[Dnsmasq-discuss] dnsmasq responding to DHCPINFORM only

[Simon Kelley]

On 29/12/11 16:30, Nabeel Jafferali wrote:
> Hello.
> 
> We've recently noticed a problem with our setup, that was based on the
> information in this (old) thread.
> 
> Essentially, we used Simon's instructions (below) to configure dnsmasq to
> not reply to DHCP requests for leases, but to only respond to DHCP INFORM
> requests. We also had option 66 parameters configued for a specific MAC
> address range. This worked great in our scenario, where we had devices
> getting IP/DNS/etc. from the primary DHCP server, and subsequently getting
> DHCP option 66 info from the dnsmasq instance replying to a DHCP INFORM
> request.
> 
> However, we've noticed some Windows PCs also request DHCP INFORM, and it
> appears dnsmasq replies to those requests and provides DNS server
> information - those PCs then start to use the DNS servers supplied by
> dnsmasq instead of the DNS servers supplied by the primary DHCP server.
> 
> A few questions:
> 
> 1. How can I cause dnsmasq to only reply to DHCP INFORM requests from a
> certain MAC range? I already have the MAC range configured, and have
> dnsmasq configured to provide specific option 66 information to that MAC
> range only.

dhcp-ignore = !<tag> will stop all replies except when the tag is set.
Use the same tag you set on the MAC range, and it will work fine.

> 2. If not possible, how can I cause DNS server information to not be
> included in the reply to DHCP INFORM?

dhcp-option = option:dns-server

(Dnsmasq uses itself as the default DNS server, the above overrides the
default and sets no DNS server option.

> 3. If both not possible, where do I specify the specific DNS servers which
> dnsmasq uses in the aforementioned reply? Perhaps I can just replicate the
> information that the primary DHCP server sends.
> 

Some variation on the example above will work for this.

HTH

Simon.

>