[2020]
Historical material is always welcome on HN and it's fun for readers to know what year an article dates from.
https://www.zerotier.com/blog/the-state-of-nat-traversal/
There are lots of others. The TS post is well written though, and contains some interesting information like the way the birthday paradox relates to punching symmetric NATS.
was thinking, traversing Nat is dead-simple