Very Computer

One segment of this network has two different subnets assigned to it,
so that traffic between the subnets has to go through the router at
the common FastEthernet interface. I know this isn't ideal, but it's
part of a workaround for another problem we can't seem to solve any
other way.

Whenever a large amount of traffic (hundreds of megs) passes through
the router (from the FastEthernet port to an Ethernet port, or into
the FastEthernet and back out again), the packet loss shown by the
ping scripts increases dramatically, sometimes reaching as high as
12-15% in a single set of 100 pings.

On the router that has the two different subnets out one FastEthernet
port (a 2621 with a 1-port Ethernet card), none of the interfaces are
showing any input or output drops. The 'show buffers' command shows
some failures, but these aren't increasing terribly much over time.
There are quite a few collisions on the Ethernet port, usually
totalling about 6-9% of packets output. In times of high traffic,
throughput for other data streams is noticably reduced. In the output
of 'show process cpu,' the totals at the top seem kind of high (to me
at least), for example, five seconds: 38%/16%; one minute: 22%; five
minutes: 20%. The other figures in the list below that don't really
seem to change much from more idle times.

The problem actually was worse, and adding 'ip route-cache
same-interface' to the FastEthernet port made things a little better,
but the problem is still there.

Do we need a new router? Maybe more memory for the current one (it
seems to usually have 800k - 1.2mb free at any one time)? Do we need
to tune the buffer settings?

Thanks!

--Steve

You also need to be careful when going from a fast port to a slower
port.  If you are using fast switching, the faster port can over stuff
the slower port and this will result in lost or corrupted packets.  You
might want to implement weighted fair queuing to prevent packet
corruption - make sure the output buffer on the slower port is larger
than the input buffer on the faster port.

--Tony

The major part of this network is several Cisco routers connected to a
Catalyst 3516 Ethernet switch. All of the routers have little or no
input or output errors, which do not increase much over time. The
switch, however, shows many input errors on almost all ports that are
in use. These increase quite a bit over time (one increases 4000-5000
errors an hour). Most are frame errors. One port that's connected to a
Sun workstation shows no input errors, but many output errors. What
might be causing this?

*********** Remove the REMOVE if emailing me directly **************
Due to the volume of email that I receive, I may not not be able to  
reply to emails sent to my account.  Please post a followup instead.
********************************************************************
Hansang Bae        Director of Network Operations, Eastern Region  

Specializing in Network Design/Troubleshooting and Protocol Analysis
********************************************************************