TCP Hole Punch (NAT Traversal) Library or something?

Question

I want to do TCP Hole Punching (NAT Traversal) in C#. It can be done with a rendezvous server if needed. I found http://sharpstunt.codeplex.com/ but can not get this to work. Ideally i need some method which i give a Port Number (int) as parameter that after a call to this method is available ("Port Forwarded") at the NAT. It would be also OK if the method just returns some port number which is then available at the NAT. Has anybody done this in C# ? Can you give me working examples for sharpstunt or something else?

Answer 1

The question is quite old but for anyone looking at an alternate solution for NAT Traversal, you should take a look at the Open.NAT project. It's really easy to use and work with both UPNP and PMP, but it's different than Hole Punching.

Let's say that you want to forward external Port 1700 to local port 1600, all you have to do is:

var discoverer = new NatDiscoverer();
var device = await discoverer.DiscoverDeviceAsync();
await device.CreatePortMapAsync(new Mapping(Protocol.Tcp, 1600, 1700, "The mapping name"));

You can also list all existing mappings, so you can validate that your port is not already used.

var sb = new StringBuilder();
var ip = await device.GetExternalIPAsync();

sb.AppendFormat("\nAdded mapping: {0}:1700 -> 127.0.0.1:1600\n", ip);
sb.AppendFormat("\n+------+-------------------------------+--------------------------------+------------------------------------+-------------------------+");
sb.AppendFormat("\n| PROT | PUBLIC (Reacheable)           | PRIVATE (Your computer)        | Descriptopn                        |                         |");
sb.AppendFormat("\n+------+----------------------+--------+-----------------------+--------+------------------------------------+-------------------------+");
sb.AppendFormat("\n|      | IP Address           | Port   | IP Address            | Port   |                                    | Expires                 |");
sb.AppendFormat("\n+------+----------------------+--------+-----------------------+--------+------------------------------------+-------------------------+");
foreach (var mapping in await device.GetAllMappingsAsync())
{
    sb.AppendFormat("\n|  {5} | {0,-20} | {1,6} | {2,-21} | {3,6} | {4,-35}|{6,25}|",
        ip, mapping.PublicPort, mapping.PrivateIP, mapping.PrivatePort, mapping.Description, mapping.Protocol == Protocol.Tcp ? "TCP" : "UDP", mapping.Expiration.ToLocalTime());
}
sb.AppendFormat("\n+------+----------------------+--------+-----------------------+--------+------------------------------------+-------------------------+");
Console.WriteLine(sb.ToString());

There is also a blog post about NAT Traversal on MSDN: https://blogs.msdn.microsoft.com/ncl/2009/07/27/end-to-end-connectivity-with-nat-traversal/

Answer 2

We put together a library called IceLink that does P2P streaming using ICE/STUN/TURN with full NAT traversal. STUN-based hole-punching works for the majority of routers to establish a direct connection between peers, and for the "bad" routers out there, the connection falls back to a TURN-based relay.

Answer 3

http://sipsorcery.codeplex.com has a working stun server.

SipSorcery.core -> SipSorcery.Net -> Stun

Answer 4

It sounds like you might be getting TCP and UDP mixed up. TCP is a connection-orientated protocol, easily understood by firewalls and routers, and requires one initiator (client) and one listener (server). If both client and server are behind firewalls or NAT, you cannot punch a hole through without having them both connect to some proxy server (which is not firewalled). The problem with this is that then the proxy would be responsible for relaying all of their traffic.

From your question, it sounds like you are more interested in UDP hole punching, which exploits the fat that UDP is stateless, and not connection-orientated. Therefore most state-tracking firewalls will make a "best guess" about the UDP data flow, and assume that traffic leaving on a given port will receive replies on the same port, and automatically route them back. If, using some out-of-channel means (such as a TCP server which simply passes addresses and not data), both peers can be transmitting data to each other on the same ports, their respective firewalls/NAT routers will open up holes allowing the traffic in.

As for how to do it, it all depends on how you are going to get the IP address of the peers to each other. Once you have it, simply start transmitting UDP packets on an agreed port, and wait for a reply.