[Dnsmasq-discuss] Disabling dynamic DHCP assignment for known hosts

Simon Kelley simon at thekelleys.org.uk
Sun Apr 23 15:37:40 BST 2017

I like this. (Almost) completely backwards compatible, obvious to use,
solves a problem. What do people think?

I think the implementation is over-complex: calling find_config() with
the context set to NULL is all that's needed to implementthe search, but
that's a detail.



On 19/04/17 19:36, Todd Sankey wrote:
> I tried a different approach. I created a patch (attached) so that the tag
> "knownother" is applied if there is a host definition that applies to a
> different context. In our setup, we then added "dhcp-ignore=tag:knownother".
> On Wed, Mar 15, 2017 at 1:14 PM, Todd Sankey <dev at lutean.com> wrote:
>> Our setup has two wifi networks with different network addresses, one for
>> employees and one for guests. On the employee network, the hosts all have
>> static host entries that include IP addresses. The guest network has no
>> static host entries. What we would like to do is prevent the employee
>> machines from getting any assignment on the guest network.
>> We tried using "tag:!known" in the dhcp-range configuration, and we have
>> tried a tag-if statement that sets a tag based on the guest network
>> interface and known followed by a dhcp-ignore. Neither works.
>> Looking through the code, I think it is because when looking for a
>> dhcp_config entry, the search is filtered by whether the assigned address
>> is valid for the interface the request was received on. Since the static
>> assignments are only valid for the employee network, when a request is
>> received on the guest network, the static assignments are not valid so the
>> "known" tag is never set. As a result, neither the dhcp-range tag filter
>> nor the tag-if filter has the desired effect.
>> I next tried having dhcp-host entries for every employee machine, one with
>> a static assignment on the employee network, and one with a static
>> assignment on guest network and appending "ignore" to the guest network
>> entry. This seems to have the desired behaviour in that employee machines
>> cannot get on the guest network. However, this obviously doubles the work
>> of maintaining the host list. I am also not sure what this does to the
>> guest address range having these static but ignored assignments.
>> Is there a better way to do this in the current version (2.76)?
>> If not, would it be a reasonable feature request to extend the handling of
>> dhcp-host settings so that if there is an IP assignment and "ignore" is
>> specified, then the host is ignored on networks where the IP assignment is
>> not valid?
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