I have 2 new Windows 7 home laptops (Toshiba Portege z835-p330). I am using the wireless adapter to connect to the LAN. Both laptops can ARP and receive MAC addresses for other LAN devices (gateway, printer, XP and Vista PCs), but the same LAN devices cannot ARP and resolve MAC addresses from either of the Windows 7 laptops. For example if I ping an XP PC from Windows 7, here is the ARP request and response as captured in wireshark: Request from W7: 9 6.011221000 74:e5:0b:79:ea:c6 Broadcast ARP Who has 192.168.125.12? Tell 192.168.125.103 Response from Dell XP: 10 6.011238000 Intel_6d:ab:79 74:e5:0b:79:ea:c6 ARP 192.168.125.12 is at 00:07:e9:6d:ab:79 But the other way does not work... Request from Dell XP to the Toshiba laptop: 15 7.515272 Intel_6d:ab:79 Broadcast ARP Who has 192.168.125.103? Tell 192.168.125.12 (no response) Retry 5 seconds later: 23 12.517446 Intel_6d:ab:79 Broadcast ARP Who has 192.168.125.103? Tell 192.168.125.12 The problem exists with other OS versions and devices. Here is a dlink device trying to resolve the MAC address: 17 9.005688 D-Link_4b:80:07 Broadcast ARP Who has 192.168.125.103? Tell 192.168.125.2 I googled, but found no solution (but plenty of similar sounding problems): I have tried: 1) completely dropping the firewall on the W7 pc 2) unselecting IPv6 under the properties of the wireless adapter 3) removing Norton firewall / virus software 4) enabling gratuitous ARPs (although it should not apply) 5) calling Microsoft (because windows is OEM they said contact Toshiba) 6) calling Toshiba (got not so technical rep. who ultimately hung up on me [hopefully it was an accident]) Thanks in advance. PacketWatch(er)

PacketWatch wrote: I have 2 new Windows 7 home laptops (Toshiba Portege z835-p330).  I am using the wireless adapter to connect to the LAN.  Both laptops can ARP and receive MAC addresses for other LAN devices (gateway, printer, XP and Vista PCs), but the same LAN devices cannot ARP and resolve MAC addresses from either of the Windows 7 laptops. For example if I ping an XP PC from Windows 7, here is the ARP request and response as captured in wireshark: Request from W7: 9    6.011221000    74:e5:0b:79:ea:c6    Broadcast    ARP    Who has 192.168.125.12?  Tell 192.168.125.103 Response from Dell XP: 10    6.011238000    Intel_6d:ab:79    74:e5:0b:79:ea:c6    ARP    192.168.125.12 is at 00:07:e9:6d:ab:79 But the other way does not work... Request from Dell XP to the Toshiba laptop: 15    7.515272    Intel_6d:ab:79    Broadcast    ARP    Who has 192.168.125.103?  Tell 192.168.125.12 (no response) Retry 5 seconds later: 23    12.517446    Intel_6d:ab:79    Broadcast    ARP    Who has 192.168.125.103?  Tell 192.168.125.12 The problem exists with other OS versions and devices.  Here is a dlink device trying to resolve the MAC address: 17    9.005688    D-Link_4b:80:07    Broadcast    ARP    Who has 192.168.125.103?  Tell 192.168.125.2 I googled, but found no solution (but plenty of similar sounding problems): I have tried: 1) completely dropping the firewall on the W7 pc 2) unselecting IPv6 under the properties of the wireless adapter 3) removing Norton firewall / virus software 4) enabling gratuitous ARPs (although it should not apply) 5) calling Microsoft (because windows is OEM they said contact Toshiba) 6) calling Toshiba (got not so technical rep. who ultimately hung up on me [hopefully it was an accident]) Thanks in advance. PacketWatch(er) Most probably that is an issue with your WLAN access point. I have similar issues from time to time on my home network. In my case it always comes to the point, that the arp cache of the access point is incorrect. In those cases I have to reboot the access point to get things working. But if you have an access-point where you could clear the arp-cache without reboot, that should suffice. Wolfgang

Wolfgang, You are exactly right. Something about the wireless L2 switching was screwy. A reboot seems to have fixed it. What threw me was that the problem only affected both new W7 laptops (across several weeks / reboots) but nothing else. Also the W7 PCs always work fine to/from the gateway (different device than the wireless access point), and if the MAC table on the wireless L2 switch was wrong, then why would any frames make it to the W7 laptops? Oh well. I guess it can fail any way it wants... I felt like the problem must be simple, and I now feel foolish for not performing more basic troubleshooting steps... Many thanks for helping! PacketWatch(er)