Last Sunday one of our Cat6500 ( SW1 ) reboot due to electronic maintenance. After this switch up, some strange was happening.

1.Totally we have 4 Cat6500 switches, these switches connected via L2 EtherChannel with 802.1q enabled.

2.Both the SW1 & SW2 have L3 & L2 VLAN72 and used hsrp. these switches still have many other L2 & L3 VLANs.

3.There are many servers in VLAN72. for example : server A & server B. all of the servers connected to L2 VLAN 72 at another 2 Cat6500 switches : SW3 & SW4. Almost all of servers connected to SW3 switch.

4.I tried to ping server A from both SW1 & SW2 switches, the server A could reply successfully, but ping to server B failed. I used Sniffer to capture all traffics for VLAN72, while ping to server B, the SW1 & SW2 had not generate ARP request packet for server B, also when I execute debug arp, no arp request sent for server B, so no ARP & CEF adjacency entry for server B found in SW1 & SW2.

5.I also used another PC in VLAN 72 to ping to server A & B, both server A & B can replied ARP and ping packet.

6.If I create static ARP entry for server B at both SW1 & SW2, ping from SW1 & SW2 to server B success, both CEF adjacency table and arp table appear.

7.There are many servers have this problem, not only server B.

8.All switch CAM table was correct.

I upgrade SW1 & SW2 IOS to 12.2(18)SXF15a yesterday, but the problem still exists.... Please help !!!