使用IN6ADDR_SETV4MAPPED和双堆栈套接字

Question

这是Connecting IPv4 client to IPv6 server: connection refused的延续。我正在尝试使用双堆栈套接字，并试图了解使用IPV6_V6ONLY的setsockopt有什么用处。在链接的问题上，我被建议“如果您还将服务器绑定到IPV6映射的IPv4地址，则将IPV6_V6ONLY设置为0会很有用”。我已经在下面这样做了，并且期望我的服务器能够接受来自IPv6和IPv4客户机的连接。但令人震惊的是，当我使用V4和V6套接字运行客户机时，两者都无法连接！

有人能告诉我我做错了什么吗，或者我误解了IPv6双栈功能？

服务器：

void ConvertToV4MappedAddressIfNeeded(PSOCKADDR pAddr)
{
// if v4 address, convert to v4 mapped v6 address
if (AF_INET == pAddr->sa_family)
{
    IN_ADDR In4addr;
    SCOPE_ID scope = INETADDR_SCOPE_ID(pAddr);
    USHORT port = INETADDR_PORT(pAddr);
    In4addr = *(IN_ADDR*)INETADDR_ADDRESS(pAddr);
    ZeroMemory(pAddr, sizeof(SOCKADDR_STORAGE));
    IN6ADDR_SETV4MAPPED(
        (PSOCKADDR_IN6)pAddr,
        &In4addr,
        scope,
        port
        );
    }
} 

addrinfo* result, hints;

memset(&hints, 0, sizeof hints); 
hints.ai_family = AF_INET;
hints.ai_socktype = SOCK_STREAM;
hints.ai_flags = AI_PASSIVE;

int nRet = getaddrinfo("powerhouse", "82", &hints, &result);

SOCKET sock = socket(AF_INET6, SOCK_STREAM, IPPROTO_TCP);

int no = 0;
if (setsockopt(sock, IPPROTO_IPV6, IPV6_V6ONLY, (char*)&no, sizeof(no)) != 0)
    return -1;

ConvertToV4MappedAddressIfNeeded(result->ai_addr);

if (bind(sock, result->ai_addr, 28/*result->ai_addrlen*/) ==  SOCKET_ERROR)
    return -1;

if (listen(sock, SOMAXCONN) == SOCKET_ERROR)
    return -1;

SOCKET sockClient = accept(sock, NULL, NULL);
printf("Got one!\n");

客户端：

addrinfo* result, *pCurrent, hints;
char szIPAddress[INET6_ADDRSTRLEN];

memset(&hints, 0, sizeof hints);    // Must do this!
hints.ai_family = AF_INET;
hints.ai_socktype = SOCK_STREAM;

const char* pszPort = "82";

if (getaddrinfo("powerhouse", "82", &hints, &result) != 0)
    return -1;

SOCKET sock = socket(AF_INET, result->ai_socktype, result->ai_protocol);
int nRet = connect(sock, result->ai_addr, result->ai_addrlen);  

Answer 1

我的C语言技能有点生疏，所以这里有一个用Python编写的反例。我的本地IPv4地址是37.77.56.75，所以我将绑定到这个地址。我尽可能地保持简单，专注于概念。

这是服务器端：

#!/usr/bin/env python
import socket

# We bind to an IPv6 address, which contains an IPv6-mapped-IPv4-address,
# port 5000 and we leave the flowinfo (an ID that identifies a flow, not used
# a lot) and the scope-id (basically the interface, necessary if using
# link-local addresses)
host = '::ffff:37.77.56.75'
port = 5000
flowinfo = 0
scopeid = 0
sockaddr = (host, port, flowinfo, scopeid)

# Create an IPv6 socket, set IPV6_V6ONLY=0 and bind to the mapped address
sock = socket.socket(socket.AF_INET6, socket.SOCK_STREAM, 0)
sock.setsockopt(socket.IPPROTO_IPV6, socket.IPV6_V6ONLY, 0)
sock.bind(sockaddr)

# Listen and accept a connection
sock.listen(0)
conn = sock.accept()

# Print the remote address
print conn[1]

在这里，我们在代码中绑定到一个IPv6地址，但该地址实际上是一个映射到ipv6的IPv4地址，因此实际上我们绑定到一个IPv4地址。这可以在查看netstat时看到：

$ netstat -an | fgrep 5000
tcp4       0      0  37.77.56.75.5000       *.*                    LISTEN     

然后，我们可以使用IPv4客户端连接到此服务器：

#!/usr/bin/env python
import socket

# Connect to an IPv4 address on port 5000
host = '37.77.56.75'
port = 5000
sockaddr = (host, port)                   

# Create an IPv4 socket and connect
sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM, 0) 
conn = sock.connect(sockaddr)

服务器将使用IPv6地址表示向我们显示是谁连接的：

('::ffff:37.77.56.76', 50887, 0, 0)

在本例中，我从IPv4主机37.77.56.76连接，它选择端口50887进行连接。

在本例中，我们只监听一个IPv4地址(使用IPv6套接字，但它仍然是一个IPv4地址)，因此仅限IPV6的客户端将无法连接。同时具有IPv4和IPv6的客户端当然可以使用具有IPv6映射的IPv4地址的IPv6套接字，但这样它就不会真正使用IPv6，而只是IPv4连接的IPv6表示。

双堆栈服务器必须满足以下任一条件：

1. 侦听通配符地址，这将使操作系统接受任何地址( IPv4和IPv6 )上的连接
2. 侦听IPv6地址和IPv4地址(通过创建IPv4套接字，或通过创建IPv6套接字并侦听ipv6映射的ipv4地址，如上所述)

使用通配符地址是最简单的。只需使用上面的服务器示例并替换主机名：

# We bind to the wildcard IPv6 address, which will make the OS listen on both
# IPv4 and IPv6
host = '::'
port = 5000
flowinfo = 0
scopeid = 0
sockaddr = (host, port, flowinfo, scopeid)

我的Mac OS X框显示为：

$ netstat -an | fgrep 5000
tcp46      0      0  *.5000                 *.*                    LISTEN     

请注意tcp46，它表示侦听两个地址族。不幸的是，在Linux上，它只显示tcp6，即使同时监听两个系列。

现在是最复杂的例子:监听多个套接字。

#!/usr/bin/env python
import select
import socket

# We bind to an IPv6 address, which contains an IPv6-mapped-IPv4-address
sockaddr1 = ('::ffff:37.77.56.75', 5001, 0, 0)

sock1 = socket.socket(socket.AF_INET6, socket.SOCK_STREAM, 0)
sock1.setsockopt(socket.IPPROTO_IPV6, socket.IPV6_V6ONLY, 0)
sock1.bind(sockaddr1)
sock1.listen(0)

# And we bind to a real IPv6 address
sockaddr2 = ('2a00:8640:1::224:36ff:feef:1d89', 5001, 0, 0)

sock2 = socket.socket(socket.AF_INET6, socket.SOCK_STREAM, 0)
sock2.bind(sockaddr2)
sock2.listen(0)

# Select sockets that become active
sockets = [sock1, sock2]
readable, writable, exceptional = select.select(sockets, [], sockets)
for sock in readable:
    # Accept the connection
    conn = sock.accept()

    # Print the remote address
    print conn[1]

运行此示例时，两个套接字都可见：

$ netstat -an | fgrep 5000
tcp6       0      0  2a00:8640:1::224.5000  *.*                    LISTEN     
tcp4       0      0  37.77.56.75.5000       *.*                    LISTEN     

现在，只有ipv6的客户端可以连接到2a00:8640:1::224:36ff:feef:1d89，而ipv4的客户端可以连接到37.77.56.75。双堆栈客户端可以选择要使用的协议。