Question: What's the best way, using C# or other .NET language, to determine if a file path string is on the local machine or a remote server?

It's possible to determine if a path string is UNC using the following:

```
new Uri(path).IsUnc

```

That works great for paths that start with C:\ or other drive letter, but what about paths like:

```
\\machinename\sharename\directory
\\10.12.34.56\sharename\directory

```

...where both refer to the local machine - these are UNC paths but are still local.

Answer: 
This is how I did it.

```
    public static bool IsLocal(DirectoryInfo dir)
    {
        foreach (DriveInfo d in DriveInfo.GetDrives())
        {
            if (string.Compare(dir.Root.FullName, d.Name, StringComparison.OrdinalIgnoreCase) == 0) //[drweb86] Fix for different case.
            {
                return (d.DriveType != DriveType.Network);
            }
        }
         throw new DriveNotFoundException();
    }

```
The following should work for mapped drives and for UNC paths.

```
private static bool IsLocalPath(String path)
{
    if (!PathIsUNC(path))
    {
        return !PathIsNetworkPath(path);
    }

    Uri uri = new Uri(path);
    return IsLocalHost(uri.Host); // Refer to David's answer
}

[DllImport("Shlwapi.dll")]
[return: MarshalAs(UnmanagedType.Bool)]
static extern bool PathIsNetworkPath(String pszPath);

[DllImport("Shlwapi.dll")]
[return: MarshalAs(UnmanagedType.Bool)]
static extern bool PathIsUNC(String pszPath);

```