We have a Netscreen router as the default gateway. I have a windows 7 machine in the network. I deleted the ARP cache on this windows machine using the command "arp -d". As soon as I did that, there was an ARP request from my windows 7 machine and I see that there are two responses from the GW (packet #1168 and 1170 in the below table).
1167 6.585819 Vmware_a9:70:dc Broadcast ARP 42 Who has 10.218.16.1? Tell 10.218.22.221 1168 6.588741 Netscreen_ff:50:01 Vmware_a9:70:dc ARP 60 10.218.16.1 is at 06:22:bc:ff:50:01 1170 6.590643 Netscreen_ff:50:01 Vmware_a9:70:dc ARP 60 10.218.16.1 is at 06:22:bc:ff:50:01
I tried out a different machine in a different network and found that the router responded with only 1 response per request (this router seems to be a Cisco router)
2698 15:58:09.094908000 Vmware_85:6c:cf Broadcast ARP 42 Who has 10.211.32.1? Tell 10.211.34.212 2699 15:58:09.096329000 Cisco_e0:3f:01 Vmware_85:6c:cf ARP 60 10.211.32.1 is at 00:00:0c:9f:f0:20
In both the cases, the ARP cache immediately had an entry for the default gateway.
What I cannot understand, is why the default gw is sending out two responses for one request?
Any pointers will be greatly appreciated.