ipヘッダ指定して接続の可、不可を判定できる関数は無いんだろか
connectだとヘッダ指定上手くいかね
#include <string.h>
#include <winsock.h>

struct ip_header {
unsigned char ip_ihl:4; /* header length */
unsigned char ip_v:4; /* version */
unsigned char ip_tos; /* type of service */
unsigned short ip_len; /* total length */
unsigned short ip_id; /* identification */
unsigned short ip_off; /* fragment offset field */
unsigned char ip_ttl; /* time to live (TTL) */
unsigned char ip_p; /* protocol */
unsigned short ip_sum; /* header checksum */
struct in_addr ip_src; /* source ip address */
struct in_addr ip_dst; /* destination ip address */
struct ip_option ip_opt; /* option */
};

struct ip {
struct ip_header iph;
char data[65500];
};