Published Telnet Server Connection Hangs (Full Version)

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KevinSawyer -> Published Telnet Server Connection Hangs (7.Oct.2005 4:31:00 PM)

I have a brand new SBS 2003 Premium with SP1 (ISA 2004) and it works great. There's a Linux-based server within the internal network. I've created a publishing rule for inbound Telnet access to that Linux server and it works...until I do something that results in a burst of text being sent back to the remote client, then the connection hangs.

If I telnet into the Linux server from within the local network, everything is fine. If I establish a VPN connection to the SBS then telnet to the Linux server, everything is fine. It's only when I telnet via the publishing rule that connections eventually hang. If I list the contents of a directory that only had a few files in it, it works. If I list the contents of a directory with many files (and therefore a larger burst of text), the connection will hang every time.

When I watch the ISA logs, there is nothing out of the "denied" or "connection closed" when the hang condition occurs. The Linux-based server is RedHat 7.3 with all available patches/updates. Any ideas?


[ October 07, 2005, 04:32 PM: Message edited by: Kevin Sawyer ]

KevinSawyer -> RE: Published Telnet Server Connection Hangs (7.Oct.2005 5:37:00 PM)

Looks like we figured it out. The MTU on the Linux server was 1500. We lowered it to 1452 and now all is well. We needed to get it running quickly so I'm not sure what the max MTU could be without breaking it.

Since the MTU didn't break anything when we were using VPN or when we telnet directly from the SBS console, I can only conclude that the problem is within the ipnat.sys or other "router" code within ISA and/or Windows Server 2003. We found and reported a similar Microsoft bug in ISA 2000. Problems like this really make it frustrating that we don't have the source and can't fix it ourselves...but that's another rant.


denizyalcin -> RE: Published Telnet Server Connection Hangs (20.Feb.2006 5:52:05 PM)

Hi, I know that this is a very old thread but I've got a problem similar to this. I've the same setup as Kewin Sawyer and I managed to publish my Linux server, too. But my problem is that my client's connection dies when it isn't being used for a few seconds. When my client does continuously use the connection, there isn't any problem but when it stops using the connection for a small time it's being dropped. What can be the cause for this ?

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