Bug#1063995: networkd: route with PreferredSource not created

[Sven Feyerabend]

Package: systemd
Version: 252.22-1~deb12u1
Severity: normal
X-Debbugs-Cc: Sven.Feyerabend at stuvus.uni-stuttgart.de

Dear Maintainer,

we've been using a wireguard setup to connect hosts.
After upgrading to Debian 12 (systemd 247 to systemd 252) the default
route, which has a PreferredSource set is no longer created.

To reproduce the issue, consider the following setup:
* Interface 1: physical interface, configured for DHCP, routes are added to table 2:
[Match]
Name=eno1

[Network]
DHCP=ipv4
IPForward=True
DNS=XXX.XXX.XXX.XXX
KeepConfiguration=dhcp

[DHCPv4]
UseDNS=False
RouteTable=2

* Interface 2: the wireguard interface:
[Match]
Name=wg_rtr

[Address]
Address=10.53.16.8/32
Peer=192.168.30.1/32

[Address]
Address=fe80::1/64

[Link]
MTUBytes=1500

[Route]
Destination=0.0.0.0/0
Gateway=192.168.30.1
PreferredSource=10.53.16.8

[RoutingPolicyRule]
Priority=1
IncomingInterface=lo
IPProtocol=udp
DestinationPort=51848
Table=2

With this setup, the default route is not created at all and the default
routing table looks like this:
$ ip r s
192.168.30.1 dev wg_rtr_nili01 proto kernel scope link src 10.53.16.8 

On Debian 11 (systemd 247.3-7+deb11u4) this exact same config produces
the correct default route:
$ ip r s
default via 192.168.30.1 dev wg_rtr proto static src 10.53.16.8 
192.168.30.1 dev wg_rtr proto kernel scope link src 10.53.16.8 


If I omit the PreferredSource option from the [Route] section,
everything works as expected:
$ ip r s
default via 192.168.30.1 dev wg_rtr proto static 
192.168.30.1 dev wg_rtr proto kernel scope link src 10.53.16.8 

Kind regards,
Sven

-- Package-specific info:

-- System Information:
Debian Release: 12.5
  APT prefers stable-updates
  APT policy: (500, 'stable-updates'), (500, 'stable-security'), (500, 'stable')
Architecture: amd64 (x86_64)

Kernel: Linux 6.1.0-13-amd64 (SMP w/4 CPU threads; PREEMPT)
Locale: LANG=en_US.UTF-8, LC_CTYPE=en_US.UTF-8 (charmap=UTF-8), LANGUAGE=en_US:en
Shell: /bin/sh linked to /usr/bin/dash
Init: systemd (via /run/systemd/system)
LSM: AppArmor: enabled

Versions of packages systemd depends on:
ii  libacl1            2.3.1-3
ii  libaudit1          1:3.0.9-1
ii  libblkid1          2.38.1-5+b1
ii  libc6              2.36-9+deb12u4
ii  libcap2            1:2.66-4
ii  libcryptsetup12    2:2.6.1-4~deb12u2
ii  libfdisk1          2.38.1-5+b1
ii  libgcrypt20        1.10.1-3
ii  libkmod2           30+20221128-1
ii  liblz4-1           1.9.4-1
ii  liblzma5           5.4.1-0.2
ii  libmount1          2.38.1-5+b1
ii  libp11-kit0        0.24.1-2
ii  libseccomp2        2.5.4-1+b3
ii  libselinux1        3.4-1+b6
ii  libssl3            3.0.11-1~deb12u2
ii  libsystemd-shared  252.22-1~deb12u1
ii  libsystemd0        252.22-1~deb12u1
ii  libzstd1           1.5.4+dfsg2-5
ii  mount              2.38.1-5+b1

Versions of packages systemd recommends:
ii  dbus [default-dbus-system-bus]   1.14.10-1~deb12u1
ii  systemd-timesyncd [time-daemon]  252.22-1~deb12u1

Versions of packages systemd suggests:
ii  libfido2-1            1.12.0-2+b1
pn  libqrencode4          <none>
pn  libtss2-esys-3.0.2-0  <none>
pn  libtss2-mu0           <none>
pn  libtss2-rc0           <none>
ii  policykit-1           122-3
ii  polkitd               122-3
pn  systemd-boot          <none>
ii  systemd-container     252.22-1~deb12u1
pn  systemd-homed         <none>
ii  systemd-resolved      252.22-1~deb12u1
pn  systemd-userdbd       <none>

Versions of packages systemd is related to:
ii  dbus-user-session  1.14.10-1~deb12u1
pn  dracut             <none>
ii  initramfs-tools    0.142
ii  libnss-systemd     252.22-1~deb12u1
ii  libpam-systemd     252.22-1~deb12u1
ii  udev               252.22-1~deb12u1

-- Configuration Files:
/etc/systemd/journald.conf changed [not included]

-- no debconf information