Bug#805344: systemd: ListenStream=6566 in saned.socket only causes systemd to listen on [::]:6566

[Ansgar Burchardt]

Jens Georg <jens.georg at jensge.org> writes:
> I was trying to run sane network scanning through socket activation, but
> with the provided saned.socket file systemd only listens on a v6 socket.
> I have to explicitly change ListenStream to 0.0.0.0:6656 to make it
> listen on v4.

Did you check if it is actually not reachable over IPv4? IPv6 sockets
can also accept IPv4 connections unless configured not to do so. This is
controlled system-wide via /proc/sys/net/ipv6/bindv6only which is "0" on
my computer (which is the default according to man:systemd.socket(5)).

systemd by default binds only to IPv6, but uses the system-wide default
above to also accept IPv4 connections; the default can also be
overridden per-service via BindIPv6Only= (see man:systemd.socket(5)).

Ansgar