> It’s the same assumption is required for any hole punching handshake (including STUN).

This is incorrect.

Hole punching requires being able to predict external port. That's it. If the port remains the same, it certainly simplifies things, but ports going up (or down) by 1 (or 2, or 5) with each new mapping is quite common, trivial to detect and to punch through.

I wonder how many new technical terms are going to be created by LLMs - not to say that this post was N necessarily written by an LLM (but, who knows!)

It comes from academic papers on categorizing NAT behaviors which (trust me) is hardly the page turning research most people are used to. In these papers they talk about patterns NATs use between successive external port allocations -- which they call the "delta."

The name "equal delta" just means a type of NAT with a delta that tries to preserve the source port. Not to be confused with "preserving" type deltas (that preserve "the same numerical distance" between successive mappings -- e.g. a "preserving delta" type with a value of +1 means each successive NAT allocation is one more than the previous.)

Edit: It took me a while but I am pretty sure this was the original paper that goes into mapping allocations. https://www.usenix.org/legacy/events/imc05/tech/full_papers/...

In my mind there was a neat table with named deltas and examples but maybe that was what I pulled from the text.

>equal delta mapping

Very clearly a hallucination