Hopefully the title makes sense; I have a server currently in a colo facility, with many IP addresses routed to it. They are individual IPs and not in a contiguous block.

Due to vastly improved connectivity (fibre) at home I am slowly bringing my infrastructure in-house for managability and eventually, cost savings. What I would like to do though is use the IP addresses allocated to my existing server, at home. I have an IP block allocated to me on my new ISP connection, but for a couple of reasons I'd like to make use of the colo ones for now:

1. Ease of transition - lots of domains, dns, hard-coded IPs in programs, etc.

2. Connectivity fallback. If my primary line goes down and switches to fallback 1 (dsl) or fallback 2 (4G), I lose access to the ISP-allocated IP block of IPs that are only presented on the primary WAN interface.

What I'd like to achieve is my home virtualisation server (Proxmox/Debian-based) "dials in" to the colo server in the colo facility (also Proxmox/Debian) via VPN or similar, and gets to make use of the IP addresses that currently terminate on the colo box. If the primary connection to my ISP goes down and one of the fallback routes kicks in, the VPN tunnel will just time out and then be re-established on the backup connection instead.

I'm sure this is doable, but I have no idea how. I'm not afraid to get my hands dirty, I just don't really know where to start?