How to test if hostname refers to local machine

Question

Can anyone think of an easy way to tell in win32 or .NET if hostname (string) resolves to a local computer? Such as:

"myhostname"
"myhostname.mydomain.local"
"192.168.1.1"
"localhost"

The goal of this exercise is to produce a test which will tell if Windows security layer will treat access to machine as local or network

Answer 1

This question has already been answered, but here's what I came up with to resolve both host name and IP address:

public static bool IsLocalHost(string host)
{
    IPHostEntry localHost = Dns.GetHostEntry(Dns.GetHostName());

    IPAddress ipAddress = null;

    if (IPAddress.TryParse(host, out ipAddress))
        return localHost.AddressList.Any(x => x.Equals(ipAddress));

    IPHostEntry hostEntry = Dns.GetHostEntry(host);

    return localHost.AddressList.Any(x => hostEntry.AddressList.Any(y => x.Equals(y)));
}

Answer 2

In .NET you can:

IPHostEntry iphostentry = Dns.GetHostEntry (Dns.GetHostName ());

Then for any host name, check if it resolves to one of the IPs in iphostEntry.AddressList (this is an IPAddress[]).

Here is a full program that will check the host names/IP addresses passed in the command line:

using System;
using System.Net;

class Test {
    static void Main (string [] args)
    {
        IPHostEntry iphostentry = Dns.GetHostEntry (Dns.GetHostName ());
        foreach (string str in args) {
            IPHostEntry other = null;
            try {
                other = Dns.GetHostEntry (str);
            } catch {
                Console.WriteLine ("Unknown host: {0}", str);
                continue;
            }
            foreach (IPAddress addr in other.AddressList) {
                if (IPAddress.IsLoopback (addr) || Array.IndexOf (iphostentry.AddressList, addr) != -1) {
                    Console.WriteLine ("{0} IsLocal", str);
                    break;
                } 
            }
        }
    }
}