Identify data being sent over socket

enum PacketType
{
    LoginData,
    OtherData
}

public interface IPacket
{
    PacketType PacketType { get; }
}

[Serializable]
public class LoginPacket : IPacket
{
    public PacketType PacketType { get { return PacketType.LoginData; } }
    public string Login { get; private set; }
    public string Password { get; private set; }

    public LoginPacket(string login, string password)
    {
        Login = login;
        Password = password;
    }
}

new LoginPacket("username", "password")

var receivedPacket = data as IPacket;
switch (receivedPacket.PacketType)
{
    case PacketType.LoginData:
        var loginPacket = data as LoginPacket;
        // check loginPacket.Login and .Password
        break;
    default:
        // other stuff
        break;
}