[Dnsmasq-discuss] Telling dnsmasq *not* to send router option??

[Rance Hall]

On Thu, Aug 2, 2012 at 12:49 PM, John Hallam <dns at j.hallam.dk> wrote:
> I have a situation where my laptop sometimes connects to my IPv4 home
> network over VPN and sometimes directly.  I want to use DHCP to
> allocate the address of the VPN endpoint on the laptop, to be the same
> as when it is connected directly to my wired network.  This basically
> works fine.
>
> However, the DHCP client wants to set up a default route, but does it
> wrong.  OpenVPN knows how to do this right, and has already set the
> default routing configuration correctly to point to the VPN tunnel,
> except for those cases that should not route that way, so I want the
> DHCP client not to set the default route.
>
> Is it possible to instruct dnsmasq to refuse to send dhcp option 3
> (router) and would this inhibit the DHCP client from setting a default
> route?
>
> (There are various reasons why I can't change the DHCP client and why
> this behaviour needs to be server-driven.)
>
> Any suggestions received gratefully...
>
> Thanks,
>
>         John Hallam


John:

I have had limited success in scenarios like the one you describe.
Every time I configure dnsmasq to not send a dhcp option I end up
breaking something else I was not planning on.

Some other device needed the option and is now broken because the
option does not exist.

Some dhcp clients have a strange way of inventing values they need if
they think they need them and the answers are not provided,  in some
cases even the IP address itself.

I have always been eventually forced to alter the dhcp client in some way.

FWIW, I have used OpenVPN and Dnsmasq together and been very happy
with the setup but I don't have a working setup available to me at the
moment so I can't look up any configuration details.