Is it the right flow for TCP hole punching for p2p application:

Question

1. Using stun I will get my external ip/port and NAT type.
2. On my middle server (public ip), I will register peers external ip/ports (Now server knows peer 1's and 2's external ip/port).
3. Exchange the ip/port (peer 1 will get to know the peer 2's ip/port).
4. Simultaneously make connect() call from both the peers.

Is it the right flow?

Answer 1

Your algorithm is correct for UDP. Take a look at these posts for more information:

• TCP Hole Punch (NAT Traversal) Library or something?
• UDP Hole Punching
• TCP Hole Punching

Answer 2

Hole punching with TCP is more complicated that what you have described. Have a look at the Practical JXTA II book available online at scribd for a description of the NAT traversal issues you would need to solve.