This happens because the bridge interface comes up with carrier (specifically, with +LOWER_UP interface flag) and begins setting its addresses/routes, but then briefly loses carrier. I'm not sure why the bridge comes up with +LOWER_UP when ens3 appears to *not* be up:
Apr 27 10:46:56 lp1860926-f systemd-networkd[643]: br0: Flags change: +UP +LOWER_UP +RUNNING Apr 27 10:46:56 lp1860926-f systemd-networkd[643]: br0: Link UP Apr 27 10:46:56 lp1860926-f systemd-networkd[643]: br0: Gained carrier Apr 27 10:46:56 lp1860926-f systemd-networkd[643]: br0: Setting addresses ... Apr 27 10:46:56 lp1860926-f systemd-networkd[643]: br0: Remembering updated address: 192.168.122.105/24 (valid forever) ... Apr 27 10:46:56 lp1860926-f systemd-networkd[643]: br0: Flags change: -LOWER_UP Apr 27 10:46:56 lp1860926-f systemd-networkd[643]: br0: Lost carrier Apr 27 10:46:56 lp1860926-f systemd-networkd[643]: br0: Removing address 192.168.122.105 Apr 27 10:46:56 lp1860926-f systemd-networkd[643]: br0: State is configuring, dropping config Apr 27 10:46:56 lp1860926-f systemd-networkd[643]: ens3: Joined netdev Apr 27 10:46:56 lp1860926-f systemd-networkd[643]: ens3: Bringing link up Apr 27 10:46:56 lp1860926-f systemd-networkd[643]: br0: Flags change: -RUNNING Apr 27 10:46:56 lp1860926-f systemd-networkd[643]: br0: Remembering updated address: 192.168.122.105/24 (valid forever) Apr 27 10:46:56 lp1860926-f systemd-networkd[643]: br0: Addresses set Apr 27 10:46:56 lp1860926-f systemd-networkd[643]: br0: Configuring route: dst: n/a, src: n/a, gw: 192.168.122.1, prefsrc: n/a, scope: global, table: main, proto: static, type: unicast Apr 27 10:46:56 lp1860926-f systemd-networkd[643]: br0: Setting routes Apr 27 10:46:56 lp1860926-f systemd-networkd[643]: br0: Forgetting address: 192.168.122.105/24 (valid forever) ... Apr 27 10:46:56 lp1860926-f systemd-networkd[643]: ens3: Flags change: +UP +LOWER_UP +RUNNING Apr 27 10:46:56 lp1860926-f systemd-networkd[643]: ens3: Link UP ... Apr 27 10:46:56 lp1860926-f systemd-networkd[643]: ens3: Gained carrier ... Apr 27 10:46:56 lp1860926-f systemd-networkd[643]: br0: Flags change: +LOWER_UP +RUNNING Apr 27 10:46:56 lp1860926-f systemd-networkd[643]: br0: Gained carrier Apr 27 10:46:56 lp1860926-f systemd-networkd[643]: br0: Setting addresses Apr 27 10:46:56 lp1860926-f systemd-networkd[643]: br0: Could not set route: Nexthop has invalid gateway. Network is unreachable Apr 27 10:46:56 lp1860926-f systemd-networkd[643]: br0: Failed ... Apr 27 10:46:56 lp1860926-f systemd-networkd[643]: br0: Remembering updated address: 192.168.122.105/24 (valid forever) Note that on carrier loss, networkd begins removing the address, but doesn't actually complete address removal until after carrier is back up, which then causes setting the network route to fail, right before the address is added again. With upstream systemd, this doesn't happen, because the bridge interface comes up without carrier (again, specifically, without +LOWER_UP interface flag): Apr 27 10:23:05 lp1860926-u systemd-networkd[600]: br0: Flags change: +UP Apr 27 10:23:05 lp1860926-u systemd-networkd[600]: br0: Link UP Apr 27 10:23:05 lp1860926-u systemd-networkd[600]: br0: Remembering updated address: 192.168.122.231/24 (valid forever) ... Apr 27 10:23:05 lp1860926-u systemd-networkd[600]: br0: Addresses set Apr 27 10:23:05 lp1860926-u systemd-networkd[600]: br0: Configuring route: dst: n/a, src: n/a, gw: 192.168.122.1, prefsrc: n/a, scope: global, table: main, proto: static, type: unicast Apr 27 10:23:05 lp1860926-u systemd-networkd[600]: br0: Setting routes ... Apr 27 10:23:05 lp1860926-u systemd-networkd[600]: ens3: Joined netdev Apr 27 10:23:05 lp1860926-u systemd-networkd[600]: ens3: Bringing link up Apr 27 10:23:05 lp1860926-u systemd-networkd[600]: br0: Received remembered route: dst: n/a, src: n/a, gw: 192.168.122.1, prefsrc: n/a, scope: global, table: main, proto: static, type: unicast Apr 27 10:23:05 lp1860926-u systemd-networkd[600]: br0: Routes set Apr 27 10:23:05 lp1860926-u systemd-networkd[600]: br0: State changed: configuring -> configured Apr 27 10:23:05 lp1860926-u systemd-networkd[600]: ens3: Flags change: +UP +LOWER_UP +RUNNING Apr 27 10:23:05 lp1860926-u systemd-networkd[600]: ens3: Link UP ... Apr 27 10:23:05 lp1860926-u systemd-networkd[600]: ens3: Gained carrier Apr 27 10:23:05 lp1860926-u systemd-networkd[600]: ens3: State changed: configuring -> configured ... Apr 27 10:23:05 lp1860926-u systemd-networkd[600]: br0: Flags change: +LOWER_UP +RUNNING Apr 27 10:23:05 lp1860926-u systemd-networkd[600]: br0: Gained carrier Apr 27 10:23:05 lp1860926-u systemd-networkd[600]: br0: State changed: configured -> configuring Apr 27 10:23:05 lp1860926-u systemd-networkd[600]: br0: Setting addresses ... Apr 27 10:23:05 lp1860926-u systemd-networkd[600]: br0: Remembering updated address: 192.168.122.231/24 (valid forever) Apr 27 10:23:05 lp1860926-u systemd-networkd[600]: br0: Addresses set Apr 27 10:23:05 lp1860926-u systemd-networkd[600]: br0: Configuring route: dst: n/a, src: n/a, gw: 192.168.122.1, prefsrc: n/a, scope: global, table: main, proto: static, type: unicast Apr 27 10:23:05 lp1860926-u systemd-networkd[600]: br0: Setting routes Apr 27 10:23:05 lp1860926-u systemd-networkd[600]: br0: Routes set Note in both situations, the bridge interface happens twice. This is because netplan adds ConfigureWithoutCarrier=yes to the bridge configuration, which causes networkd to start configuring the bridge before it's ready. However, netplan doesn't also set IgnoreCarrierLoss=yes, so networkd removes the bridge configuration when it detects carrier loss, which results in a race condition to re-setup the bridge when the carrier is lost, since the loss happens in the middle of initial configuration. If the networkd configuration is changed to remove ConfigureWithoutCarrier=yes (or set it to no/false), or if the networkd configuration is changed to add IgnoreCarrierLoss=yes (and leave ConfigureWithoutCarrier=yes), then this bug *appears* fixed, at least in my testing. However, I'm still concerned about this race and I haven't had time to fully analyze the situation of carrier drop during configuration; I feel like this is still a potential issue regardless of the ConfigureWithoutCarrier and/or IgnoreCarrierLoss settings. For now, I'll build a test kernel that defaults IgnoreCarrierLoss= to the value of ConfigureWithoutCarrier= (and open an upstream bug) to see if that also fixes this for others affected. -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1860926 Title: Ubuntu 20.04 Systemd fails to configure bridged network To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/systemd/+bug/1860926/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
