[Dnsmasq-discuss] using dnsmasq for dns/dhcp with minimal dynamic changes to dns

Ben Cohen ncohen at ucsd.edu
Sat Jun 8 13:52:29 BST 2013


On Jun 8, 2013, at 6:59 PM, Ben Cohen <ncohen at ucsd.edu> wrote:

> Hi sorry to dredge up a question from the archives -- but this got put on hold and I'm just now implementing it.
> 
> I'm trying to ensure that dns always has forward and reverse entries for my hosts with static ip mappings.  Here's the question I asked and the response:
> 
> On Mar 1, 2013, at 10:38 PM, Simon Kelley <simon at thekelleys.org.uk> wrote:
> 
>> On 01/03/13 04:04, Nathaniel Cohen wrote:
>>> Hi -- I'm new to dnsmasq.  I've read through the docs but not yet
>>> configured the service for my environment.  I'll be using dnsmasq to
>>> manage dhcp and dns for a small network.
>>> 
>>> I've got a simple question but wasn't able to figure out the answer
>>> from the docs.  I need all the locally managed dns names under the
>>> purview of dnsmasq to be resolvable at all times -- regardless of the
>>> state of the client dhcp transactions/nic.  Is there a good pattern
>>> to do this without having to duplicate the host <-> ip address
>>> mapping information in more than one place …?
>>> 
>>> eg: If I use a set of entries like this:
>>> 
>>> dhcp-host=xx:xx:xx:xx:xx:xx, somedns, 10.10.1.1,  12h
>>> 
>>> Will somedns always resolve to 10.10.1.1 (and the reverse resolution
>>> from 10.10.1.1 to somedns) even if the dhcp client with that mac
>>> address is offline and/or has never performed a dhcp request …?
>> 
>> No the DNS records will only exist whilst a valid DHCP lease exists. You can do what you want but you need to split the configuration into two, though you don't need to duplicate the mappings.
>> 
>> The dnsmasq.conf configuration becomes.
>> 
>> dhcp-host=xx:xx:xx:xx:xx:xx, somedns, 12h
>> 
>> 
>> and then in /etc/hosts
>> 
>> 10.10.1.1   somedns
>> 
>> The /etc/hosts line will give you a permanent DNS entry, and the name will be looked up in the DNS which the DHCP lease is created and the address used for DHCP too.
>> 
>> 
>> If you want to keep everything in one file, you can use
>> 
>> host-record=somedns, 10.10.1.1
>> 
>> in dnsmasq.conf
>> 
>> instead of /etc/hosts.
> 
> I want to use the host-record= mechanism you describe.  Here's an example from my configuration:
> 
> dhcp-host=00:15:62:ff:b4:6e, set:is_wap4410n, set:adm, wap4410n-crstateroom, 12h
> host-record=wap4410n, 172.19.149.130

Typo in my first message (which is not a typo in the config file) -- same bug either way.  Starting dnsmasq never returns ...

dhcp-host=00:15:62:ff:b4:6e, set:is_wap4410n, set:adm, wap4410n-crstateroom, 12h
host-record=wap4410n-crstateroom, 172.19.149.130




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