My Catalyst6509 have one VLAN72, and there are some servers in VLAN72, server A IP address is 10.100.74.5, server B IP address is 10.100.74.30. I tried to ping server A, the server A could reply successfully. But if ping to server B, no replied from server. I used Sniffer to capture all traffics for VLAN72, while ping to server B, the Catalyst 6509 had not generate ARP request packet for server B, so no ARP entry for server B found in Cat6509. I also used another PC in VLAN 72 ( PC C, IP address 10.100.74.100 ), both server A & B can replied ARP and ping packet. Can you give me some advise to resolve this problem?