pfSense

It uses the gateway specified on the selected interface, it's a way to associate DNS servers with a particular ISP.

It seems to me, it should be added in the remark to an option.

If you need to use something other than the primary gateway on the interface (which is rare), you can choose none and add a static route.

If to use rules pf it will be possible to specify group gateways for failover.

For example so:

pass out $GWFailover proto { tcp udp } from any to ##DNS_IP## port 53 keep state

yes that's all possible. You can do that manually as well, with floating rules. It's definitely something we should consider in the future. It's not a bug though, it works as intended.

Chris Buechler wrote:

yes that's all possible. You can do that manually as well, with floating rules.

I just gave it a try with floating rules, but tcpdump shows that still the default GW interface is being used for DNS resolution.

Chris, is there anything to be taken care of specifically in order to get this to work?

it's possible. That's a support request, which isn't appropriate here, please use one of our available support resources. https://pfsense.org/support