Dual DNS server farms in dhcpd.conf

Simon Hobson dhcp1 at thehobsons.co.uk
Tue Apr 28 08:43:06 UTC 2009


John Tabasz (jtabasz) wrote:

>I have a situation where I want to use dhcpd.conf to serve up addresses
>that are statically assigned. I have previously used the following to do
>this:
>
>shared-network TEST  {
>
>subnet 192.168.200.0 netmask 255.255.255.0 {
>option routers 192.168.200.1;
>   option subnet-mask 255.255.255.0;
>   option domain-name-servers 10.1.1.25,10.1.2.25,10.1.3.25;
>   option domain-name "mydomain.com";
>deny unknown-clients;
>}
>
>   host dev5c.mydomain.com                           {
>    hardware ethernet              0:3:ba:11:b1:75;
>    fixed-address                   192.168.200.165;
>    option host-name                       "dev5c";
>   }
>
>}
>
>This worked fine until a new requirement came up that the PCs on the
>network and the Unix workstations on the same subnet should receive a
>different set of DNS server IP addresses.

First off, ditch the shared-network, it's only going to confuse 
things. Putting the host statements inside a scope other than global 
isn't generally a good idea - some stuff is inherited from where they 
are defined, but the host declaration is globally valid, the result 
being that a host can get some options from one subnet, and others 
from another.

Also, is there only one subnet ? It makes a big difference to options 
available to you.


One option would be to simply add a dns server option to the host 
declarations for the Unix boxes. Eg :

   host x.mydomain.com                           {
    hardware ethernet              0:3:ba:11:b1:75;
    fixed-address                   192.168.200.165;
    option host-name                       "x";
    option domain-name-servers a.b.c.d;
   }

Rather than add this to each host declaration, you can put them in a 
group like this :

group
   option domain-name-servers a.b.c.d;
   host x.mydomain.com                           {
    hardware ethernet              0:3:ba:11:b1:75;
    fixed-address                   192.168.200.165;
    option host-name                       "x";
   }
   host y.mydomain.com                           {
    hardware ethernet              0:3:ba:11:b1:76;
    fixed-address                   192.168.200.166;
    option host-name                       "y";
   }
}


-- 
Simon Hobson

Visit http://www.magpiesnestpublishing.co.uk/ for books by acclaimed
author Gladys Hobson. Novels - poetry - short stories - ideal as
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