Distributing DNS load via DHCP

Randall C Grimshaw rgrimsha at syr.edu
Fri Dec 16 16:57:04 UTC 2011

we built this logic into our scripts that produce and distribute updated dhcp configurations, thus the 'balancing' is more controlled by subnet assignment.

Randall Grimshaw rgrimsha at syr.edu
From: dhcp-users-bounces+rgrimsha=syr.edu at lists.isc.org [dhcp-users-bounces+rgrimsha=syr.edu at lists.isc.org] on behalf of Jeff Wieland [wieland at purdue.edu]
Sent: Friday, December 16, 2011 9:55 AM
To: Users of ISC DHCP
Subject: Distributing DNS load via DHCP

We have a fairly large pool of address, and we'd like to distribute
the DNS load on this pool between two DNS servers.

Roughly, what I was thinking of doing is:

group {
    default-lease-time 21600;
    max-lease-time 28800;
    option domain-name "myuni.edu";
    option domain-name-servers,;

    subnet netmask {
        option routers;
        # Select the DNS server order by examining the last bit of
        # the hardware address
        if (suffix(binary-to-ascii(2, 8, ":", hardware), 1) = "1") {
            option domain-name-servers,;
        } else {
            option domain-name-servers,;

        pool {
            deny dynamic bootp clients;

Or would I be better off doing something with classes/subclasses?
I'm concerned about the performance impact of the if statement.

          Jeff Wieland            |         Purdue University
   Network Systems Administrator  |        ITN&S Data Networks
       Voice: (765)496-8234       |        155 S. Grant Street
        FAX: (765)494-6620        |   West Lafayette, IN 47907-2115

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