DHCP addressing vs Static addressing for Servers

dhcpstatic-ip

I'm having a "lively" debate with a work associate about the reasons for or against using DHCP on servers in a network environment. The network environment in particular is a relatively small network, but in my experience it's always better to have servers on static addresses, especially for things like remote management, etc.

I looked, and could find any specific reasons for or against dynamic addresses assigned on servers so I figured I'd ask the crowd here.

My work associate argues for DHCP assigned server addresses for ease of management, and states if the addresses ever change you don't have to change the server IP manually. I'm dubious about this response.

For management purposes, this network being small, it's no big deal to change the IP of static devices since there's so few.

Any suggestions, ideas or comments?

Best Answer

While there are some server functions that must have locally defined IPs, I'm a huge fan of using DHCP for server addresses.

First, as others have noted, you can (and should) use DHCP to serve up static addresses. Assuming Linux, you want this in your dhcpd.conf:

host server {
        option host-name "server.example.com";
        hardware ethernet  xx:xx:xx:xx:xx:xx;
        fixed-address server.example.com;
}

And in your DNS zone file, assign an IP to server.example.com.

Pros:

  • The DNS zone file is now the 'one source of truth' for all IP assignments. Makes it easy to look for errors (duplicate IPs, typos), and ensures that everyone can find the server's IP address without error
  • Changes to network infrastructure can be propagated easily. Rolling out a backup DNS server? Just add it to the DHCP config file, and all systems will pick it up as they renew their leases.
  • Changes to the machine's IP and the machine's DNS entry can't, by definition, get out of sync. Moving a machine to a new subnet? Change the IP in exactly one place, and you're all set.

Cons:

  • You've added a significant point of failure. Mitigate that with backup DHCP server. Long lease times can also help.
  • Spanning tree learning mode blocks DHCP requests, which can significantly lengthen machine boot times, and even cause DHCP timeouts. Use portfast to turn off spanning tree on select ports. Good idea for workstation, too, by the way.
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