Network Interface stops working - how to restart

Hello Group,

every couple of weeks the NIC in my server stops working: No network  
connection possible.
On the console I can ping "localhost" and the assigned IP-Number  
192.168.1.4. When I attempt to ping the router / switch, to which the  
server is connected, I receive continuous errormessages:

ping: sendto: Host is down
when the interface is up or

ping: sendto: Network is down
when the interface is down

"ifconfig ex0" shows a perfectly operational interface, it can actually  
sense and display media-status when I dis- and reconnect the cable. I can  
change the interface parameters, including UP and DOWN, but not transmit  
or receive any data.

Likewise the server doesn't respond to any pings from the LAN.

"netstat" shows over 120 established tcp-connections, about 30 of them  
have a Recv-Q of about 30000, all other queues are 0. How can I terminate  
these connections?

I used to have a 3c905 NIC and replaced it with a 3c905b, both display the  
same behaviour.

When I tried to stop all processes, I noticed, that one process  
(presumably the one that last used the NIC eg. dhclient or mlnet etc.)  
will not terminate, neither in single user mode nor from the  
debug-console. Maybe it is stuck in the driver?

My only known workaround is to reboot the server, couldn't yet find any  
other way to restart / reset / unlock the NIC.

Can somebody please give me a hint, how to narrow down and possibly solve  
the problem?

Kind Regards
Thomas




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