Xaqron Xaqron -4 years ago 44
C# Question

What is IP address '::1'?

I was playing with sockets on local machine with no network connection. See below:

IPAddress address = IPAddress.Any; // doesn't work
IPAddress address = IPAddress.Parse("::1"); // works

So what is exactly
IP address ? Is it the default available IP address or it's the loopback address ? what happens to above code (working line) on a machine with dedicated IP address and network connection ?


exact code is used to bind a specific IP address to socket. Here it is:

ServicePoint sp = ServicePointManager.FindServicePoint(uri);
sp.BindIPEndPointDelegate = new BindIPEndPoint(Bind);
// here's the bind delegate:
private IPEndPoint Bind(ServicePoint sp, IPEndPoint ep, int retryCount)
return new IPEndPoint(IPAddress.Parse("::1"), 0);

Answer Source

::1 is the loopback address in IPv6. Think of it as the IPv6 version of

See http://en.wikipedia.org/wiki/Localhost

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