestricted: allows the receive window to grow beyond its default value, very conservatively
  • restricted: somewhat restricted growth of the tcp receive window beyond its default value
  • normal: default value, allows the receive window to grow to accommodate most conditions
  • experimental: allows the receive window to grow to accommodate extreme scenarios (not recommended, it can degrade performance in common scenarios, only intended for research purposes. It enables RWIN values of over 16 MB)
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