Yes, please add the IAID field and I'll be glad to do the testing. As I say, I'm currently testing against an MS DHCPv6 server and I think there is an inherent incompatibility between the two distributions which may or may not have to do with the server receiving FQDN and vendor class options from the client. I'm using Wireshark to sniff and I know the Solicit message is being sent. I've already tested the DUID and IAID functionality with FreeBSD clients and I know those fields are showing up in the right places in the Solicit. But the MS server does not Advertise in response. At least, no Advertise shows up in Wireshark as it does when Solicited from a Windows client. Strangely, though, the DHCP statistics displayed by the MS server always show an equal number of Solicits and Advertises. The log file generated by the MS server only shows incoming messages (Solicits and Requests), which is equally bizarre. Sounds like a firewall issue, right? I disabled it on both machines with the same results. I have to admit, I'm stumped for now. If anybody has any ideas, please let me know. I had hoped to rule out the FQDN-and/or-vendor-class issue by spoofing a Microsoft vendor code and sending the correct FQDN. I think the ISC client does have this functionality, but then I can't use pfSense as the firewall, which is a deal-breaker.