New answer, powershell
TCP
Get-Process -Id (Get-NetTCPConnection -LocalPort YourPortNumberHere).OwningProcess
UDP
Get-Process -Id (Get-NetUDPEndpoint -LocalPort YourPortNumberHere).OwningProcess
Old answer, cmd
C:\> netstat -a -b
(Add -n to stop it trying to resolve hostnames, which will make it a lot faster.)
Note Dane's recommendation for TCPView. It looks very useful!
-a Displays all connections and listening ports.
-b Displays the executable involved in creating each connection or listening port. In some cases well-known executables host multiple independent components, and in these cases the sequence of components involved in creating the connection or listening port is displayed. In this case the executable name is in [] at the bottom, on top is the component it called, and so forth until TCP/IP was reached. Note that this option can be time-consuming and will fail unless you have sufficient permissions.
-n Displays addresses and port numbers in numerical form.
-o Displays the owning process ID associated with each connection.
The question is trickier than it appears, because in many cases there isn't "an IP address for the local computer" so much as a number of different IP addresses. For example, the Mac I'm typing on right now (which is a pretty basic, standard Mac setup) has the following IP addresses associated with it:
fe80::1%lo0
127.0.0.1
::1
fe80::21f:5bff:fe3f:1b36%en1
10.0.0.138
172.16.175.1
192.168.27.1
... and it's not just a matter of figuring out which of the above is "the real IP address", either... they are all "real" and useful; some more useful than others depending on what you are going to use the addresses for.
In my experience often the best way to get "an IP address" for your local computer is not to query the local computer at all, but rather to ask the computer your program is talking to what it sees your computer's IP address as. e.g. if you are writing a client program, send a message to the server asking the server to send back as data the IP address that your request came from. That way you will know what the relevant IP address is, given the context of the computer you are communicating with.
That said, that trick may not be appropriate for some purposes (e.g. when you're not communicating with a particular computer) so sometimes you just need to gather the list of all the IP addresses associated with your machine. The best way to do that under Unix/Mac (AFAIK) is by calling getifaddrs() and iterating over the results. Under Windows, try GetAdaptersAddresses() to get similar functionality. For example usages of both, see the GetNetworkInterfaceInfos() function in this file.
Best Answer
You also have some other options, including your solution to "establish a network connection to a well-known IP and examine the socket's local IP address".
In that case (establishing network connection) however, that article points out that:
Amongst the other solutions:
Sys::Hostname
- works if it comes up with a resolvable hostname.