Server process not closed after disconnect, problems with reconnect

[Alexander Kriegisch]

My setup:
  - Server (DSL/WLAN router running Dropbear sshd v2012.55)

      $ uname -mrsp
      Linux 2.6.19.2 mips unknown

      $ ps | grep dropbear | grep -v grep
       1673 root      1352 S    dropbear -i -R -a
      14826 root      1396 S    dropbear -i -R -a

  - Client

      OS: Windows XP Pro 64-bit
      SSH Client: Bitvise

As you can see, my Dropbear runs as root in inetd mode, permitting root logins (which is what I use) and accepting connections to forwarded ports from other hosts. I need this because my connection basically creates a few forward tunnels (client to server) to other machines behind the router as well as backward tunnels (server to client) to a few services on the client's network. So far, so good.

The DSL router gets disconnected once every night, reconnects within seconds and gets a new IP address, which is the usual thing in Germany for consumer-type ISP connections. What I expect to happen is that the dropbear process goes down, but in ca. 4 out of 7 days this does not happen. The main symptom is that the auto-reconnect for the SSH connection to the dynamic host name fails because ports on the router cannot be bound because they are already in use. When I check with netstat I can see that indeed all the listening ports for the reverse tunnels are still in use by the old Dropbear process which has not terminated. On a few days a week it works, but I do not know the circumstances or race conditions which cause this behaviour. So what I end up doing most of the time is log on to the router without the tunnels and kill the non-terminated Dropbear process blocking the listening ports. A few seconds later, the full-blown SSH connection with forward and reverse tunnels automatical
 ly reconnects and everything is fine for another 24 hours.

Now this obviously is ugly and unstable. Is there a way to make Dropbear understand it should terminate when the DSL connection is gone? Or is there at least a workaround by which I can check if the SSH process ist still alive? I thought that maybe I could try and connect to one of the stale reverse tunnels (localhost:someport on the router) in order to see if it is still functional, then kill the process otherwise, but I had difficulty doing so because a wget test does not work (I only have Busybox wget which does not have a time-out parameter).

Please ask for more information if this was too unspecific.
-- 
Alexander Kriegisch
http://scrum-master.de