动手学习TCP系列之环境搭建

动手学习TCP系列之环境搭建环境搭建和配置在开始进行实验之前，首先看看实验环境的搭建：Wireshark：用来抓取网络上的包，可以清楚的看到TCP/IP协议层，以及每层的详细信息，通过此处下载一台虚拟机：如果客户端和服务端都在本机，那么数据通信是不经过网卡的，所以Wireshark 就抓不到任何数据包。

方便的办法就是本机安装一个虚拟机，通过本机和虚拟机通信进行实验。

我使用的是VirtualBox+winXP.：是一个WinPcap的.NET wrapper，基于这个库，我们就可以很方便的通过C#代码来实现下面功能(通过此处下载)：获取网络设备接收、解析数据包创建、发送数据包在建立好实验环境之后，还需要进行一些简单的配置，保证宿主机和虚拟机之间的网络是畅通的。

将虚拟机网络设置为"Host-only Adapter"模式。

虚拟机网络设置好之后，就可以配置本机和虚拟机IP地址了，然后保证宿主机可以ping通虚拟机。

环境验证通过上面的步骤，简单的实验环境就建立完成了，下面就要来实现客户端和服务端了，试试实验环境是否能够正常工作。

服务端首先，将虚拟机(192.168.56.102)作为服务端，运行下面一段代码创建一个简单的socket server，服务端绑定192.168.56.102：8081：import sysfrom socket import *HOST = "192.168.56.102"PORT = 8081BUFSIZ = 1024ADDR = (HOST, PORT)server = socket(AF_INET, SOCK_STREAM)print "Socket created"try:server.bind(ADDR)except error, msg:print 'Bind failed. Error Code : ' + str(msg[0]) + ' Message ' + msg[1] sys.exit()server.listen(10)print 'Socket now listening'while True:conn, addr = server.accept()try:data = conn.recv(100)if data:print dataexcept Exception, e:print econn.close()客户端客户端的实现在本机(192.168.56.101)，使用一段基于的代码向服务器发送一个[SYN]包(TCP连接建立需要进行三次握手，[SYN]包就是第一个握手包)，来请求建立TCP连接。

在客户端代码中，通过实现了两个工具函数，一个用来获取本机网卡设备列表，一个用在构造不同类型的TPC包。

获取本机网卡设备列表代码：public static PacketDevice GetNICDevice(){// Retrieve the device list from the local machineIList allDevices = LivePacketDevice.AllLocalMachine;if (allDevices.Count == 0){Console.WriteLine("No interfaces found! Make sure WinPcap is installed.");return null;}// Print the device listfor (int i = 0; i != allDevices.Count; ++i){LivePacketDevice device = allDevices[i];Console.Write((i + 1) + ". " + );if (device.Description != null)Console.WriteLine(" (" + device.Description + ")");elseConsole.WriteLine(" (No description available)");}int deviceIndex = 0;do{Console.WriteLine("Enter the interface number (1-" + allDevices.Count + "):");string deviceIndexString = Console.ReadLine();if (!int.TryParse(deviceIndexString, out deviceIndex) || deviceIndex < 1 || deviceIndex > allDevices.Count){deviceIndex = 0;}} while (deviceIndex == 0);return allDevices[deviceIndex - 1];}另一段重要的代码就是构造TCP包的代码，根据OSI七层模型，下面代码中分别创建了链路层、网络层和传输层的部分，然后生成一个数据包：public static Packet BuildTcpPacket(EndPointInfo endPointInfo, TcpControlBits tcpControlBits, List tcpOptionList = null){EthernetLayer ethernetLayer =new EthernetLayer{Source = new MacAddress(endPointInfo.SourceMac),Destination = new MacAddress(endPointInfo.DestinationMac), EtherType = EthernetType.None, // Will be filled automatically. };IpV4Layer ipV4Layer =new IpV4Layer{Source = new IpV4Address(endPointInfo.SourceIp),CurrentDestination = new IpV4Address(endPointInfo.DestinationIp), Fragmentation = IpV4Fragmentation.None,HeaderChecksum = null, // Will be filled automatically.Identification = 123,Options = IpV4Options.None,Protocol = null, // Will be filled automatically.Ttl = 10,TypeOfService = 0,};TcpLayer tcpLayer =new TcpLayer{SourcePort = endPointInfo.SourcePort,DestinationPort = endPointInfo.DestinationPort,Checksum = null, // Will be filled automatically.SequenceNumber = seqNum,AcknowledgmentNumber = ackNum,ControlBits = tcpControlBits,Window = windowSize,UrgentPointer = 0,Options = (tcpOptionList == null) ? TcpOptions.None : new TcpOptions(tcpOptionList),};PacketBuilder builder = new PacketBuilder(ethernetLayer, ipV4Layer, tcpLayer);return builder.Build(DateTime.Now);}主程序中，首先配置了客户端和服务器的端口、IP/MAC地址信息，然后通过前面两个工具函数构造一个TCP连接建立请求包([SYN]包)，并通过"VirtualBox Host-Only Network"网卡发送给服务端。

static void Main(string[] args){// Take the selected adapterPacketDevice selectedDevice = Utils.GetNICDevice();// Open the output deviceusing (PacketCommunicator communicator = selectedDevice.Open(System.Int32.MaxValue, // name of the device PacketDeviceOpenAttributes.Promiscuous, // promiscuous mode1)) // read timeout{EndPointInfo endPointInfo = new EndPointInfo();endPointInfo.SourceMac = "08:00:27:00:C0:D5";endPointInfo.DestinationMac = "08:00:27:70:A6:AE";endPointInfo.SourceIp = "192.168.56.101";endPointInfo.DestinationIp = "192.168.56.102";endPointInfo.SourcePort = 3330;endPointInfo.DestinationPort = 8081;using (BerkeleyPacketFilter filter = communicator.CreateFilter("tcp port " + endPointInfo.DestinationPort)){// Set the filtercommunicator.SetFilter(filter);}communicator.SendPacket(Utils.BuildTcpPacket(endPointInfo, TcpControlBits.Synchronize, null));PacketHandler(communicator, endPointInfo);}Console.WriteLine("Press Enter to Quit!");Console.ReadLine();}private static void PacketHandler(PacketCommunicator communicator, EndPointInfo endPointInfo){Packet packet = null;do{PacketCommunicatorReceiveResult result = communicator.ReceivePacket(out packet);switch (result){case PacketCommunicatorReceiveResult.Timeout:// Timeout elapsedcontinue;case PacketCommunicatorReceiveResult.Ok:Utils.PacketInfoPrinter(packet);break;default:throw new InvalidOperationException("The result " + result + " shouldnever be reached here");}} while (true);}运行代码代码完成了，下面看看运行效果，为了直观的看到数据包的传输，这是就可以打开Wireshark 了。