support firewall mark (fwmark) based routing for resolvers

[emlimap]

So in a multi wan setup, it would be good to route certain resolvers one path and others in another. At the moment, the way this can be done is by running one or more socks5 proxy server that can bind to specific wan interfaces.

While this works, this is less efficient considering the socks5 overhead. Instead, it would be far more efficient to mark the outgoing packets with a certain mark and IPtables & IP route will take care of routing it across the correct interface.

At the moment I use sing-box with routing mark (https://sing-box.sagernet.org/configuration/shared/dial/#routing_mark) which listens as socks5 proxy and it would be good to remove it from the loop. It is also written in Go so may provide you with some pointers if needed https://github.com/SagerNet/sing-box

[folbricht]

While that seems possible, there are some downsides. It's very low-level and requires making a few syscalls directly, and it'd be Linux-only as well.

Before going down that rabbithole, have you tried tagging the traffic with iptables and then route based on that tag. It should be straightforward to identify the traffic from routedns by destination+port, and I believe you could even tag all traffic emitted by the process.