Get local IP address of interface used to make a web service call within a Windows service
IPAddress[] localIPs = Dns.GetHostAddresses(Dns.GetHostName());

/// <summary>
/// Returns the IP Address of the given interface
/// </summary>
/// <param name="InterfaceName">Name of the interface</param>
/// <param name="AddressFamily">Address family to search for</param>
/// <returns>IPAddress of assinged IP address</returns>
public IPAddress GetIPAddress(string InterfaceName, System.Net.Sockets.AddressFamily AddressFamily)
{
    System.Net.NetworkInformation.NetworkInterface Interface = GetInterface(InterfaceName);
    if (Interface != null)
    {
        foreach (System.Net.NetworkInformation.UnicastIPAddressInformation IP in Interface.GetIPProperties().UnicastAddresses)
        {
            //Match address family
            if(IP.Address.AddressFamily != AddressFamily)
                continue;

            //Check for IPv6 conditions since we can easily have multiple IPs
            if(IP.Address.AddressFamily == System.Net.Sockets.AddressFamily.InterNetworkV6 && (IP.Address.IsIPv6LinkLocal || IP.AddressPreferredLifetime != uint.MaxValue || IP.AddressValidLifetime != uint.MaxValue))
                continue;

            //We've found the IP
            return IP.Address;
        }
    }

    return null;
}

/// <summary>
/// Returns the Network Interface for the given windows name
/// </summary>
/// <param name="InterfaceName">Interface name to get (ie Local Area Connection)</param>
/// <returns>Network Interface, or null if not found</returns>
System.Net.NetworkInformation.NetworkInterface GetInterface(string InterfaceName)
{
    if (InterfaceName == null || InterfaceName.Length == 0)
        return null;

    foreach (System.Net.NetworkInformation.NetworkInterface Interface in NetworkInterfaceArray)
    {
        if (Interface.Name == InterfaceName)
            return Interface;
    }

    return null;
}

public static List<string> DisplayDnsAddresses()
{
    var addresses = NetworkInterface.GetAllNetworkInterfaces()
        .Where(a => a.OperationalStatus == OperationalStatus.Up
                    && a.NetworkInterfaceType != NetworkInterfaceType.Loopback)
        .Select(a => a.GetIPProperties())
        .SelectMany(ipp => ipp.UnicastAddresses
            .Select(x => x.Address.ToString()));

    return addresses.ToList();
}