Linux C++ IPv6 UDP 多播发送失败并出现错误 EADDRNOTAVAIL (99) 无法分配请求的地址

Question

我正在尝试发送 IPv6 UDP 多播消息。

下面的部分测试代码显示了两个部分，一个用于发送 IPv6 组播消息，另一个用于发送 IPv4 组播消息。

IPv4 的代码工作正常。

用于 IPv6 的代码在 sendto 中总是失败，返回 EADDRNOTAVAIL (99) 无法分配请求的地址。

...

  if (ipV6Select)
  {
    // Create IPv6 DGRAM Socket
    int sock = socket(AF_INET6, SOCK_DGRAM, 0);
    if (sock < 0)
      throw OIP::OipException(OIP_SOCK_ACTION_FAILED("Cannot set socket option IPV6 socket, socket function failed with retVal " <<
                                                      sock << " (errno=" << strerror(errno) << " (" << errno << ")."));

    // Register multicast interface.
    int ifIdx{static_cast<int>(if_nametoindex("svlan1_260"))};
    std::cout << "Temp:ifIdx=" << ifIdx << std::endl;
    std::lock_guard<std::mutex> lockGuard(setSockoptMutex);
    retVal = setsockopt(sock, IPPROTO_IPV6, IPV6_MULTICAST_IF, &ifIdx, sizeof(ifIdx));
    if (retVal < 0)
       throw OIP::OipException(OIP_SOCK_ACTION_FAILED("Cannot set socket option IPV6_MULTICAST_IF, setsockopt function failed with retVal " <<
                                                      retVal << " (errno=" << strerror(errno) << " (" << errno << ")."));

    // Create IPv6 address.
    struct sockaddr_in6 sockAddrIpV6{};
    sockAddrIpV6.sin6_family = {AF_INET6};
    sockAddrIpV6.sin6_port = {htons(2020)};
    sockAddrIpV6.sin6_scope_id = {static_cast<uint32_t>(ifIdx)};
    inet_pton(AF_INET6, "FF02:0000:0000:0000:0000:0000:0000:00FE", &sockAddrIpV6.sin6_addr);

    std::cout << "IPV6 Send: family=" << sockAddrIpV6.sin6_family << ", sin6_port=" << sockAddrIpV6.sin6_port  << ", sin6_scope_id=" << sockAddrIpV6.sin6_scope_id
              << ", addr=FF02:0000:0000:0000:0000:0000:0000:00FE" << std::endl;


    // Send message to socket.
    retVal = sendto(sock,
                    sendMsgCharBufVect.data(),
                    sendMsgCharBufVect.size(),
                    0,
                    reinterpret_cast<struct sockaddr*>(&sockAddrIpV6),
                    sizeof(struct sockaddr_in6));
    if (retVal < 0)
      throw OIP::OipException(OIP_SOCK_ACTION_FAILED("IPV6 Socket send data (socket sendto function) failed with retVal " << retVal <<
                                                      " (errno=" << strerror(errno) << " (" << errno << "))."));
  }

  // Send IPV4 multicast message.
  else
  {
    // Create IPv4 DGRAM Socket
    std::string ipV4Str{"239.0.0.254"};
    int sock = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);
    if (sock < 0)
      throw OIP::OipException(OIP_SOCK_ACTION_FAILED("Cannot set socket option IPV4 socket, socket function failed with retVal " <<
                                                      sock << " (errno=" << strerror(errno) << " (" << errno << ")."));

    // Register multicast interface.
    struct ip_mreqn mreqn{};
    inet_aton(ipV4Str.c_str(), &mreqn.imr_multiaddr);
    mreqn.imr_ifindex        = {static_cast<int>(if_nametoindex("svlan1_260"))};
    retVal = setsockopt(sock, IPPROTO_IP, IP_MULTICAST_IF, &mreqn, sizeof(mreqn));
    if (retVal < 0)
       throw OIP::OipException(OIP_SOCK_ACTION_FAILED("Cannot set socket option IP_MULTICAST_IF, setsockopt function failed with retVal " <<
                                                      retVal << " (errno=" << strerror(errno) << " (" << errno << ")."));

    // Create IPv4 address.
     struct sockaddr_in sockAddrIpV4{};
     sockAddrIpV4.sin_family = {AF_INET};
     sockAddrIpV4.sin_port = {htons(2020)};
     inet_aton(ipV4Str.c_str(), &sockAddrIpV4.sin_addr);

     std::cout << "IPV4 Send: family=" << sockAddrIpV4.sin_family << ", sin_port=" << sockAddrIpV4.sin_port  << ", addr=" << std::hex << sockAddrIpV4.sin_addr.s_addr<< std::dec <<std::endl;

     // Send message to socket.
     retVal = sendto(sock,
                     sendMsgCharBufVect.data(),
                     sendMsgCharBufVect.size(),
                     0,
                     reinterpret_cast<struct sockaddr*>(&sockAddrIpV4),
                     sizeof(struct sockaddr_in));
     if (retVal < 0)
       throw OIP::OipException(OIP_SOCK_ACTION_FAILED("IPV4 Socket send data (socket sendto function) failed with retVal " << retVal <<
                                                      " (errno=" << strerror(errno) << " (" << errno << "))."));
  }

...

tcpdump IPv4 显示带有请求地址的传出多播消息：

2020-04-02 23:30:19.384892 00:60:1d:7d:08:07 (oui Unknown) > 01:00:5e:00:00:fe (oui Unknown), ethertype 802.1Q (0x8100), length 90: vlan 260, p 0, ethertype IPv4, (tos 0x0, ttl 1, id 54916, offset 0, flags [none], proto UDP (17), length 72)
    100.5.81.1.38790 > 239.0.0.254.2020: UDP, length 44
        0x0000:  0100 5e00 00fe 0060 1d7d 0807 8100 0104
        0x0010:  0800 4500 0048 d684 0000 0111 3e1c 6405
        0x0020:  5101 ef00 00fe 9786 07e4 0034 a54a 4479

IPV6 的 tcpdump 仅显示自动生成的 IPV6 多播消息：

2020-04-02 22:48:19.569203 00:60:1d:7d:08:07 (oui Unknown) > 33:33:00:00:00:16 (oui Unknown), ethertype 802.1Q (0x8100), length 174: vlan 260, p 0, ethertype IPv6, [|ip6]
        0x0000:  3333 0000 0016 0060 1d7d 0807 8100 0104
        0x0010:  86dd 6000 0000 0074 0001 0000 0000 0000
        0x0020:  0000 0000 0000 0000 0000 ff02 0000 0000
2020-04-02 22:48:20.049156 00:60:1d:7d:08:07 (oui Unknown) > 33:33:00:00:00:16 (oui Unknown), ethertype 802.1Q (0x8100), length 174: vlan 260, p 0, ethertype IPv6, [|ip6]
        0x0000:  3333 0000 0016 0060 1d7d 0807 8100 0104
        0x0010:  86dd 6000 0000 0074 0001 0000 0000 0000
        0x0020:  0000 0000 0000 0000 0000 ff02 0000 0000
2020-04-02 22:48:20.329171 00:60:1d:7d:08:07 (oui Unknown) > 33:33:ff:7d:08:07 (oui Unknown), ethertype 802.1Q (0x8100), length 90: vlan 260, p 0, ethertype IPv6, [|ip6]
        0x0000:  3333 ff7d 0807 0060 1d7d 0807 8100 0104
        0x0010:  86dd 6000 0000 0020 3aff 0000 0000 0000
        0x0020:  0000 0000 0000 0000 0000 ff02 0000 0000
root@MEC2-81-1-STDBY:/lib# 2020-04-02 22:48:21.359289 00:60:1d:7d:08:07 (oui Unknown) > 33:33:00:00:00:16 (oui Unknown), ethertype 802.1Q (0x8100), length 134: vlan 260, p 0, ethertype IPv6, [|ip6]
        0x0000:  3333 0000 0016 0060 1d7d 0807 8100 0104
        0x0010:  86dd 6000 0000 004c 0001 fe80 0000 0000
        0x0020:  0000 0260 1dff fe7d 0807 ff02 0000 0000
2020-04-02 22:48:21.389154 00:60:1d:7d:08:07 (oui Unknown) > 33:33:00:00:00:16 (oui Unknown), ethertype 802.1Q (0x8100), length 94: vlan 260, p 0, ethertype IPv6, [|ip6]
        0x0000:  3333 0000 0016 0060 1d7d 0807 8100 0104
        0x0010:  86dd 6000 0000 0024 0001 fe80 0000 0000
        0x0020:  0000 0260 1dff fe7d 0807 ff02 0000 0000
2020-04-02 22:48:22.159152 00:60:1d:7d:08:07 (oui Unknown) > 33:33:00:00:00:16 (oui Unknown), ethertype 802.1Q (0x8100), length 134: vlan 260, p 0, ethertype IPv6, [|ip6]
        0x0000:  3333 0000 0016 0060 1d7d 0807 8100 0104
        0x0010:  86dd 6000 0000 004c 0001 fe80 0000 0000
        0x0020:  0000 0260 1dff fe7d 0807 ff02 0000 0000
2020-04-02 22:48:22.319152 00:60:1d:7d:08:07 (oui Unknown) > 33:33:00:00:00:16 (oui Unknown), ethertype 802.1Q (0x8100), length 94: vlan 260, p 0, ethertype IPv6, [|ip6]
        0x0000:  3333 0000 0016 0060 1d7d 0807 8100 0104
        0x0010:  86dd 6000 0000 0024 0001 fe80 0000 0000
        0x0020:  0000 0260 1dff fe7d 0807 ff02 0000 0000

网络接口：使用的网络接口是 VLAN ID 为 260 的 VLAN 接口 svlan1_260，在物理网络接口 eth2 上创建。

eth2      Link encap:Ethernet  HWaddr 00:00:00:00:81:01  
          UP BROADCAST RUNNING PROMISC MULTICAST  MTU:1513  Metric:1
          RX packets:3684437 errors:0 dropped:0 overruns:0 frame:0
          TX packets:3410666 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:572562185 (546.0 MiB)  TX bytes:109620349 (104.5 MiB)
          Interrupt:32
svlan1_260 Link encap:Ethernet  HWaddr 00:60:1d:7d:08:07  
          inet addr:100.5.81.1  Bcast:100.5.255.255  Mask:255.255.0.0
          inet6 addr: fe80::260:1dff:fe7d:807/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:0 errors:0 dropped:0 overruns:0 frame:0
          TX packets:709 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:0 (0.0 B)  TX bytes:85982 (83.9 KiB)

问题：

有什么想法，IPv6出了什么问题？

可能是地址不对，虽然我试了几个？

任何缺少的套接字配置？

任何系统设置，没有正确设置？

谢谢

Answer 1

经过多次调试，找到了问题的原因。

上面评论中提到的 T 位标志（动态分配的多播地址）肯定应该正确设置。 但是，如果 T 位设置为 0（众所周知的多播地址），发送也可以。

sendto 调用失败的原因如下。 在创建套接字和发送消息之前很短的时间，在相应的网络接口上，MAC 地址已通过 ioctl SIOCsIFHWADDR 更改。 为了使用新的 MAC 地址自动更新本地 IPv6 地址，网络接口通过 ioctl SIOCSIFFLAGS 重新设置和重新设置。

创建套接字并发送消息时，链接尚未完成。 因此 sendto 失败。 上面 tcpdump 中的 IPv6 消息属于网络接口启动。

在网络接口启动后等待几秒钟，一切正常。