永远不会收到发送到localhost上的端口的数据包

Question

我正在开发一个使用PcapPlusPlus的Linux应用程序，它将向本地主机上的一个端口发送一个SIP包。基本上，它是在发送UDP消息：

Source:  127.0.0.1 port 5061 
Dest:    127.0.0.1 port 5060

我的问题是为什么端口5060看不到数据。

以下是C++代码的一部分：

    string localhost = "127.0.0.1";
    PcapLiveDevice *dev = pcpp::PcapLiveDeviceList::getInstance().getPcapLiveDeviceByIp(localhost.c_str());

    if (!dev->open())
            printf("open device failed\n");

    int res = dev->sendPacket(&packet);
    printf("%d return code\n", res);

sendPacket()返回了1，因此发送看起来不错。应用程序是以root用户身份运行的，因此它应该不会有原始套接字的权限问题。

Wireshark显示正在发送的数据，但运行在端口5060上的服务器永远看不到该数据。我还验证了netcat看不到它，所以它看起来不是服务器的问题。

以下是Wireshark跟踪：

Frame 415: 556 bytes on wire (4448 bits), 556 bytes captured (4448 bits) on interface 0
    Interface id: 0 (any)
        Interface name: any
    Encapsulation type: Linux cooked-mode capture (25)
    Arrival Time: Jan  2, 2020 15:15:44.960061179 CST
    [Time shift for this packet: 0.000000000 seconds]
    Epoch Time: 1577999744.960061179 seconds
    [Time delta from previous captured frame: 24.812597478 seconds]
    [Time delta from previous displayed frame: 24.812597478 seconds]
    [Time since reference or first frame: 1328.602949365 seconds]
    Frame Number: 415
    Frame Length: 556 bytes (4448 bits)
    Capture Length: 556 bytes (4448 bits)
    [Frame is marked: False]
    [Frame is ignored: False]
    [Protocols in frame: sll:ethertype:ip:udp:sip:sdp]
    [Coloring Rule Name: UDP]
    [Coloring Rule String: udp]
Linux cooked capture
    Packet type: Unicast to us (0)
    Link-layer address type: 772
    Link-layer address length: 6
    Source: 00:00:00_00:00:00 (00:00:00:00:00:00)
    Unused: 0006
    Protocol: IPv4 (0x0800)
Internet Protocol Version 4, Src: 127.0.0.1, Dst: 127.0.0.1
    0100 .... = Version: 4
    .... 0101 = Header Length: 20 bytes (5)
    Differentiated Services Field: 0x00 (DSCP: CS0, ECN: Not-ECT)
        0000 00.. = Differentiated Services Codepoint: Default (0)
        .... ..00 = Explicit Congestion Notification: Not ECN-Capable Transport (0)
    Total Length: 540
    Identification: 0x014d (333)
    Flags: 0x4000, Don't fragment
        0... .... .... .... = Reserved bit: Not set
        .1.. .... .... .... = Don't fragment: Set
        ..0. .... .... .... = More fragments: Not set
        ...0 0000 0000 0000 = Fragment offset: 0
    Time to live: 64
    Protocol: UDP (17)
    Header checksum: 0x3982 [validation disabled]
    [Header checksum status: Unverified]
    Source: 127.0.0.1
    Destination: 127.0.0.1
User Datagram Protocol, Src Port: 5061, Dst Port: 5060
    Source Port: 5061
    Destination Port: 5060
    Length: 520
    Checksum: 0xeedb [unverified]
    [Checksum Status: Unverified]
    [Stream index: 0]
Session Initiation Protocol (INVITE)

我可以使用netcat成功地将数据发送到端口5060 (发送端的nc 127.0.0.1 5060，接收端的nc -lv 127.0.0.1 5060 )，所以看起来没有任何防火墙问题。我尝试使用一个开源的sipp客户端，服务器收到了来自它的消息。我比较了来自sipp客户端和我的应用程序的Wireshark数据，它们是相同的(除了序列号和校验和)。你知道为什么我的应用会有不同的结果吗？谢谢!

编辑-尝试连接到远程计算机上的服务器时也会出现同样的问题。

Answer 1

我找到问题了。传出数据包中的src和dest设置不正确。