[c-nsp] router ethernet

[Ed Ravin]

On Thu, May 05, 2005 at 02:29:51PM -0400, Kern, Tom wrote:
> I have a 1700 router which is my internet router. it has a
> frame-relay serial int and an etherent int.
> About twice a month, the ethernet int dies. Actually, it says eth0
> up, line protocol up but i can't connect to the internal network
> from the router. I can however ping out on the frame.

I've had a similar problem with a Cisco 1750, currently running
IOS 12.1(24).  I'm just using the onboard Ethernet interface, and
every "now and then" (sometimes twice a month, sometimes every 3
months), the Ethernet interface appears to stop receiving packets.
We replaced the Ethernet cable, upgraded the IOS, swapped the router
with an identical unit, added more memory, smeared the entrails of
a sacrificed goat on the AUX port, all to no avail - it would still
happen from time to time.

When it's in this state, this command usually brings the port back to life:

   clear int FastEthernet0

Shutting and "no shut" on the interface usually work too.  Once or
twice I've reloaded the router, but that was before I discovered
that "clear int" works.  Haven't had to reload the critter for a while.

It appears that the interface just "goes to sleep" - no input packets,
no output packets.  ARP tables in both the router and the switch it
is connected to expire.  We have monitoring software that pings the
router every minute, so it's not provoked by inactivity.

I've been thinking of writing a batch job that runs "clear int faste0"
every 30 minutes, so if it happens again it'll probably clear up before
I get paged.  Can anyone see any downsides to doing that?