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IPv6 LAN - Lesson one

Alastair Grant | Saturday 23 June 2012

IPv6 DHCP server - Tick

My Linux server has two dhcpd settings, the standard one and a dhcpd6.conf. Seems that they run on the same executable just different instances. I'm unsure yet if you can run everything from one daemon.

Dishing out IPv6 addresses from DHCP is pretty much similar to IPv4 and there are plenty of how-tos on the net. Getting Windows to ping back is a whole other ball-game.

My Linux devices all talked fine, but Windows would produce a "General failure" when trying to ping, despite successfully acquiring a IPv6 address from my DHCP server.

The issue apparently is one of Router Advertising (RA). Whilst DHCP will dish out configurations for clients, it doesn't describe the network. For that you need RADVD, which will advertise routers - even if you're not routing anything you need this for Windows otherwise it will configure itself to a /128 prefix (same sort of things as 255.255.255.255 in IPv4) - i.e. it won't leave the machine.

Why does Windows do this? I'd imagine that normally if you didn't have any routers to advertise then you'd be using the link-local address. As it happens, I'm just playing with IPv6 internally so whilst I'm not routing I still want to try out configuring it etc.

Hope this helps.

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