Multiple NICs and networking service error

[dafydd]

I have a Proxmox v6 server (not quite ready to upgrade to 7 on this server yet). I've setup a new CT with a Debian 11 template.

I then added a second IP address on eth1, using the same gateway. This all works, with the second IP working and visible. But 'networking.service' is showing as failed:

Feb 13 15:37:41 core ifup[108]: RTNETLINK answers: File exists Feb 13 15:37:41 core ifup[55]: ifup: failed to bring up eth1 Feb 13 15:37:41 core systemd[1]: networking.service: Main process exited, code=exited, status=1/FAILURE Feb 13 15:37:41 core systemd[1]: networking.service: Failed with result 'exit-code'. Feb 13 15:37:41 core systemd[1]: Failed to start Raise network interfaces.

I'm just wondering what this problem is here, even though it appears to work correctly.

As an aside, I have arpwatch running on this network, and it shows that this second IP address is flipping back and forth between the MAC address of eth0 and eth1. It's doing this constantly every 15 minutes since I added the extra IP.

 

[dafydd]

The error goes away when I remove the gateway on eth1. For some reason when I tried this before, it didn't appear to work e.g. the second IP didn't appear to be routable. But it works now anyway.
Edit: Unfortuntely the MAC address flip-flopping is still happening.