Get a machines MAC address on the local network from its IP in C#

Question

I am trying write a function that takes a single IP address as a parameter and queries that machine on my local network for it\'s MAC address.

Answer 1

Just a better performing version of the accepted method.

    public string GetMacByIp( string ip )
    {
        var pairs = this.GetMacIpPairs();

        foreach( var pair in pairs )
        {
            if( pair.IpAddress == ip )
                return pair.MacAddress;
        }

        throw new Exception( $"Can't retrieve mac address from ip: {ip}" );
    }

    public IEnumerable GetMacIpPairs()
    {
        System.Diagnostics.Process pProcess = new System.Diagnostics.Process();
        pProcess.StartInfo.FileName = "arp";
        pProcess.StartInfo.Arguments = "-a ";
        pProcess.StartInfo.UseShellExecute = false;
        pProcess.StartInfo.RedirectStandardOutput = true;
        pProcess.StartInfo.CreateNoWindow = true;
        pProcess.Start();

        string cmdOutput = pProcess.StandardOutput.ReadToEnd();
        string pattern = @"(?([0-9]{1,3}\.?){4})\s*(?([a-f0-9]{2}-?){6})";

        foreach( Match m in Regex.Matches( cmdOutput, pattern, RegexOptions.IgnoreCase ) )
        {
            yield return new MacIpPair()
            {
                MacAddress = m.Groups[ "mac" ].Value,
                IpAddress = m.Groups[ "ip" ].Value
            };
        }
    }

    public struct MacIpPair
    {
        public string MacAddress;
        public string IpAddress;
    }