即使将SO_REUSEADDR与IPv6一起使用，套接字绑定也会失败 [英] Socket bind fails even after using SO_REUSEADDR with IPv6

问题描述

我的应用程序需要在具有相同IPv6地址的同一端口上绑定套接字.我正在使用下面的代码来实现相同的目的.但是，第二个绑定会引发错误地址已在使用中". 顺便说一句，只有当我包含第一个套接字的监听调用时，我才会收到此错误.没有监听调用，第二个套接字绑定就可以了.

My application needs to bind a socket on the same port with the same IPv6 address. I am using the code below to achieve the same. However second bind throws an error 'Address already in use'. BTW, i get this error only if I include the listen call for the first socket. Without the listen call, the second socket binds just fine.

我做错了什么?请帮助我理解.

What I am doing wrong? Please help me understand.

谢谢

int fd1 = ::socket(AF_INET6, SOCK_STREAM, 0);
if (fd1 < 0)
{
    perror("fd1 socket()");
    return -1;
}

// Set SO_REUSEADDR for both sockets
int reuse = 1;
if (fcntl(fd1, F_SETFL, O_RDWR|O_NONBLOCK) <0)
{
    perror("fd1 fcntl64 failed");
    return -1;
}
if (::setsockopt(fd1, SOL_SOCKET, SO_REUSEADDR, &reuse, sizeof(reuse)) < 0)
{
    perror("fd1 SO_REUSEADDR failed");
    return -1;
}
if (::setsockopt(fd1, SOL_IPV6, IPV6_V6ONLY, &reuse, sizeof(reuse)) < 0)
{
    perror("fd1 SO_REUSEADDR failed");
    return -1;
}


sockaddr_storage storage;
socklen_t addrlen = sizeof(storage);
memset(&storage, 0, addrlen);
sockaddr_in6& addr = reinterpret_cast<sockaddr_in6&>(storage);
addr.sin6_family = AF_INET6;
addr.sin6_port = 143;
addr.sin6_addr = in6addr_any;
sockaddr* pAddr = reinterpret_cast<sockaddr*>(&storage);

int val = 2;
socklen_t len = sizeof(val);

if (::getsockopt(fd1, SOL_SOCKET, SO_REUSEADDR, &val, &len) < 0)
{
    perror("fd1 getsock failed");
    return -1;
}

printf("Getsockopt returned %d at %d\n",val, __LINE__);

if (::bind(fd1, pAddr, sizeof(sockaddr_in6)) < 0)
{
    perror("bind fd1 failed");
    return -1;
}

if (::getsockopt(fd1, SOL_SOCKET, SO_REUSEADDR, &val, &len) < 0)
{
    perror("fd1 getsock failed");
    return -1;
}

printf("Getsockopt returned %d at %d\n",val, __LINE__);
if (listen(fd1, 128) < 0)
{
    perror("fd1, listen");
        return -1;
}
if (::getsockopt(fd1, SOL_SOCKET, SO_REUSEADDR, &val, &len) < 0)
{
    perror("fd1 getsock failed");
    return -1;
}

printf("Getsockopt returned %d at %d\n",val, __LINE__);
// Get the local address for fd1
addrlen = sizeof(storage);
if (::getsockname(fd1, pAddr, &addrlen))
{
    perror("getsockname for fd1 failed");
    return -1;
}
char straddr[INET6_ADDRSTRLEN];
if (!inet_ntop(AF_INET6, &addr.sin6_addr, straddr, sizeof(straddr)))
{
    perror("inet_ntop for fd1 failed");
    return -1;
}
printf("fd1=%d addr=%s:%d\n", fd1, straddr, addr.sin6_port);

addrlen = sizeof(storage);
addr.sin6_family = AF_INET6;
addr.sin6_port = 143;
int fd2 = ::socket(AF_INET6, SOCK_STREAM, 0);
if (fd2 < 0)
{
    perror("fd2 socket()");
    return -1;
}
if (::setsockopt(fd2, SOL_SOCKET, SO_REUSEADDR, &reuse, sizeof(reuse)) < 0)
{
    perror("fd2 SO_REUSEADDR failed");
    return -1;
}
if (::setsockopt(fd2, SOL_IPV6, IPV6_V6ONLY, &reuse, sizeof(reuse)) < 0)
{
    perror("fd1 SO_REUSEADDR failed");
    return -1;
}

if (::bind(fd2, pAddr, sizeof(sockaddr_in6)) < 0)
{
    perror("bind fd2 failed");
    return -1;
}

// Get the local address for fd2
if (::getsockname(fd2, pAddr, &addrlen))
{
    perror("getsockname for fd2 failed");
    return -1;
}
if (!inet_ntop(AF_INET6, &addr.sin6_addr, straddr, sizeof(straddr)))
{
    perror("inet_ntop for fd2 failed");
    return -1;
}
printf("fd2=%d addr=%s:%d\n", fd2, straddr, addr.sin6_port);

return 0;

推荐答案

在socket(7)手册页中:

SO_REUSEADDR-指示用于验证bind(2)调用中提供的地址的规则应允许重用本地地址.对于AF_INET套接字，这意味着套接字可以绑定，除外，除非有活动的监听套接字绑定到该地址.当侦听套接字使用特定端口绑定到INADDR_ANY时，则不可能将其绑定到任何本地地址.参数是一个整数布尔值标志.

SO_REUSEADDR - Indicates that the rules used in validating addresses supplied in a bind(2) call should allow reuse of local addresses. For AF_INET sockets this means that a socket may bind, except when there is an active listening socket bound to the address. When the listening socket is bound to INADDR_ANY with a specific port then it is not possible to bind to this port for any local address. Argument is an integer boolean flag.

(重点是我的)

您的第一个套接字绑定到与INADDR_ANY等效的IPv6上的端口143，然后进入侦听状态.因此，只要第一个插座保持打开状态，端口143上就不会绑定其他插座.

Your first socket is bound to port 143 on the IPv6 equivalent of INADDR_ANY, then it's put in listening state. Thus no other socket could be bound on port 143 as long as the first socket remains open.

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