I am having an issue with an Ethernet Shield on an Uno not responding to ARP requests. I have verified the MAC and IP addresses are unique and correct and on the same subnet (no router involved at all). The ethernet 'link' and '100Mbs' LEDs are lit. And I can see the activity LED on the Ethernet shield flash when the ARP request is sent. I have tried this through a switch, and point to point with a crossover cable, with no luck. I have sniffed the segment and I see the arp request being sent, but no response from the ethernet shield.
Is there something special that needs to be done for the shield to reply to ARP requests?
Any suggestions would be appreciated.