[PVE-User] OSPF when migrating from v8 to v9

[Stefan Hanreich]

On 10/8/25 12:47 PM, Julien OHAYON wrote:
> My concern is during the migration: if I configure OSPF on a node running v9, will this have an impact on the nodes still running v8?

This one is a bit tricky to answer because of a change in the reload
endpoint between 8 and 9. The behavior depends on certain factors (which
node initiates the reload, how your SDN configuration looks like, ...).

This is due to the introduction of an additional API parameter that is
incompatible with PVE 8.x instances. For that reason, we recommend only
mixing major versions in a cluster while performing an upgrade, not for
prolonged periods of time. We do *not* recommend doing any configuration
changes while your cluster is on mixed major versions. Problems like
this can occur due to changes between major versions and we cannot
guarantee correct behavior while your cluster is running on mixed major
versions.


That being said, upgrading from 8 to 9 alone should not cause your
custom /etc/frr/daemons file to get overwritten - since the SDN stack
only writes to it when re-generating the configuration (= applying the
SDN configuration).

If you upgrade from an earlier FRR version (8), then you would get a
prompt that the daemons file changed, asking you to review you the
changes - like so:

Configuration file '/etc/frr/daemons'
 ==> Modified (by you or by a script) since installation.
 ==> Package distributor has shipped an updated version.
   What would you like to do about it ?  Your options are:
    Y or I  : install the package maintainer's version
    N or O  : keep your currently-installed version
      D     : show the differences between the versions
      Z     : start a shell to examine the situation
 The default action is to keep your current version.
*** daemons (Y/I/N/O/D/Z) [default=N] ?

Upgrading from 10.2 (with ospfd=yes) does not cause a prompt to appear
and the daemons file stays untouched.


I've also verified this right now by upgrading a PVE 8 instance with
ospfd=yes in its daemon file. Upgrading itself did not overwrite the
directive in the daemons file - only reapplying the SDN configuration
does set it to ospfd=no.

So, as long as you do not re-apply the SDN configuration in any way,
your OSPF directive in the daemons file stays untouched. On PVE9, when
applying a SDN configuration that contains either a fabric or an EVPN
controller will overwrite the FRR configuration (including the daemons
file).