I've had a couple of machines (all in the same physical area) just lose their network connectivity. They can ping their gateway, but nothing beyond it. It appears as though the 'echo request' is actually getting off their subnet, but the 'echo replies' aren't getting back to them. Similar problem with the VOIP (separate voice vlan) -- you can hear them, but they can't hear you. If I statically assign a different IP in the same subnet, it works fine. I've also tried to change their VLAN assignment, still have the problems. So far it's happened to almost everyone in that area, at different times.
They're connected to a Cisco 3550, IOS 12.1. That is physically connected to another 3550 that's acting as the router (there's actually 2 core switches configured in a failover mode)
Anyone seen this before? Or have any troubleshooting steps or debug ideas?