ifupdown2 not backward-compatible with ifupdown

[jaqxues]

We recently tried upgrading a machine from PVE 6.x to PVE 7.x. The official instructions say that installing ifupdown2 and uninstalling ifupdown would work as replacement. We use ifupdown + resolvconf.

However, ifupdown and ifupdown2 behave differently with our /etc/networking/interfaces file. The symptom that we had was the DNS servers were not set during boot (or with ifreload -a etc).

The resolvconf (/etc/network/if-up.d/000resolvconf) hook is called by ifupdown twice, once for ipv4 and once for ipv6 configurations (so once with ADDRFAM=inet and once with ADDRFAM=inet6). However, the newer ifupdown2 calls the hook only once for the interface, with both at the same time (ADDFRAM=inet,inet6). It even seems to ignore the ipv6 address that we gave it. resolvconf does not seem to know how to handle it.

I would argue that this is an issue with ifupdown2 since it is not backwards-compatible with ifupdown - or do you recommend another setup (without resolvconf) for ifupdown2?

 

[fabian]

AFAICT your nameserver and search domain are static, why not just set them in /etc/resolv.conf instead of via ifupdown(2)?

 

[jaqxues]

That would work for our setup, I am just more concerned that the recommended setup does not work. Do you not think that this is an issue with ifupdown2?

 

[fabian]

possibly, while ifupdown2 tries to be compatible with ifupdown, it is not 100%. for PVE use cases it does not really matter - DNS settings are expected to be stable/static there, and not change dynamically. seems like the bookworm version of resolvconf got adapted to support ifupdown2 in any case: https://sources.debian.org/src/resolvconf/1.91+nmu1/debian/resolvconf.000resolvconf.if-up/

 

[jaqxues]

I checked bullseye for a change, but thanks for letting me know that it is available on bookworm! Will apply a patch and then upgrade to bookworm later.