I'm not sure when this started, maybe with Snow leopard, but every once in a while my MBP is unable to communicate with either of my Windows PCs. If I run 'arp -an' on the MBP, I can see the MAC address of my PCs, but if I run arp -a on the PCs I don't see the MAC of the MBP. So I ran wireshark on the PC and 'tcpdump -i en1 arp' on the MBP (en1 is Airport) and while I see the PC broadcasting a who-has, I don't see them on the MBP side. I do see who-has requests on the MBP coming from my router, to which my MBP responds, just not from either of my PCs. If I disable and re-enable the Airport on the MBP communication starts working again, or I can enter in a static arp entry for the MBP on the PC. MacBook Pro5,5 <-> 802.11G <-> ActionTec MI424-WR C <-> CAT5 <-> Netgear FS116 <-> CAT5 <-> PC Any suggestions would be greatly appreciated.