Get external IP address over remoting in C#

Question

I need to find out the external IP of the computer a C# application is running on.

In the application I have a connection (via .NET remoting) to a

Answer 1

You can basically parse the page returned by doing a WebRequest of http://whatismyipaddress.com

http://www.dreamincode.net/forums/showtopic24692.htm

Answer 2

This is one of those questions where you have to look deeper and maybe rethink the original problem; in this case, "Why do you need an external IP address?"

The issue is that the computer may not have an external IP address. For example, my laptop has an internal IP address (192.168.x.y) assigned by the router. The router itself has an internal IP address, but its "external" IP address is also internal. It's only used to communicate with the DSL modem, which actually has the external, internet-facing IP address.

So the real question becomes, "How do I get the Internet-facing IP address of a device 2 hops away?" And the answer is generally, you don't; at least not without using a service such as whatismyip.com that you have already dismissed, or doing a really massive hack involving hardcoding the DSL modem password into your application and querying the DSL modem and screen-scraping the admin page (and God help you if the modem is ever replaced).

EDIT: Now to apply this towards the refactored question, "How do I get the IP address of my client from a server .NET component?" Like whatismyip.com, the best the server will be able to do is give you the IP address of your internet-facing device, which is unlikely to be the actual IP address of the computer running the application. Going back to my laptop, if my Internet-facing IP was 75.75.75.75 and the LAN IP was 192.168.0.112, the server would only be able to see the 75.75.75.75 IP address. That will get it as far as my DSL modem. If your server wanted to make a separate connection back to my laptop, I would first need to configure the DSL modem and any routers inbetween it and my laptop to recognize incoming connections from your server and route them appropriately. There's a few ways to do this, but it's outside the scope of this topic.

If you are in fact trying to make a connection out from the server back to the client, rethink your design because you are delving into WTF territory (or at least, making your application that much harder to deploy).

Answer 3

Well, assuming you have a System.Net.Sockets.TcpClient connected to your client, you can (on the server) use client.Client.RemoteEndPoint. This will give you a System.Net.EndPoint pointing to the client; that should contain an instance of the System.Net.IPEndPoint subclass, though I'm not sure about the conditions for that. After casting to that, you can check it's Address property to get the client's address.

In short, we have

using (System.Net.Sockets.TcpClient client = whatever) {
    System.Net.EndPoint ep = client.Client.RemoteEndPoint;
    System.Net.IPEndPoint ip = (System.Net.IPEndPoint)ep;
    DoSomethingWith(ip.Address);
}

Good luck.

Answer 4

If you just want the IP that's bound to the adapter, you can use WMI and the Win32_NetworkAdapterConfiguration class.

http://msdn.microsoft.com/en-us/library/aa394217(VS.85).aspx

Answer 5

Patrik's solution works for me!

I made one important change. In process message I set the CallContext using this code:

// try to set the call context
LogicalCallContext lcc = (LogicalCallContext)requestMessage.Properties["__CallContext"];
if (lcc != null)
{
    lcc.SetData("ClientIP", ipAddr);
}

This places the ip address in the correct CallContext, so it can later be retrieved with GetClientIP().

Answer 6

The most reliable manner of doing this is checking a site like http://checkip.dyndns.org/ or similar, because until you actually go external to your network, you cannot find your external IP. However, hardcoding such a URL is asking for eventual failure. You may wish to only perform this check if the current IP looks like an RFC1918 private address (192.168.x.x being the most familiar of these.

Failing that, you can implement your own, similar, service sitting external to the firewall, so you will at least know if it's broken.