default route not saved when configuring a static IP

I'm not sure if I'm running across the same issue as you but i have just been trying to re-create your issue and can, sort of... (Although on reflection I think it may be something different altogether...)

I have set up a new TKL v13.0 (x64) LAMP instance on my PVE server and gave it 3 different (virtual) NICs. Here is what I found:

• Once it reboots (after install) it won't autoconfigure networking.
• Manually trying DHCP (from ConfConsole) complains that it was unable to get a lease.
• Manual/static config appears to work but the IP is unreachable externally (although internally it seems to be ok).
• Unlike you, the Gateway IP sticks (and displays ok) but is unreachable via ping from within the VM.
• ifup and ifdown both produce no errors (and appear to work fine - doesn't resolve networking issues though...)

I double checked by creating another new VM (the same except with a single NIC) and that works fine. So unfortunately I was not able to confirm whether this is an issue with my hypervisor (Proxmox) or the TKL appliance itself.

Sorry despite my best efforts, I don't think that I am very much help to you on this one...

[update] I just had a brainwave and deleted all 3 vNICs from my test server and readded 2 (but this time used just default PVE settings). It all now works as expected (DHCP works as does setting a static IP). To be extra sure I stopped the VM and added 2 move vNICs (total of 4) and again all is fine (although by default the 4th had to be initialised). Following that I think that we can safely say that the v13.0 ConfConsole works ok with multiple NICs (at least under some circumstance). Considering your other errors I can't help but think that perhaps this is a hardware and/or driver and/or networking issue of some sort...

TBH I have never had that issue, but I also usually use OVZ templates (so ConfConsole doesn't work anyway...). Regardless of the fact that ConfConsole should work (and shouldn't remove values that are ok) if the correct values are in the relevant files (you mentioned '/etc/network/interfaces' is correct) then it should work regardless of what ConfConsole is displaying... AFAIK ConfConsole merely adjusts these values (in their relevant config files) rather than overriding the configs (otherwise you wouldn't be able to manually set them...). This would suggest to me that your problem runs deeper than an issue with ConfConsole...

SO, like I say, it seems to me that you have some other issue somewhere... Perhaps there is something stopping your server contacting the gateway (like a firewall or some other networking issue)? Can you ping the desired gateway IP from within the TKL appliance? Perhaps something to test would be to reset networking to DHCP and see what gateway your appliance picks up from that...?

Also FWIW (you probably are already all over this but just in case) the Debian Networking Docs are relevant.

The links in that thread you used point to Squeeze packages (i.e. for TKL v12.x). Assuming you are using TKL v13 there are probably newer packages. Although I doubt very much that is the cause of your issue...

I'm assuming that you are using ConfConsole to set your static IP? Or are you doing it some other way?

Sorry that no one was along to help you sooner, but I'm super glad that you got it worked out! :)

FWIW seeing as the Backports package works then you can almost guarantee that it will work OOTB under the new version of Debian (which TKL v14 will eventually be based on - a long way away yet...).