openresolv-discuss

Hi

On 14/08/2012 23:06, Ed W wrote:
> Hi, DNSMasq has an option to restrict the use of a DNS server to a
> specific interface. (format is server=1.2.3.4@eth1 )

No, it means that queries to that DNS server 1.2.3.4 will be sent via 
eth1.
AFAIK it has no relevance in DNSmasq selecting which DNS server to 
actually query.

> For several situations I would like to limit my DNS as far as
> possible to specific upstream servers, however, in the case of 
> captive
> portals and wifi access it's often necessary to compromise and allow
> some new DNS server to be used since others might be blocked.  I 
> would
> like to avoid "tainting" traffic by avoiding that DNS server where I
> can
>
> Ideally this is a feature request that dhcpcd can be set to restrict
> dns to just that interface and in turn it indicates this to
> openresolv, which in turn would only support this on the subset of
> resolvers which can limit requests by interface
>
> I'm not actually sure that this isn't a very common use case for the
> situation of having a globally accessible DNS
> (OpenDNS/GoogleDNS/Something Else), but various interfaces are trying
> to add additional DNS servers.  Eg adding my 3G data card as an
> available backup route is currently adding those DNS entries even
> though I might be using a DSL line at present.  DNSmasq is smart
> enough to latch on to the "fastest responding server", but in the
> event that not all DNS servers are the same, then I would prefer to
> lock the 3G DNS server to only be available over that 3G connection.
>
> Would you consider such a feature request? Is there some existing
> ability that I might have overlooked that can implement this?

I'm not entirely sure what you're asking for.
An application generally tells the host "I want to look up domain foo".
At no point in this request is an interface specificed - it's interface 
agnostic.

However, it's possible for openresolv to configure DNSmasq (unbound, 
bind) to only send queries for domain foo to 1.2.3.4.
But I'm not sure this is what you want either.

What openresolv can do is prefer each interface by metric as such and 
force an ordering on the DNS servers listed.
Generally DNS resolvers try the forwarders in order first and you can 
force DNSmasq to do this by using the strict-order option.
Doing this, your 3G DNS servers will be last in the food chain and only 
used if all else fails.

Thanks

Roy