Windows 2008 ignores Gratuitous ARP requests

Solution 1:

After testing it does seem that Hotfix 2582281 fixes the issue. You can get the hotfix without having to pay support by using their hotfix request page.

I ran a test of this using arping and unpatched windows 2008 R2. I added a secondary IP, 64.34.119.80, to a machine with in the same network L2 segment. I then issued the following command from a different machine the network (sudo arping -U 64.34.119.80 -I bond0 -c1). Right after that, I pinged 64.34.119.80 from the windows box after seeing it recieve the arp in wireshark. I then applied the hotfix and repeated the test.

Also, it seems that the arping command needs to not use unicast MAC address but rather the broadcast MAC because this is the only type of GARP ignored from my tests.

Before the patch:

In this wireshark capture, the ping after the GARP request is not sent to the MAC Destination that the GARP came from, so you can see that GARP is being ignored.

After the patch:

In this test, after the patch, the GARP request seems to be honored as the ping is sent to the MAC address that GARP came from.

So from these tests it seems hotfix 2582281 fixes the issue of GARP broadcasts being ignored.

Solution 2:

When researching my own TCPIP problem just now, I stumbled across this very interesting Hotfix:

http://support.microsoft.com/kb/2582281

Cause:

This issue occurs because the TCP/IP stack of the application server incorrectly ignores gratuitous Address Resolution Protocol (ARP) requests.

This sounds an awful lot like what you're running into. And it's a brand new hotfix as well, released 7/22/2011, so wasn't around when you first ran into it.

Solution 3:

Try netsh interface ipv4 set interface x basereachable=y where x is the interface index and y is the ARP timeout in milliseconds that you want. Remember to do it from a command prompt with admin privileges!