Qt4.8 如何通过 QUdpSocket 接收任何数据包又名嗅探 DHCP？

Question

我正在尝试使用 Qt4.8 创建一个简单的 DHCP 客户端。

我有两个主机：

IP 地址为 inet addr 的服务器：1.5.1.10 Bcast：1.5.1.255 Mask：255.255.255.0 和 isc-dhcp-server 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
```
具有启动时派生参数的客户端 - inet addr：1.5.1.14 Bcast：1.5.255.255 Mask：255.255.0.0

在客户端上，我试图（在我的程序中）向 DHCP 服务器询问新选项。服务器已发送选项，但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Open DHCP Locate and it works fine. When I run tcpdump -i eth0 udp port 68 -e -n -vvvv -X on client side, it shows a packet from the server. I think that QUdpSocket需要一些参数来接收这些数据包。这些参数是什么？

我试过这样创建套接字：

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) );

各种组合，但没有收到。

服务器端登录，cmds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

Answer 1

您首先将套接字绑定到您要通过其广播的接口，在端口 68 上。设置广播选项。发送 DHCP discovery packet to the broadcast address (port 67) using writeDatagram. And then you simply wait for replies to the socket, which you read with readDatagram.

这应该是所有需要的。

如果您没有在合理的时间内收到回复，您当然需要能够处理超时。请记住 UDP 是不可靠的。

您的程序还需要运行提升权限才能绑定到特权端口号。

Answer 2

解决方案是设置"broadcast"标志（在RFC 1542的第3.1.1和4.1.2节中讨论）

Qt4.8 如何通过 QUdpSocket 接收任何数据包又名嗅探 DHCP？

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

c++

sockets

qt

udp

broadcast