Netplan says "interface is not defined" when bridge uses "routes" instead of "gateway4"

[Brian Candler]

In netplan, gateway4 and gateway6 have been deprecated, and you're supposed to use "routes" instead. But this fails with a bridge interface.

===== Working configuration =====

network:
    bridges:
        br0:
            accept-ra: false
            addresses:
            - 100.64.0.250/22
            interfaces:
            - ens3
            nameservers:
                addresses:
                - 100.64.0.1
            parameters:
                forward-delay: 0
                stp: false
            gateway4: 100.64.0.1
    ethernets:
        ens3: {}
    version: 2

===== Broken configuration =====

network:
    bridges:
        br0:
            accept-ra: false
            addresses:
            - 100.64.0.250/22
            interfaces:
            - ens3
            nameservers:
                addresses:
                - 100.64.0.1
            parameters:
                forward-delay: 0
                stp: false
            routes:
            - to: 0/0
                via: 100.64.0.1
    ethernets:
        ens3: {}
    version: 2

The only difference is "gateway4" changed to "routes". With the second configuration, Netplan gives the following error:

root@noc:/etc/netplan# netplan generate
/etc/netplan/50-cloud-init.yaml:8:15: Error in network definition: br0: interface 'ens3' is not defined
            - ens3
              ^
root@noc:/etc/netplan#

As a result, the interface is not configured.

WORKAROUND: retain the deprecated gateway4: setting, as well as any additional routes you require. For example, the following is accepted (albeit with noisy deprecation warning):

            gateway4: 100.64.0.1
            routes:
            - to: 128.0.0.0/1
                via: 100.64.0.1

ProblemType: Bug
DistroRelease: Ubuntu 22.04
Package: netplan.io 0.105-0ubuntu2~22.04.1
ProcVersionSignature: Ubuntu 5.15.0-56.62-generic 5.15.64
Uname: Linux 5.15.0-56-generic x86_64
ApportVersion: 2.20.11-0ubuntu82.3
Architecture: amd64
CasperMD5CheckResult: unknown
Date: Thu Dec 22 15:50:59 2022
ProcEnviron:
 TERM=vt220
 PATH=(custom, no user)
 LANG=C.UTF-8
 SHELL=/bin/bash
SourcePackage: netplan.io
UpgradeStatus: No upgrade log present (probably fresh install)

[Danilo Egea Gondolfo (danilogondolfo)]

Thanks for your bug report.

Using 'to: 0/0' is not really supported by Netplan (although the documentation says it is). It was removed from the docs recently [1] but it wasn't updated yet.

Can you try using 'to: default' or 'to: 0.0.0.0/0' instead? It works for me.

Now, reporting that the ethernet interface is missing because of an invalid value in a non-related field is certainly not the desired behavior. I will look at it.

[1] https://github.com/canonical/netplan/commit/53e33fc716be10498f2fe789114e9339a38b281d

[Brian Candler (b-candler)]

Ha. Yes, with 0.0.0.0/0 it works. Thank you!

[Lukas Märdian (slyon)]

You could also be using "default" instead of "0.0.0.0/0".

Thanks for confirming this fixes the problem for you!

[Launchpad Janitor (janitor)]

This bug was fixed in the package netplan.io - 0.106-0ubuntu1

---------------
netplan.io (0.106-0ubuntu1) lunar; urgency=medium

  * New upstream release: 0.106
    - New 'netplan status' CLI (#290)
    - API: implement APIs from the new specification (#298)
    - Check and fix non-inclusive laguange (#303)
    - Documentation improvements (using Diátaxis & RTD)
    - Match by PermanentMACAddress (#278)
    - Netplan api iterator (#306)
    - API: update netplan_delete_connection() (#322)
    - NM 1.40 compat & file permission fixes (#300), LP: #1862600, LP: #1997348
    - Migrate from (deprecated) nose to pytest (#302)
    - parse: Add the filepath to OVS ports netdefs (#295)
    - Check if the interface name is too long (#313), LP: #1988749
    - doc/examples: remove unnecessary route for IPv6 on-link gateways (#312)
    - Memory leak CI action (#321)
    - tests:base:ethernets: Improve stability of autopkgtests (#223)
    Bug fixes:
    - Fix some memory leaks (#297)
    - parser: plug a memory leak (#309)
    - src:parse: plug memory leaks in nullable handling (#319)
    - Fix 'netplan ip leases' crash (#301), LP: #1996941
    - tests: mock calls to systemctl (#314)
    - ctests: fix an integer conversion issue (#315)
    - docs: small fix on netplan-set doc (#316)
    - parser: return the correct error on failure (#308), LP: #2000324
    - apply: Fix crash when OVS is stopped (#307),LP: #1995598
    - networkd: make sure VXLAN is in the right section (#310), LP: #2000713
    - cli:set: update only specific origin-hint if given (#299), LP: #1997467
    - vxlan: convert some settings to tristate (#311), LP: #2000712
    - parser: check for route duplicates (#320), LP: #2003061
  * Update symbols file for 0.106
  * d/patches/: Drop patches, applied upstream
  * d/control: bump Standards-Version to 4.6.2, no changes needed
  * d/t/control: prepare Debian testbed
  * d/control: Add python3-dbus, python3-rich deps, also CMocka and Pytest B-Ds
  * d/watch: fix checking for upstream tags
  * d/copyright: update for 2023
  * d/source/: add lintian-overrides

 -- Lukas Märdian <email address hidden> Thu, 09 Feb 2023 12:10:19 +0100