A implementation of this paper: [A New Method for Symmetric NAT Traversal in UDP and TCP](http://www.goto.info.waseda.ac.jp/~wei/file/wei-apan-v10.pdf)
According to [RFC 3489](http://tools.ietf.org/html/rfc3478), a symmetric NAT is one where all requests from the same internal IP address and port, to a specific destination IP address and port, are mapped to the same external IP address and
port. If the same host sends a packet with the same source address and port, but to a different destination, a different mapping is used. Furthermore, only the external host that receives a packet can send a UDP packet back to the internal host.
So, if we know the port allocation rule of the Symmetric NAT, we can traverse Symmetric NAT. This paper proposes a new method for traversing Symmetric NAT which is based on port prediction and limited TTL values.
So, if we know the port allocation rule of the Symmetric NAT, we can traverse Symmetric NAT. This paper proposes a new method for traversing Symmetric NAT which is based on port prediction and limited TTL values.
It's just a experience project, I just wanna test whether UDP punching is possible if both nodes are behind symmetric NAT. To run it, you should run `punch_server.go` in a machine with public IP, so both nodes can connect to it to exchange info(just node info, not to relay like [RFC 6062](https://tools.ietf.org/html/rfc6062)), then run `nat_traversal [-s punch server] [-d id]` on both nodes, you can also specify other arguments, such as, STUN server by `-H` option, source IP by `-i`, source port by `-p`.
