Afaik you need some external resource to coordinate the punch. The STUN protocol is purpose built for this, and both clients need to be able to reach a STUN server to coordinate which port and public IP they’ll try to connect to each other on. I assume this does something similar but with p2p network tech instead of a STUN server.

Sir this is a Wendy’s

I know this was controversial over at /r/BodyWeightFitness, but I had some good results with nick-e’s BWSF program. I did eventually need to modify it and split it up into an A/B routine because doing the full program took too long for me, but what nick-e put together is a really great resource. https://nick-e.com/bwsf/