TCP hole punching for Bitcoin nodes behind home NATs?

Network Address Translation (NAT) typically maintains a mapping between an internal IP:port and an external IP:port for as long as the NAT device considers the session active. This allows multiple connections from the same internal endpoint to use the same mapping, provided the mapping is not terminated by the NAT itself.

If there were a requirement to change this behavior so that each connection creates a new mapping or causes the previous one to become invalid, a different design approach would be necessary. One possible method could involve implementing logic within the NAT device to expire or invalidate a mapping immediately after the first successful connection has been established and then closed, forcing subsequent connections to negotiate a new mapping. Such a design would require stateful tracking of connection lifecycles and potentially impact performance or introduce complexity in managing concurrent sessions.

Developing this kind of system would demand careful consideration of both security implications and application compatibility, as many existing protocols assume stable NAT mappings for multiple sequential or parallel connections. Extensive testing and documentation would also be essential to ensure predictable network behavior and to inform users of any deviations from standard NAT operations.