DHCPv6: passing delegated prefix to local RA

caw asked:

I currently have an Airport Extreme as my home office firewall. In addition to handling IPv4 NAT, my ISP (Comcast) delegates an IPv6 prefix to the Airport, which in turn assigns the delegated prefix to my LAN interface and sends the appropriate route advertisements.

I’d like to replace the Airport with a small Linux firewall – the NUC with a second ethernet interface is looking quite intriguing – but I’m having trouble determining whether the IPv6 behavior can be replicated. My basic questions are:

  • Can ISC’s DHCPv6 client accept a prefix delegation, or only host IPv6 addresses?
  • If the above is true, can the DHCPv6 client assign the received prefix to a different interface? Does the client support “on commit”, or is that only supported on the DHCP server?

My answer:

ISC DHCP certainly will request a prefix delegation from your ISP if you ask it to, but it won’t actually do anything with it beyond logging it somewhere. Nor will any other DHCP client.

If you really intend to build your own router, you’ll have to write your own scripts to determine the prefix that was delegated, set up static routes, and configure your router advertisement daemon and/or DHCPv6 server on your LAN.

If you want an example, OpenWrt beginning with Barrier Breaker has already done this and you may be able to reuse some of their work.

For a home office I wouldn’t really bother with this, and just use something off the shelf that has proper IPv6 support…like your Airport Extreme.

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