I am wondering if someone can help me with a strange layer 3 switching situation on my Catalyst 3750. It is my core switch and is configured with 2 Vlans - 1 server vlan and 1 workstation vlan. The workstations dhcp from a dhcp server in the server vlan. Occasionally a PC will boot up, get an IP address from the DHCP server, but not be able to communicate with the server VLAN. I look at ipconfig on the workstation and everything looks fine - subnet mask/default gw are both correct. From the 3750 I can ping the workstation successfully, but from a server pings are unsuccessful. I performed a network capture at the workstation side and found that when the workstation in question does an unsuccessful ping to a server, the ping reply from the server is actually seen in the capture, even though the PC doesn't get a successful ping reply in Windows. Upon looking at the ping reply a bit closer, it is being sent to the wrong MAC address. I finally stumbled on to the fact that occasionally workstations have IP conflicts when they boot up. When I look at the capture, sure enough, the 3750 is sending the ping replies to the MAC address of the workstation that had a conflict. If I do a clear arp on the 3750, pings start to go through again and the PC can communicate with the server VLAN. Now obviously IP conflicts are not good and that needs to get cleared up, but I'm very curious as to how the 3750 can successfully ping the PC with the right MAC address, but when the 3750 needs to route a ping request from a server to the workstation, it sends the wrong mac address. It's like the arp table is different for traffic originated from the switch and traffic routed through the switch.
Any ideas? Is there a "show" command other than show arp that I can look at to see what is going on b/c when I do a show arp when things are broke, the 3750 has the right mac address for the workstation.
We are pleased to announce availability of Beta software for 16.6.3. 16.6.3 will be the second rebuild on the 16.6 release train targeted towards Catalyst 9500/9400/9300/3850/3650 switching platforms. We are looking for early feedback from custome...