In my catalyst 4506 switch some of the users loose their connectivity to the gateway in their pc for a certain period.If the ip is renwed in pc or the port is reseted in the switch then the pc will regain the reachabilty to the gateway.The lan connection is always showing connected even when it looses the reacability to gateway.The switching is running IOS 12.2(25)EWA7.I'm not seeing any loggs on switch also.
If the switch is also the default gateway and you are running HSRP this could be an ARP/CAM timeout problem. The issue is that the timeouts for the ARP entries (on the routing side) and the CAM entries (on the switching side) are different. The default CAM timeout for the MAC address is 10 minutes and the ARP entries is something like 60 minutes. The fix is to make them both the same. We change the ARP time to 10 minutes and this can be done using the command "arp timeout 300" on each VLAN interface. I don't know why Cisco doesn't make them the same by default. Resetting the port on the switch or renewing the IP on the client forces the switch to relearn the MAC in the CAM table. By setting the ARP timeout to same value as the CAM timeout, the routing side will ARP the address of the client which will have the side effect of the switching side to relearning the MAC in the CAM table.
You can verify this is your problem if pinging the IP of the client from the switch (or pinging the default gateway from the client, I can't remember which) also temporarily fixes the problem.