I've got a packet loss problem I can't seem to figure out. On the
network in question, I've got several test scripts running. Each is
doing a hundred pings from a different point on the network every five
minutes to another host on the network (at least one hop away). No
matter where I start from or ping to, I see some amount of packet
loss, perhaps 5-10 packets in an hour. That's not a lot, I know, but I
don't see why we should be seeing any, except on rare occasions.
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
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?