Linux Server Hacks, Volume Two

Hack #21. Integrate DHCP and DNS with Dynamic DNS Updates

Assign dynamic hostnames and IP addresses, and update your DNS server to reflect changes with no administrative intervention or scripted hacks.

If any two services are begging to be integrated, it's BIND and DHCP. Dynamically assigning IP addresses with DHCP isn't so useful if it makes your DNS zone information obsolete! Imagine if all of your configured printers got dynamically assigned IP addresses from your DHCP server. The next time your default printer got a new IP address from the DHCP server, addressing that host by name could return an unexpected result from DNS, because they're not in sync. Where your print job winds up could be anybody's guess.

With older versions of the ISC DHCP server and BIND, this problem was solved in one of two ways. First, you could just tell your DHCP server to statically assign addresses to your hosts [Hack #20] . This is still a useful solution to the problem, especially if the DHCP server delivers information besides an IP address, such as which NTP servers and NIS servers to use. The second option is to grab a tool (or script one yourself) to perform DNS updates.

In more recent versions of DHCP and BIND, both services support a mechanism for performing dynamic DNS updates (defined in RFC 2136), whereby an authorized user can add and delete records from forward and reverse zone files. Recent versions of DHCP also support a more flexible mechanism for deriving a dynamic hostname from an ...