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I have a Windows Server 2008 R2 machine here that is just not responding to Neighbour Solicitation requests (the IPv6 equivalent of ARP). It can see the requests, it's just chosing not to respond to them.

Wireshark sees the following request:

758 7.414264 2a01:348:6:4a6:0:15:5da1:544 ff02::1:ff00:2 ICMPv6 Neighbor solicitation

The target is clearly defined as

Target: 2a01:348:6:4a6::5 (2a01:348:6:4a6::5)

And IPConfig shows a matching local IP address (statically configured in this case)

IPv6 Address. . . . . . . . . . . : 2a01:348:6:4a6::5

So I'm at a loss as to why it's not responding.

Any ideas where I can start checking?

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1 Answer 1

up vote 2 down vote accepted

Eck. Sorry I'm stumped too.

The only thing that pops to mind is the Firewall. The log should show any dropped packets.

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I'm such an idiot. I can't believe I didn't think to check the firewall logs. I can see it being dropped in there. Now to find out why. –  Mark Henderson Jun 20 '11 at 21:38
    
You probably know this but i'll repeat it in case someone else reads this. It's very important that you allow ICMPv6. ICMPv6 is critical for the proper functioning of IPv6, not just a "nice-to-have" like ICMPv4 was. –  Mike F Jun 20 '11 at 22:52
    
yep, totally understood. I still haven't figured out why they're being dropped, but ICMP is def. permitted. –  Mark Henderson Jun 20 '11 at 23:04
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