Bug#1125735: Consider changing the default RoutePriorityOffset (iwd) or DHCP_ROUTE_METRIC (systemd-networkd)

[Helmut Grohne]

Package: iwd,systemd
Severity: wishlist

Hello Jonas, Luca and other systemd maintainers,

I am using iwd (for wireless interfaces) and systemd-networkd (for wired
interfaces) and this mostly works like a charm. There is one aspect that
works less than ideal in the default configuration and it is route
metrics.

With networkd, a simple DHCP=yes .network file typically does the job
for ethernet interfaces and things just work once plugging a cable.
Likewise, iwd recognizes configured networks and connects to them
automatically. Both tend to install a default route and this is where it
gets interesting. The existence of multiple routes actually is
beneficial, because existing network connections don't have to die. When
establishing a new connection, Linux selects the preferred route via its
metric value. Both tools override Linux default. iwd defaults to
RoutePriorityOffset=300 and systemd-networkd #defines DHCP_ROUTE_METRIC
as 1024. When both interfaces are configured, wireless is preferred, but
that is rarely what we want as network cables typically offer higher
speed.

Changing this is easy enough. Setting a differen RoutePriorityOffset on
the iwd side is a one-line change as is setting RouteMetric in the
.network file.

I am wondering whether these defaults are useful or whether we may
consider changing them for a better default behavior. Of course changing
defaults bears downsides. Users may have come to rely on the current
defaults, so it would be a breaking change. Deviating from upstream on
the Debian side may cause surprises. So it's not obvious that a change
is beneficial from a global perspective. If both of you disagree with
changing them, please tag this bug wontfix and close it.

Helmut