They clearly haven't talked to a telco or network device vendor, they would've sold them a VRF/EVPN/L3VPN based solution… for a whole bunch of money :)

You can DIY that these days though, plain Linux software stack, with optional hardware offload on some specific things and devices. Basically, you have a traffic distinguisher (VXLAN tunnel, MPLS label, SRv6, heck even GRE tunnel), keep a whole bunch of VRFs (man ip-vrf) around, and have your end services (server side) bind into appropriate VRFs as needed.

Also, yeah, with IPv6 you wouldn't have this problem. Regardless of whether it's GUAs or ULAs.

Also-also, you can do IPv6 on the server side until the NAT (which is in the same place as in the article), and have that NAT be a NAT64 with distinct IPv6 prefixes for each customer.

I recently just changed my default subnet to 10.X.Y.... rolling two random numbers to make it highly unlikely my home subnet through wireguard would conflict with the subnet where I am connecting from.

Why not IPv6? Pretending that it doesn't exist??

https://en.wikipedia.org/wiki/List_of_IPv6_transition_mechan...

The suggested solution involves using the CGNAT /10 in conjunction with a VPN, but I've actually seen someone do this, and still have problems with certain end users where their next hop for routing also involves a router with an IPv4 address in the same space, so it's not really bulletproof either. We may as well consider doing other naughty things like co-opting DoD non-routable /8s or the test net in the RFCs you're not supposed to use, because basically anything you pick is going to have problems.

This is basically what I use tailscale & their magicdns feature for. I manage a few locally hosted jellyfin servers for myself and some family members, and its the same problem. I just added tailscale to them all and now I can basically do ssh parents.jellyfin.ts.net or inlaws.jellyfin.ts.net

> But the moment two sites share the same address range, you have an ambiguity that IP routing cannot resolve.

Writing PF or nft rules to NAT these hyper-legacy subnets on the local side of the layer3 tunnel is actually super trivial, like 20 seconds of effort to reason about and write in a config manifest.

Like written the article, a device on the customer site is required. At that point you might as well deploy a router that has a supportable software stack and where possible sober IP instead of legacy IP.

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I have been running IPv6-only networks since 2005 and have been deploying IPv6-only networks since 2009. When I encountered a small implementation gap in my favorite BSD, I wrote and submitted a patch.

Anyone who complained about their favorite open source OS having an IPv6 implementation gap or was using proprietary software (and then also dumb enough to complain about it), should be ashamed of themselves for doing so on any forum with "hacker" in the name. But we all know they aren't ashamed of themselves because the competency crisis is very real and the coddle culture let's such disease fester.

There is no excuse to not deploy at minimum a dual-stack network if not an IPv6-only network. If you deploy an IPv4-only network you are incompetent, you are shitting up the internet for everyone else, and it would be better for all of humanity if you kept any and all enthusiasm you have for computers entirely to yourself (not a single utterance).

One step beyond this is the multi-subnetted network on each side. You get the DNAT working, but then suddenly the app gets more complex over time and suddenly you're calling 192.168.2.x, which leads to async routes. Some traffic works, some traffic works one way, and other traffic disappears.

Then you as the client/app manager pull your hair out as the network team tells you everything is working fine.

Can we please just use ipv6? PLEASE

Shameless plug - this is exactly the same problem that our team had when we had to maintain a bunch of our customer's servers. All of the subnets were same, and we had to jump through hoops just to access those servers - vpns, port forwarding, dynamic dns with vnc - we've tried it all. That is why we developed https://sshreach.me/ - now it's a click of a button.