DNS Search List

Glenn Satchell glenn.satchell at uniq.com.au
Sat Mar 20 13:53:32 UTC 2010

Hi Matt

You probably want option domain-search, which came out around 3.1.0. 
This is from the dhcp-options man page:

      option domain-search domain-list;

        The domain-search option  specifies  a  'search  list'  of
        Domain  Names  to  be  used  by  the client to locate not-
        fully-qualified domain names.  The difference between this
        option  and historic use of the domain-name option for the
        same ends is  that  this  option  is  encoded  in  RFC1035
        compressed labels on the wire.  For example:

          option domain-search "example.com", "sales.example.com",

You can set this within the subnet scope on your dhcp server. Assuming 
that each subnet is only located in one site, then you can reorder the 
search list for each subnet.


On 03/20/10 17:20, Matt Causey wrote:
> I am sure this has been discussed, but I sure can't find any reference
> to it...so I'll ask (again, most likely...).  :-)
> There doesn't appear to be a good way to specify a DNS search list in
> ISC dhcpd (or other implementations I've seen, for that matter).
> There is 'domain-name' - which is great, as long as you just need the
> one domain.  There are probably lots of good reasons that this is the
> case.  But what if I had multiple domains I wanted in the client's
> search list dynamically?
> Our clients are a mix of Windows and PXE booted linux clients.  The
> linux ones are udhcpd (busybox), ISC dhcpcd, and of course the lame
> dhcp client that comes on the boot ROM.  The server is linux ISC.
> We can solve it easily for the windows clients, that's just a group
> policy thing, or some kind of registry hack.
> But what about the linux clients?  Is there a way to tell the ISC dhcp
> client to accept the domain-name from the server, AND source a locally
> known list?
> For example...I have company.com.  I have site.company.com for each
> remote site.   In today's config, clients get a domain option of
> 'site.company.com'...which obviously corresponds to the site they are
> in.
> What I would like, is for clients to have a search list like this:
> company.com<-----hard-coded on the ISC dhcp client somehow
> site.company.com<---handed out via dhcpd
> Can the ISC dhcp client be configured to do this?  What are your thoughts?
> Thanks,
> --
> Matt

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