> 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).

Support for IPv6 is notoriously bad in residential modems. They can barely run IPv4. In an enterprise, you can do it properly. But here we are stuck with the junk the ISP gave out. Customers don't care. You have to work with what you've got.

I don't have enough time for that.