在IPv6环境中，使用UDP套接字时，`setsockopt`和`connect()`有特定行为。`connect()`指定默认发送地址，并且若`addr`为空，将绑定到`::1`。不使用`connect()`而仅使用`bind()`时，情况不同。实测显示了这些调用如何影响UDP套接字的状态。
setsockopt
ipv6 也是可以的 实测可以
SO_BINDTODEVICE
Bind this socket to a particular device like “eth0”, as specified in the passed interface name. If the name is an
empty string or the option length is zero, the socket device binding is removed. The passed option is a variable-
length null-terminated interface name string with the maximum size of IFNAMSIZ. If a socket is bound to an inter‐
face, only packets received from that particular interface are processed by the socket. Note that this works only
for some socket types, particularly AF_INET sockets. It is not supported for packet sockets (use normal bind(2)
there).
connect()
int connect(int sockfd, const struct sockaddr *addr, socklen_t addrlen);
这个东西是 UDP的话，addr 表示默认的发送地址， 但只接收这个地址的报文
如果addr 为空也就是 ::
那么 将会绑定到 ::1 这个地址
udp6 0 0 2000:bb::56:1121 ::1:1111
DESCRIPTION
The connect() system call connects the socket referred to by the file descriptor sockfd to the address specified by addr.
The addrlen argument specifies the size of addr. The format of the address in addr is determined by the address space of
the socket sockfd; see socket(2) for further details.
If the socket sockfd is of type SOCK_DGRAM then addr is the address to which datagrams are sent by default, and the only
address from which datagrams are received. If the socket is of type SOCK_STREAM or SOCK_SEQPACKET, this call attempts to
make a connection to the socket that is bound to the address specified by addr.
Generally, connection-based protocol sockets may successfully connect() only once; connectionless protocol sockets may use
connect() multiple times to change their association. Connectionless sockets may dissolve the association by connecting
to an address with the sa_family member of sockaddr set to AF_UNSPEC (supported on Linux since kernel 2.2).
实测
运行以下程序有这个状态 netstat
udp6 0 0 2000:bb::56:1121 2000:bb::58:1111 ESTABLISHED
这是使用了 connect() 系统调用的结构
如果不使用 connect() 只使用了bind()
udp 0 0 3000::1:1121 :::*
#include <stdio.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <string.h>
#include <arpa/inet.h>
#include <error.h>
#include <errno.h>
#include <unistd.h>
#define ERROR_DO printf("function: %s; line NO.: %d \
error: %s \n", __FUNCTION__, __LINE__, strerror(errno))
#define PEERADDRSTR "2000:bb::58"
#define LOCLADDRSTR "2000:bb::56"
#define CONNECT_TEST
int start(int *serv_sock, int enable_connect)
{
struct sockaddr_in6 local;
struct sockaddr_in6 peer;
int ret = 0;
int local_len = 0;
int peer_len = 0;
struct in6_addr localaddr;
struct in6_addr peeraddr;
local_len = sizeof(struct sockaddr_in6);
peer_len = local_len;
memset(&local, 0, local_len);
memset(&peer, 0, peer_len);
local.sin6_family = AF_INET6;
peer.sin6_family = AF_INET6;
inet_pton(AF_INET6, PEERADDRSTR, &peeraddr);
inet_pton(AF_INET6, LOCLADDRSTR, &localaddr);
local.sin6_addr = localaddr ;
/* if not assign peeraddr that *connect() system call will set peer to ::1
udp6 0 0 2000:bb::56:1121 ::1:1111
really did
use start(, enable) connet call enable
use `netstat -natu to see the netstat`
*/
#ifndef CONNECT_TEST // not compile this line
peer.sin6_addr = peeraddr ;
#endif
local.sin6_port = htons(1121);
peer.sin6_port = htons(1111);
*serv_sock = socket(AF_INET6, SOCK_DGRAM, 0);
if(*serv_sock < 0){
ERROR_DO;
printf("[HA UDP] sock init failed.error: %s\n", strerror(errno));
return -1;
}
/* set timeout */
struct timeval tv_out;
tv_out.tv_sec = 5;
tv_out.tv_usec = 0;
if(setsockopt(*serv_sock, SOL_SOCKET, SO_RCVTIMEO, &tv_out, sizeof(tv_out)) < 0){
close(*serv_sock);
ERROR_DO;
return -1;
}
if(setsockopt(*serv_sock, SOL_SOCKET, SO_BINDTODEVICE, "enp4s0", strlen("enp4s0")+1) < 0){
ERROR_DO;
printf ("******please run with sudo or as root********\n");
close(*serv_sock);
exit(0);
}
int on = 1;
if(setsockopt(*serv_sock, SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0){
close(*serv_sock);
ERROR_DO;
return -1;
}
int recv_buf = 10000000;
if(setsockopt(*serv_sock, SOL_SOCKET, SO_RCVBUF, (char *) &recv_buf, sizeof(recv_buf))< 0){
close(*serv_sock);
ERROR_DO;
return -1;
}
ret = bind(*serv_sock, (struct sockaddr *)&local, local_len);
if(ret < 0){
close(*serv_sock);
ERROR_DO;
return -1;
}
if (enable_connect) {
printf("enable udp connect\n");
ret = connect(*serv_sock, (struct sockaddr *)&peer, local_len);
if(ret < 0){
return -1;
}
}
return 0;
}
int send6(void)
{
int client_fd;
struct sockaddr_in6 ser_addr;
struct sockaddr_in6 cli_addr;
struct in6_addr seraddr;
struct in6_addr cliaddr;
#define BUFF_LEN 20
char buf[20] = {"abc"};
client_fd = socket(AF_INET6, SOCK_DGRAM, 0);
if(client_fd < 0)
{
ERROR_DO;
return -1;
}
memset(&ser_addr, 0, sizeof(ser_addr));
memset(&cli_addr, 0, sizeof(ser_addr));
inet_pton(AF_INET6, LOCLADDRSTR, &seraddr);
inet_pton(AF_INET6, PEERADDRSTR, &cliaddr);
ser_addr.sin6_family = AF_INET6;
ser_addr.sin6_addr = seraddr;
ser_addr.sin6_port = htons(1121);
cli_addr.sin6_family = AF_INET6;
cli_addr.sin6_addr = cliaddr;
cli_addr.sin6_port = htons(1111);
if (bind(client_fd, (struct sockaddr *)&cli_addr, sizeof(cli_addr)))
ERROR_DO;
sendto(client_fd, buf, BUFF_LEN, 0, (struct sockaddr*) &ser_addr, sizeof(ser_addr));
close(client_fd);
return 0;
}
int main(int argc, char **argv)
{
enum {
DISABLE_CONNECT,
ENABLE_CONNECT
};
int sock;
int len;
char buff[256] = {0};
#ifdef CONNECT_TEST
start(&sock, ENABLE_CONNECT);
#else
start(&sock, DISABLE_CONNECT);
#endif
while (1) {
// no work very well
send6();
len = read(sock, buff, 256);
if (len < 0)ERROR_DO;
printf("len: %d %s\n", len, buff);
sleep(3);
}
return 1;
}
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