Port forwarding problem with 2.5.1p2

Keith Wesolowski keithw at rightorder.com
Sat Mar 10 04:52:45 EST 2001


There appears to be a bug in 2.5.1p2 that is not present on 2.3.0p1.
The environment in question is Solaris, on either Intel or Sparc.  The
arrangement is as follows:

System bar forwards a port from itself to system baz by doing

su portfw -c 'ssh -2 -P -N -f -g -L 3333:baz:22 baz'

System foo, which can talk to bar but not baz, initiates an ssh
connection to bar port 3333, and is able to log in through that to
baz, which runs an sshd on port 22.

The problem is that this only works once.  After disconnecting from
baz, a subsequent attempt to connect in this manner causes an error
ssh_exchange_identification: Connection closed by remote host, and the
ssh process doing port forwarding on bar dies (it also gives a
message, Connection closed by remote host).  

Restarting the ssh port forwarding process causes it to work again,
once, and so on so that if I run the port forwarder in a loop, so that
when it dies a new one starts up, then connection attempts from foo to
baz alternate between error and proper functioning.

This did not happen with 2.3.0p1.  Further investigation reveals that
if baz is running 2.3.0p1 then it works regardless of the versions
that foo and bar are running.

Any ideas?  It seems likely that this is a bug, or at least an
undocumented behaviour change.  Thanks in advance for any help.

Keith M Wesolowski
Systems Administrator
RightOrder, Inc.

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