ARP Switches

Be aware though that manually setting addresses in the switch filter table means that port will only ever talk to the device you've specified. So be sure why you want to do this and keep records. Otherwise you'll be ripping your hair out months later trying to figure out why some ports on your switch aren't working. The only reason I can think of is security - manually setting the table prevents anyone wandering up and plugging a foreign device into your switch port (unless they can manually spoof the MAC Address, heh! heh!)

A slight correction is needed to what sreekumar said a few posts back. The ARP protocol is used to obtain the hardware (MAC) address of a known IP address, not the other way round.

Cheers.

Thanks Greenice for correcting me. You are absolutely right. RARP is used to obtain the IP address of known hardware address as used in DHCP. However, I've always wondered - when a DHCP server responds to an RARP request, does the layer 2 frame go as a broadcast or as a unicast directed to the host requesting IP address lease?

Client sends DHCPDISCOVER (Broadcast)
Server sends DHCPOFFER (Unicast)
Client sends DHCPREQUEST (Broadcast)
Server sends DHCPACK (Unicast)

For more detailed information see CCNA 3 and 4 companion guide third edition page 391.