動手學習TCP: 環境搭建

時間 2019-11-21

標籤動手學習 tcp 環境搭建欄目系統網絡简体版

原文原文鏈接

前一段時間經過Wireshark抓包，定位了一個客戶端和服務器之間數據傳輸的問題。最近就抽空看了看《TCP/IP詳解卷1》中關於TCP的部分，書中用了不少例子展現了TCP/IP協議中的一些基本概念。安全

因此，也準備本身動手，經過一些簡單的實驗來進一步瞭解一下TCP中的一些基本概念。服務器

環境搭建和配置

在開始進行實驗以前，首先看看實驗環境的搭建：網絡

Wireshark：用來抓取網絡上的包，能夠清楚的看到TCP/IP協議層，以及每層的詳細信息，經過此處下載
一臺虛擬機：若是客戶端和服務端都在本機，那麼數據通訊是不通過網卡的，因此Wireshark就抓不到任何數據包。方便的辦法就是本機安裝一個虛擬機，經過本機和虛擬機通訊進行實驗。我使用的是VirtualBox+winXP.
Pcap.Net：是一個WinPcap的.NET wrapper，基於這個庫，咱們就能夠很方便的經過C#代碼來實現下面功能（經過此處下載）：
1. 獲取網絡設備
2. 接收、解析數據包
3. 建立、發送數據包

在創建好實驗環境以後，還須要進行一些簡單的配置，保證宿主機和虛擬機之間的網絡是暢通的。併發

將虛擬機網絡設置爲"Host-only Adapter"模式。app

虛擬機網絡設置好以後，就能夠配置本機和虛擬機IP地址了，而後保證宿主機能夠ping通虛擬機。socket

環境驗證

經過上面的步驟，簡單的實驗環境就創建完成了，下面就要來實現客戶端和服務端了，試試實驗環境是否可以正常工做。tcp

服務端

首先，將虛擬機（192.168.56.102）做爲服務端，運行下面一段代碼建立一個簡單的socket server，服務端綁定192.168.56.102：8081：函數

import sys
from socket import *

HOST = "192.168.56.102"
PORT = 8081
BUFSIZ = 1024
ADDR = (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 data
    except Exception, e:
     print e
    conn.close()

客戶端

客戶端的實如今本機（192.168.56.101），使用一段基於Pcap.Net的代碼向服務器發送一個[SYN]包（TCP鏈接創建須要進行三次握手，[SYN]包就是第一個握手包），來請求創建TCP鏈接。工具

在客戶端代碼中，經過Pcap.Net實現了兩個工具函數，一個用來獲取本機網卡設備列表，一個用在構造不一樣類型的TPC包。ui

獲取本機網卡設備列表代碼：

public static PacketDevice GetNICDevice()
{
    // Retrieve the device list from the local machine
    IList<LivePacketDevice> allDevices = LivePacketDevice.AllLocalMachine;

    if (allDevices.Count == 0)
    {
        Console.WriteLine("No interfaces found! Make sure WinPcap is installed.");
        return null;
    }

    // Print the device list
    for (int i = 0; i != allDevices.Count; ++i)
    {
        LivePacketDevice device = allDevices[i];
        Console.Write((i + 1) + ". " + device.Name);
        if (device.Description != null)
            Console.WriteLine(" (" + device.Description + ")");
        else
            Console.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];
}

另外一段重要的代碼就是構造TCP包的代碼，根據OSI七層模型，下面代碼中分別建立了鏈路層、網絡層和傳輸層的部分，而後生成一個數據包：

public static Packet BuildTcpPacket(EndPointInfo endPointInfo, TcpControlBits tcpControlBits, List<TcpOption> 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，首先配置了客戶端和服務器的端口、IP/MAC地址信息，而後經過前面兩個工具函數構造一個TCP鏈接創建請求包（[SYN]包），並經過"VirtualBox Host-Only Network"網卡發送給服務端。

static void Main(string[] args)
{
    // Take the selected adapter
    PacketDevice selectedDevice = Utils.GetNICDevice();

    // Open the output device
    using (PacketCommunicator communicator = selectedDevice.Open(System.Int32.MaxValue, // name of the device
                                                                 PacketDeviceOpenAttributes.Promiscuous, // promiscuous mode
                                                                 1)) // 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 filter
            communicator.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 elapsed
                continue;
            case PacketCommunicatorReceiveResult.Ok:
                Utils.PacketInfoPrinter(packet);
                break;
            default:
                throw new InvalidOperationException("The result " + result + " should never be reached here");
        }
    } while (true);
}