July 9, 2010

251 words 2 mins read

IPv6: Getting functional DHCPv6 and Route Advertising together

If you’re not into IPv6, but you’re a networking person — you may want to avert you eyes.  This next piece of information is going to cause you pain:

DHCPv6 does not support/allow you to send default gateway.  This is “by design”.

Does your brain hurt yet? I know mine did when I first found this out.  This seems to be the most bass-ackwards thing I’ve ever heard of, but then again IPv6 is different.  I’m sure there is logic behind this decision, I just don’t understand enough of the details of IPv6 (yet) to comprehend that logic.

What does this mean for you? In short: You need both DHCPv6 and route advertising.

I wrote up the original set of instructions on

the IPv6 Wiki in a little more verbosity than I’m putting here.  Check out the wiki entry for full details.  The short version is as follows:

  • apt-get install dibbler-server radvd
  • Configure /etc/dibbler/server.conf with your subnet (/64) information
  • Configure /etc/radvd.conf with your information —  add “AdvManagedFlag on”
  • Restart both radvd & dibbler-server
  • Check /var/log/syslog and /var/log/dibbler/dibbler-server.log for output

At this point, you should be able to drop any DHCPv6 compatible machine (note: Not OSX) on your network.  If everything is setup correctly on Dibbler, Radvd, and your IPv6 routing, you should be good to go. Note: The radvd line “AdvManagedFlag on” is critical.  Without that, the client machine will receive a route advertisement and stop listening for DHCP.  Very odd, but IPv6 likes to keep us network guys in jobs.