Qt4.8如何通过QUdpSocket接收任何数据包，也就是嗅探DHCP

Qt4.8 how receive any packets aka sniff DHCP by QUdpSocket?

本文关键字：数据包也就是嗅探 DHCP 任何何通过 QUdpSocket Qt4 更新时间：2023-10-16

我正在尝试使用Qt4.8创建一个简单的DHCP客户端。

I Have two host:

ip地址为inet addr: 1.5.1.10 Bcast: 1.5.1.255掩码:255.255.255.0和isc-dhcp-server的服务器，向客户端发送以下参数:
```
IPs: 1.5.1.11-100 Bcast:1.5.255.255  Mask:255.255.0.0
```
客户端，参数派生于boot - inet地址:1.5.1.14 Bcast: 1.5.255.255掩码:255.255.0.0

在客户端上，我试图请求(在我的程序中)DHCP服务器提供新的选项。服务器已经发送了选项，但是我的程序无法从服务器接收任何数据，除了直接发送到客户端地址(1.5.1.14:68)的数据。

对于客户端，我编译了Open DHCP Locate，它工作得很好。当我在客户端运行tcpdump -i eth0 udp port 68 -e -n -vvvv -X时，它显示了来自服务器的数据包。我认为QUdpSocket需要一些参数来接收这些数据包。这些参数是什么呢?

我已经尝试创建我的套接字如下:

udpSocket = new QUdpSocket(this);
//udpSocket->bind(QHostAddress(QString("1.5.1.14")), 68);
qDebug() << "bind" << udpSocket->bind(QHostAddress::Any, 68, QUdpSocket::ShareAddress);
//qDebug() << "bind" << udpSocket->bind(QHostAddress::Broadcast, 68);
//qDebug() << "joinMulticastGroup" << udpSocket->joinMulticastGroup(QHostAddress(QString("1.5.255.255")));
//udpSocket->setMulticastInterface(QNetworkInterface::interfaceFromName(QString("eth0")));

//  int optval = 1;
//  qDebug() << "SO_BROADCAST" << setsockopt(udpSocket->socketDescriptor(), SOL_SOCKET, SO_BROADCAST, &optval, sizeof(optval));
//  const char dev[] = "eth0";
//  qDebug() << "SO_BINDTODEVICE" << setsockopt(udpSocket->socketDescriptor(), SOL_SOCKET, SO_BINDTODEVICE, dev, sizeof(dev) );

在各种组合中，但没有收到。

服务器端日志，命令为:

#tcpdump -i eth1 udp port 67 or port 68 -e -n -X

和

#dhcpdump -i eth1

.

    10:30:15.775100 84:eb:18:e8:59:b2 > ff:ff:ff:ff:ff:ff, ethertype IPv4 (0x0800), length 285: (tos 0x0, ttl 64, id 0, offset 0, flags [DF], proto UDP (17), length 271)
        1.5.1.14.68 > 255.255.255.255.67: [udp sum ok] BOOTP/DHCP, Request from 31:32:33:34:35:36, length 243, Flags [none] (0x0000)
              Client-Ethernet-Address 31:32:33:34:35:36
              Vendor-rfc1048 Extensions
                Magic Cookie 0x63825363
                DHCP-Message Option 53, length 1: Discover
            0x0000:  4500 010f 0000 4000 4011 37cc 0105 010e  E.....@.@.7.....
            0x0010:  ffff ffff 0044 0043 00fb 6dda 0101 0600  .....D.C..m.....
            0x0020:  0000 0000 0000 0000 0000 0000 0000 0000  ................
            0x0030:  0000 0000 0000 0000 3132 3334 3536 0000  ........123456..
            0x0040:  0000 0000 0000 0000 0000 0000 0000 0000  ................
            0x0050:  0000 0000 0000 0000 0000 0000 0000 0000  ................
            0x0060:  0000 0000 0000 0000 0000 0000 0000 0000  ................
            0x0070:  0000 0000 0000 0000 0000 0000 0000 0000  ................
            0x0080:  0000 0000 0000 0000 0000 0000 0000 0000  ................
            0x0090:  0000 0000 0000 0000 0000 0000 0000 0000  ................
            0x00a0:  0000 0000 0000 0000 0000 0000 0000 0000  ................
            0x00b0:  0000 0000 0000 0000 0000 0000 0000 0000  ................
            0x00c0:  0000 0000 0000 0000 0000 0000 0000 0000  ................
            0x00d0:  0000 0000 0000 0000 0000 0000 0000 0000  ................
            0x00e0:  0000 0000 0000 0000 0000 0000 0000 0000  ................
            0x00f0:  0000 0000 0000 0000 0000 0000 0000 0000  ................
            0x0100:  0000 0000 0000 0000 6382 5363 3501 01    ........c.Sc5..
    10:30:16.776570 10:fe:ed:05:f9:53 > 31:32:33:34:35:36, ethertype IPv4 (0x0800), length 342: (tos 0x10, ttl 128, id 0, offset 0, flags [none], proto UDP (17), length 328)
        1.5.1.10.67 > 1.5.1.33.68: [udp sum ok] BOOTP/DHCP, Reply, length 300, Flags [none] (0x0000)
              Your-IP 1.5.1.33
              Server-IP 1.5.1.10
              Client-Ethernet-Address 31:32:33:34:35:36
              Vendor-rfc1048 Extensions
                Magic Cookie 0x63825363
                DHCP-Message Option 53, length 1: Offer
                Server-ID Option 54, length 4: 1.5.1.10
                Lease-Time Option 51, length 4: 864000
                Subnet-Mask Option 1, length 4: 255.255.0.0
                Default-Gateway Option 3, length 4: 1.5.1.10
                BR Option 28, length 4: 1.5.255.255
                NTP Option 42, length 4: 1.5.1.10
                END Option 255, length 0
                PAD Option 0, length 0, occurs 20
            0x0000:  4510 0148 0000 0000 8011 3561 0105 010a  E..H......5a....
            0x0010:  0105 0121 0043 0044 0134 0c29 0201 0600  ...!.C.D.4.)....
            0x0020:  0000 0000 0000 0000 0000 0000 0105 0121  ...............!
            0x0030:  0105 010a 0000 0000 3132 3334 3536 0000  ........123456..
            0x0040:  0000 0000 0000 0000 0000 0000 0000 0000  ................
            0x0050:  0000 0000 0000 0000 0000 0000 0000 0000  ................
            0x0060:  0000 0000 0000 0000 0000 0000 0000 0000  ................
            0x0070:  0000 0000 0000 0000 0000 0000 0000 0000  ................
            0x0080:  0000 0000 0000 0000 0000 0000 0000 0000  ................
            0x0090:  0000 0000 0000 0000 0000 0000 0000 0000  ................
            0x00a0:  0000 0000 0000 0000 0000 0000 0000 0000  ................
            0x00b0:  0000 0000 0000 0000 0000 0000 0000 0000  ................
            0x00c0:  0000 0000 0000 0000 0000 0000 0000 0000  ................
            0x00d0:  0000 0000 0000 0000 0000 0000 0000 0000  ................
            0x00e0:  0000 0000 0000 0000 0000 0000 0000 0000  ................
            0x00f0:  0000 0000 0000 0000 0000 0000 0000 0000  ................
            0x0100:  0000 0000 0000 0000 6382 5363 3501 0236  ........c.Sc5..6
            0x0110:  0401 0501 0a33 0400 0d2f 0001 04ff ff00  .....3.../......
            0x0120:  0003 0401 0501 0a1c 0401 05ff ff2a 0401  .............*..
            0x0130:  0501 0aff 0000 0000 0000 0000 0000 0000  ................
            0x0140:  0000 0000 0000 0000

    ---------------------------------------------------------------------------

      TIME: 2016-09-19 10:30:15.853
        IP: 1.5.1.14 (84:eb:18:e8:59:b2) > 255.255.255.255 (ff:ff:ff:ff:ff:ff)
        OP: 1 (BOOTPREQUEST)
     HTYPE: 1 (Ethernet)
      HLEN: 6
      HOPS: 0
       XID: 00000000
      SECS: 0
     FLAGS: 0
    CIADDR: 0.0.0.0
    YIADDR: 0.0.0.0
    SIADDR: 0.0.0.0
    GIADDR: 0.0.0.0
    CHADDR: 31:32:33:34:35:36:00:00:00:00:00:00:00:00:00:00
     SNAME: .
     FNAME: .
    OPTION:  53 (  1) DHCP message type         1 (DHCPDISCOVER)
    OPTION:  54 (  4) Server identifier         1.5.1.10
    OPTION:  51 (  4) IP address leasetime      864000 (1w3d)
    ---------------------------------------------------------------------------
      TIME: 2016-09-19 10:30:16.855
        IP: 1.5.1.10 (10:fe:ed:5:f9:53) > 1.5.1.33 (31:32:33:34:35:36)
        OP: 2 (BOOTPREPLY)
     HTYPE: 1 (Ethernet)
      HLEN: 6
      HOPS: 0
       XID: 00000000
      SECS: 0
     FLAGS: 0
    CIADDR: 0.0.0.0
    YIADDR: 1.5.1.33
    SIADDR: 1.5.1.10
    GIADDR: 0.0.0.0
    CHADDR: 31:32:33:34:35:36:00:00:00:00:00:00:00:00:00:00
     SNAME: .
     FNAME: .
    OPTION:  53 (  1) DHCP message type         2 (DHCPOFFER)
    OPTION:  54 (  4) Server identifier         1.5.1.10
    OPTION:  51 (  4) IP address leasetime      864000 (1w3d)
    OPTION:   1 (  4) Subnet mask               255.255.0.0
    OPTION:   3 (  4) Routers                   1.5.1.10
    OPTION:  28 (  4) Broadcast address         1.5.255.255
    OPTION:  42 (  4) NTP servers               1.5.1.10

首先将套接字绑定到要通过的端口68上的接口。设置广播选项。通过writeDatagram将DHCP发现报文发送到广播地址(端口67)。然后，您只需等待对套接字的响应，使用readDatagram读取这些响应。

这应该是所有需要的。

如果你没有在合理的时间内得到回复，你当然需要能够处理超时。请记住UDP是不可靠的。

您的程序还需要以提升的权限运行，以便能够绑定到特权端口号。

解决方案是设置"broadcast"标志(在RFC 1542的3.1.1节和4.1.2节讨论)