As part of my IPv6 self-education, I downloaded and installed the UTM 9-003 virtual appliance under VMware Workstation 9 on my PC. I put the first network adapter on a private virtual network (VMnet2) along with a 64-bit Windows 7 instance to act as a LAN client.
Everything went fine on the IPv4 side, and setting up static IPv6 addresses on the Internal and WAN interfaces also went without a hitch, but when I tried to set up IPv6 DHCP on the Internal network, I came to a grinding halt. The dhcp6 server was running, but it wasn't receiving any requests, so my client machine wasn't getting an address. I installed Wireshark on the client, and could see the dhcpv6 Solicit requests being broadcast, but for some reason they just didn't appear to be reaching the UTM.
After going over everything several times, and tearing out what remains of my hair, I decided, in desperation, to install another NIC and try setting up another IPv6 dhcp server. However, when I rebooted the UTM, I noticed that the new virtual NIC appeared to the VM as a virtual Intel E1000 NIC vs the preinstalled AMD interfaces.
So rather than try creating another IPv6 network, I simply moved the Internal network over to that Intel vNIC, and presto!, dhcp6 started to work exactly as it should - the Solicit requests actually appeared in the UTM log and were handled perfectly, so the client finally got the IPv6 address it had been requesting all along.
To summarize: it appears that there is some sort of incompatibility between the v9 dhcpd6 daemon and the default AMD virtual NICs installed on the virtual appliance image - a problem which is seamlessly resolved by replacing them with new Intel vNICs using the E1000 driver.
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