[Bug 1874515] Re: 20.04 does not bring up certain bridges

[Mikael]

Added the full syslog output covering the two boots aswell.

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Title:
  20.04 does not bring up certain bridges

Status in ifupdown package in Ubuntu:
  New

Bug description:
  After upgrading from a fully patched ubuntu-server 18.04 to 20.04 and
  rebooting I noticed that some of my bridge interfaces defined in
  /etc/network/interfaces would not come up while others would.

  Bridges brought up at boot:

  br_ext_prim
  br_ext_sec
  br_int_50
  br_nat

  Bridges missing:

  br_int_500
  br_nat_ext

  
  Relevant log from 18.04 prior to upgrade:

  Apr 23 19:11:37 fancy systemd-udevd[725]: Could not generate persistent MAC address for br_nat_ext: No such file or directory
  Apr 23 19:11:37 fancy systemd[1]: Found device /sys/subsystem/net/devices/br_nat_ext.
  Apr 23 19:11:37 fancy systemd[1]: Started ifup for br_nat_ext.
  Apr 23 19:11:37 fancy systemd-networkd[2284]: br_nat_ext: Link UP
  Apr 23 19:11:37 fancy sh[2383]: Waiting for br_nat_ext to get ready (MAXWAIT is 5 seconds).
  Apr 23 19:11:37 fancy kernel: [    9.447538] br_nat_ext: port 1(int0.51) entered blocking state
  Apr 23 19:11:37 fancy kernel: [    9.447540] br_nat_ext: port 1(int0.51) entered disabled state
  Apr 23 19:11:37 fancy systemd-networkd[2284]: br_nat_ext: Gained carrier
  Apr 23 19:11:37 fancy kernel: [   10.942682] br_nat_ext: port 1(int0.51) entered blocking state
  Apr 23 19:11:37 fancy kernel: [   10.942683] br_nat_ext: port 1(int0.51) entered forwarding state
  Apr 23 19:11:37 fancy kernel: [   10.943270] IPv6: ADDRCONF(NETDEV_CHANGE): br_nat_ext: link becomes ready
  Apr 23 19:11:39 fancy systemd-networkd[2284]: br_nat_ext: Gained IPv6LL

  
  Relevant log from 20.04 after upgrade:

  Apr 23 19:39:52 fancy ifup[1845]: br_nat_ext: ERROR while getting interface flags: No such device
  Apr 23 19:39:52 fancy ifup[1066]: ifup: failed to bring up br_nat_ext
  Apr 23 19:40:04 fancy libvirtd[1935]: Cannot get interface MTU on 'br_nat_ext': No such device
  Apr 23 19:40:04 fancy libvirtd[1935]: internal error: Failed to autostart VM 'dns': Cannot get interface MTU on 'br_nat_ext': No such device
  Apr 23 19:43:43 fancy libvirtd[1935]: Cannot get interface MTU on 'br_nat_ext': No such device
  Apr 23 19:39:52 fancy systemd[1]: networking.service: Main process exited, code=exited, status=1/FAILURE
  Apr 23 19:39:52 fancy systemd[1]: networking.service: Failed with result 'exit-code'.
  Apr 23 19:39:52 fancy systemd[1]: Failed to start Raise network interfaces.

  
  Similar logs show up for br_int_500.

  
  Some examples of entries of /etc/network/interfaces:

  Not working:

  # NAT via main FW
  auto int0.51
  iface int0.51 inet manual
         vlan-raw-device int0
         pre-up ifconfig $IFACE up
         post-down ifconfig $IFACE down

  auto br_nat_ext
  iface br_nat_ext inet manual
          bridge_ports int0.51
          bridge_maxwait 5
          pre-up ifconfig $IFACE up
          post-down ifconfig $IFACE down

  
  Working:

  # 1GE
  auto ext0.10
  iface ext0.10 inet manual
          vlan-raw-device ext0
          pre-up ifconfig $IFACE up
          post-down ifconfig $IFACE down

  # Secondary bridge 1GE
  auto br_ext_sec
  iface br_ext_sec inet manual
          bridge_ports ext0.10
          bridge_maxwait 5
          post-up ifconfig $IFACE up
          post-down ifconfig $IFACE down

  
  Output from syslog in regards to br_ext_sec after upgrade:

  Apr 23 19:39:52 fancy systemd-udevd[1366]: br_ext_sec: Could not generate persistent MAC: No data available
  Apr 23 19:39:52 fancy kernel: [   24.353151] br_ext_sec: port 1(ext0.10) entered blocking state
  Apr 23 19:39:52 fancy kernel: [   24.353156] br_ext_sec: port 1(ext0.10) entered disabled state
  Apr 23 19:39:52 fancy systemd-networkd[620]: br_ext_sec: Link UP
  Apr 23 19:39:52 fancy ifup[1538]: Waiting for br_ext_sec to get ready (MAXWAIT is 5 seconds).
  Apr 23 19:39:52 fancy kernel: [   24.360953] br_ext_sec: port 1(ext0.10) entered blocking state
  Apr 23 19:39:52 fancy kernel: [   24.360956] br_ext_sec: port 1(ext0.10) entered forwarding state
  Apr 23 19:39:52 fancy systemd[1]: Found device /sys/subsystem/net/devices/br_ext_sec.
  Apr 23 19:39:52 fancy systemd[1]: Started ifup for br_ext_sec.
  Apr 23 19:39:52 fancy sh[1547]: ifup: waiting for lock on /run/network/ifstate.br_ext_sec
  Apr 23 19:39:52 fancy sh[1547]: ifup: interface br_ext_sec already configured
  Apr 23 19:39:53 fancy systemd-networkd[620]: br_ext_sec: Gained carrier

  
  No changes applied to /etc/network/interfaces between boots. No complaints from upgrade process otherwise.

  Attaching a slightly redacted interfaces file from the system in the
  ticket aswell.

  Thanks :)

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