[Dnsmasq-discuss] Getting dnsmasq to serve fqdns as the hostname

Alex Kiernan alex.kiernan at gmail.com
Fri Oct 17 16:43:00 BST 2008

On Wed, Oct 15, 2008 at 9:38 PM, Simon Kelley <simon at thekelleys.org.uk> wrote:
> Alex Kiernan wrote:
>> On Tue, Oct 14, 2008 at 3:07 PM, Simon Kelley <simon at thekelleys.org.uk>
>> wrote:
>>> Alex Kiernan wrote:
>>>> On Tue, Oct 14, 2008 at 1:58 PM, Simon Kelley <simon at thekelleys.org.uk>
>>>> wrote:
>>>>> Alex Kiernan wrote:
>>>>>> I'm trying to use dnsmasq to serve DHCP/DNS for a Solaris network
>>>>>> install server (jumpstart). It works perfectly and the DNS/DHCP
>>>>>> integration means that lots of the traditional problems go away (the
>>>>>> problem is that the Solaris installation procedure won't setup DNS as
>>>>>> the name service unless you already have DNS for the machine you're
>>>>>> building in place).
>>>>>> dnsmasq works absolutely perfectly for this, with one minor problem -
>>>>>> I need to serve an FQDN in the hostname option; if I feed this to
>>>>>> dnsmasq in a dhcp-host then unless my domain setting matches it
>>>>>> rejects it, and even then it strips it to the basename. If instead I
>>>>>> force through an option 12, whilst it serves the FQDN, it doesn't
>>>>>> update the DNS so the DNS checks fail later in the install.
>>>>>> At the moment I'm working around it by removing the section of code
>>>>>> from check_dhcp_hosts which enforces the domain/fqdn
>>>>>> matching/stripping behaviour, but is there another way? Or another way
>>>>>> which I could implement which is cleaner?
>>>>> If you explicitly send the FQDN as option 12, set the basename (using
>>>>> dhcp-host) _and_ set the domain in dnsmasq to the correct value, I
>>>>> think
>>>>> that will do what you want assuming I've understood correctly that you
>>>>> want
>>>>> to
>>>>> 1) Send the FQDN as option 12
>>>>> 2) have the FQDN resolve in DNS to the IP address allocated.
>>>> Yeah, I should have mentioned that combo - it does exactly what I
>>>> need, but only for one domain, whereas I need it to work for many
>>>> domains (as I want this box to act as a jumpstart server across many
>>>> different hosts). If domain could be scoped with a tag that'd do what
>>>> I need (or even just support multiple maybe?)
>>> That (domain scoped with a tag) is a long-standing feature request which
>>> is
>>> impossible to do in a backwards compatible way. See this list passim for
>>> the
>>> gory details.
>>> HOWEVER, the next best thing (domain based on subnet or IP address range)
>>> is
>>> available at the bleeding edge. Try
>>> http://thekelleys.org.uk/dnsmasq/test-releases/dnsmasq-2.46test15.tar.gz
>> Thanks - I've had a play and it doesn't really do what I want as
>> whilst I have some networks which have one domain on a subnet, we have
>> others where we end up with a bunch of machines in differing domains.
>> Is there a good way to go about adding FQDN hostname functionality[1]?
>> If I could just add that one feature it'd do exactly what I need (when
>> coupled with the dhcp-fqdn option).
>> [1] which I'm happy to do and send you the diffs.
> The problem is that the format of the leases file is fixed to contain a
> non-fully qualified domain, and no domain field. To work, dnsmasq has to be
> able to determine the FQDN of a host using just the information in the
> leases file. Hence the new arrangement, which allows the domain to be
> derived from the IP address.
> To allow arbitrary domains means breaking the lease file format, which I
> don't want to do.
> Presumably, you add some configuration for each new host that you install,
> if that consists of something like
> dhcp-host=<mac address>,<IP address>,<bare name>,net:<FQDN>
> dhcp-option=net:<FQDN>,12,<FQDN>
> domain=<domain-fromFQDN>,<IP>,<IP>

Pretty much - a complete (Sparc) example is this:


> then that should work, domains don't have to be over whole subnets, just
> defined by IP address.

I was trying to avoid having to do static IP configuration at build as
even though that's the final config I need for most boxes, there are
some places where we have jumpstart servers on workstation networks
which are largely DHCP based; but thinking about it, on those networks
I'm constrained to using ISC DHCP anyway.

So next question... is adding support for dhcp-bootfile (to supply
multiple dhcp-boot options) and domain-file (to supply multiple domain
entries) as easy as it looks it ought to be? I'm happy to hack it in,
just wanted to make sure I wasn't opening a can of worms first!

Sorry, one last question - is there a way to stop dnsmasq sending a
router option for a network?

Alex Kiernan

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