I have a college residential lan whose archetecture hasn't changed for several years that has been having trouble for the last week or so.
It consists of multiple stacks of 3750's that aggregate to a 3550 as the last stop before going to a 3750 layer 3 switch acting as the gateway.
The symptom is lost packets to the gateway. It varies from <1% to as much as 20% during any time tested. Although it has at times seemed worse at night, that is _not_ always the case. Just this morning at 7AM (very low usage) I was getting 4% loss to a test box I have in one of the halls. At the moment (10AM) its zero loss in a 10 minute test.
The resnet has about 650 hosts on it, and the trunks also carry the wireless lan traffic which has maybe another 200 or 300 known Mac addresses.
Traffic _within_ and between hosts on the same lan are not impacted at all.
All switches are running some recent variant of 12.2(25).
Over the last 6 days, I've check everything I can think of, even resorting to downgrade the firmware in the layer 3 gateway.
Oh, by the way, NO interface errors _anywhere_.
If anyone can think of something to look at that I haven't already, I'd sure appreciate it.