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

Todd Sankey dev at lutean.com
Wed Apr 19 19:36:46 BST 2017

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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