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Linux dhclient not registering IPv6 hostnames

Alastair Grant | Sunday 2 June 2013

I am not sure if this is a recent thing, but my openSUSE 12.3 boxes were not registering their hostnames in DNS. I, as many only allow the DHCP server to update DNS. The idea is that the client includes it's name in the initial DHCP request.

Whilst this works for IPv4 addresses, IPv6 wasn't.

The ISC dhclient program is what handles IPv6 DHCP (which is optional as IPv6 can auto configure). In openSUSE, YaST allows you to define the hostname to send to DHCP - but for some reason this doesn't work with IPv6. To fix it I manually updated the /etc/dhclient6.conf file with the line:

send fqdn.fqdn [hostname]

. Whilst this field can accept the entire fully qualified domain, it is also allowed to just be the hostname. Using just the hostname allowed my DHCP server to assign the appropriate domain name.

I also had to delete the file /var/lib/dhcp6/dhclient6.eth0.lease file, which holds details of the last IPv6 address given to the device. Otherwise dhclient was only confirming it's address and not requesting one. Without requesting one the hostname wasn't being sent.

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