Dropbear with reverse tunnel listening on local port still active after disconnect

Alexander Kriegisch Alexander at Kriegisch.name
Fri May 23 18:19:16 WST 2008

Hi dropbear developers!

I am sending a copy of a message previously sent to the OpenSSH support
address, because it affects both OpenSSH and Dropbear on different
platforms. Maybe you know what is happening here.

BTW: I am not subscribed to this list, please CC your answer to my
private e-mail address. Thanks.


Here is an issue I have with
  OpenSSH_4.7p1, OpenSSL 0.9.8g 19 Oct 2007
on Cygwin (WinXP Pro SP2, German version).

BTW: Strange enough, I have the same issue on my AVM Fritz!Box (mipsel
platform) using Dropbear 0.50 as an SSH daemon.

I use Bitvise Tunnelier in order to open an SSH connection to the target
system. I use several client-to-server port forwardings and also a few
server-to-client reverse tunnels. The latter are the problematic ones,
because whenever there is an unexpected disconnect (e.g. because of a
DSL reconnect), the sshd process listening locally on the reverse
tunnel's port at the target system does not go away. I can see that with
lsof or netstat. The problem is that the reverse tunnel's port is thus
blocked, which leads to reconnect errors in Tunnelier, because
consequently it cannot re-establish the reverse tunnel now.

Is there any way to make the sshd process "notice" the disconnect and
exit cleanly instead of continuously listening on a local port for a
reverse tunnel which has no client end anymore?

Thanks and regards
Alexander Kriegisch
Certified ScrumMaster

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