Synology Disk Station failed to update network config with new router

I have a Synology Disk Station DS411slim, which has been working flawlessly for almost two years; that is to say, that it has never crashed, corrupted data, failed to keep up with streaming demands etc.

The one issue I had was after I switched internet providers, and thus replaced my router. Everything seemed fine at first, the box used the same static IP address and was visible to my desktop devices. I only noticed something was wrong when I attempted to check for updates in DSM.

I logged into the box via SSH and found the issue after a quick poke around the system. The new router used a different IP to the old one (192.168.1.1 instead of 192.168.1.254) and the box had not updated this for either gateway or DNS. There may be a way to do this from within the DSM itself, but it was easy enough to resolve by hand.

Firstly, fix resolve.conf

Then fix the default route and make sure it uses the correct gateway even after a reboot

This should be all that is required to fix the problem, however, there are quite a few other files that hold a reference to the old router, so I updated these as well just to be neat.

After that the box was able to resolve hostnames and access the internet again, even after a reboot, and DSM updates worked correctly