in-addr.arpa traffic

[vtwintiger]

I have a DGN3500 router (is there a better sub-forum to use??) connected to my Win2003 server. I recently noticed traffic going to and from the server and <local IP address in reverse direction>.in-addr.arpa. netstat shows something like:
ServerBox:netbios-ssn 100.1.168.192.in-addr.arpa

Looking at the packets shows the ARP request going from the router (192.168.1.254) to a machine on the LAN (server or workstation) and then back to the router.

Any idea what is going on? I don't know if this is something the router is initiating or the server is somehow triggering it.

Thanks,
Justin