[plug] port 22 opens and closes randomly?

[Rob Dunne]

Hi Pluggers,

I have a small server running Debian etch. It is actually a NAS
that has been flashed and had freelink installed
http://buffalo.nas-central.org/index.php/FreeLink_for_the_Linkstation_Pro
but I dont think this is relevant to this problem (but then, I
dont really know).

Sometimes it boots with port 22 closed so I cant ssh to it and I
cant mount it (SMB connection failed).  Sometimes it lets me on
for an instant ie

BUFFALO INC. LinkStation series LS-GL(IESADA)
root at LS-GL7D6:~#
root at LS-GL7D6:~# Read from remote host 192.168.1.101: Connection reset 
by peer
Connection to 192.168.1.101 closed.

sudo nmap  -p 1-2500 -O 192.168.1.101
All 2500 scanned ports on ls-gl7d6 (192.168.1.101) are closed

but a moment later

sudo nmap  -p 20-25 -O 192.168.1.101
Starting Nmap 4.20 ( http://insecure.org ) at 2008-02-24 19:45 EST
Interesting ports on ls-gl7d6 (192.168.1.101):
PORT   STATE  SERVICE
20/tcp closed ftp-data
21/tcp closed ftp
22/tcp open   ssh

so ssh port 22 is opened and closed seemingly randomly.

When this happens I have been able to get it back to the
emergency boot mode and then it back to FreeLink on the next boot. 
However for the
last 5 boots it has come up in the "no ssh" state.

What could do this? I have set the log level in sshd_config to DEBUG3
but I dont see anything helpful. Where else should I look for a clue?

Bye
Rob