Unable to bind to 0.0.0.0:53 when systemd-resolved is running

[ghost]

This is the same issue as #680, just ran into it again on Ubuntu 18.04. Any example you have that tries to bind to port 53 while systemd-resolved should trigger this.

[ghost]

I think we need SO_REUSEADDR: https://stackoverflow.com/questions/14388706/socket-options-so-reuseaddr-and-so-reuseport-how-do-they-differ-do-they-mean-t

[ghost]

Related: #487

Would be nice to request socket options with this library.

[miekg]

[ Quoting <[email protected]> in "[miekg/dns] Unable to bind to 0.0.0..." ]

This is the same issue as #680, just ran into it again on Ubuntu 18.04. Any example you have that tries to bind to port 53 while systemd-resolved should trigger this.

you bind to a port where something is running... that's WAI

[ghost]

systemd-resolved is bound to 127.0.0.53 port 53 with SO_REUSEADDR. If we have the option to enable SO_REUSEADDR when binding 0.0.0.0 port 53, these two can coexist just fine.

[tmthrgd]

@teran-mckinney SO_REUSEADDR hasn’t been implemented, while SO_REUSEPORT has been. After some quick reading, what you’re trying to do is valid and exactly what SO_REUSEADDR was designed for. (This is a somewhat verbose explanation: https://stackoverflow.com/a/14388707).

It wouldn’t be a huge amount of work to add, but we would start to get a multitude of socket options hanging off Server.

[ghost]

Thanks for looking into this. I agree, maybe there's a cleaner way to implement the options but I don't know Go very well.

[miekg]

you should make your own conn and use that; not something this lib should provide.

[ghost]

you should make your own conn and use that; not something this lib should provide.

Could you provide an example on how to do that? I've looked through the examples in exdns and can't see any cases where you made the socket and put a DNS server on that socket.

[tmthrgd]

@teran-mckinney Use the ListenConfig type and it’s methods from the net package to create a connection with the SO_REUSEADDR flag set (see listen_go111.go). Then set either the Listener or PacketConn fields on Server and call ActivateAndServe like you would ListenAndServe.

[ghost]

@tmthrgd thank you! I appreciate it.