Putty/OpenSSH on Windows - Crash Port Forwarding

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Hi there,

I've got a Windows OpenSSH server behind a NAT DSL router and I'd like to
use Putty's port forwarding feature on an XP client trough the Internet to
reach a mail server that sits behind the NAT. The SSH connection is OK, the
port forwarding is working fine as I can telnet to the desired port (POP3)
but I can't retrieve my mails because the connection always crashes. Even
when I try to FTP to a server behind the NAT, I can successfully login but
then when I try to list a directory, the FTP connection freezes and a couple
of minutes later I receive the world famous time out message, Putty is then
in a strange state and I can't exit the terminal Window, I have to kill it.

To me, it looks like Putty can't handle the traffic being requested and
simply drops the connection. Anyone has ever deal with this problem, is it a
misconfiguration on the serverside ? I had the same problem when my SSH
deamon was running on a RedHat 8.0.

Thanks in advance for your suggestions and merry X-mas to all of you,

Re: Putty/OpenSSH on Windows - Crash Port Forwarding

Your post is a bit thin on detail -- useful would be the version of
PuTTY, the direction of the tunnel (I'm assuming local-to-remote), and
the exact text of the "world famous time out message", for starters.

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Note that tunnelling FTP is difficult because it opens multiple
connections. PuTTY has no special support for tunnelling it; you might
be able to point a SOCKSified FTP client in passive mode at PuTTY's
dynamic SOCKS tunnelling (haven't tried it), but normal port forwarding
certainly won't do the right thing.

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How exactly are you trying to "exit" the terminal window? What happens
when you try?

Are other aspects of PuTTY's UI (e.g., the Event Log) still accessible
(i.e., is it still running)? If so, PuTTY hasn't crashed; in this case,
does the Event Log tell us anything useful?

Note that PuTTY won't close the session if it thinks there are still
tunnelled connections open.

There is a known crash in remote-to-local port forwarding in PuTTY
0.56, which is fixed in the development snapshots, but this seems
unlikely to be what you're running into.

Re: Putty/OpenSSH on Windows - Crash Port Forwarding

Hi Jacob and sorry for the lack of details, here's the deal :

On the client (Windows XP SP1) I have Putty v0.58 and on my Windows-based
OpenSSH server(which is also an XP workstation with SP1 by the way), the
version is 3.8p1-1 20040709.

I noticed that my sshd_config file on the server side still had the
"AllowTcpForwarding yes" parameter commented out so I removed the # and
restarted the service but still...

Thanks in advance for your help,

Re: Putty/OpenSSH on Windows - Crash Port Forwarding


  Richard Silverman

Re: Putty/OpenSSH on Windows - Crash Port Forwarding

Thanks for the link Richard, I've now determined that my NAT router doesn't
allow more than 1492 bytes packet so I'll lower the MTU and do some more

Merry X-Mas,

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