几个重要的网络结构体

/* Interface request structure used for socket ioctl's. All interface
ioctl's must have parameter definitions which begin with ifr_name.
The remainder may be interface specific. */
struct　ifreq
{
#ifndef IFNAMSIZ
#define IFNAMSIZ　　　　16
#endif
char　　ifr_name[IFNAMSIZ];
union {
struct　sockaddr ifru_addr;
struct　sockaddr ifru_dstaddr;
struct　sockaddr ifru_broadaddr;
__ulong32_t ifru_flags;
int　　 ifru_metric;
CADdr_t ifru_data;
u_short ifru_site6;
__ulong32_t　 ifru_mtu;
int　　 ifru_baudrate;
} ifr_ifru;
//Following Macros are provided for convenIEnce
#define ifr_addr　　　　ifr_ifru.ifru_addr　　　/* address */
#define ifr_dstaddr ifr_ifru.ifru_dstaddr　 /* other end of p-to-p link */
#define ifr_broadaddr ifr_ifru.ifru_broadaddr /* broadcast address */
#define ifr_flags ifr_ifru.ifru_flags　　 /* flags */
#define ifr_metric　　　ifr_ifru.ifru_metric　　/* metric */
#define ifr_data　　　　ifr_ifru.ifru_data　　　/* for use by interface */
#define ifr_site6 ifr_ifru.ifru_site6　　 /* IPv6 site index */
#define ifr_mtu ifr_ifru.ifru_mtu　　　 /* mtu of interface */
#define ifr_isno　　　　ifr_ifru.ifru_data　　　/* pointer to if_netopts */
#define ifr_baudrate　　ifr_ifru.ifru_baudrate　/* baudrate of interface */
};
/* Structure used in SIOCGIFCONF request. Used to retrieve interface
configuration for machine (useful for programs which must know all
networks accessible). */
struct　ifconf
{
int　　 ifc_len;　　　　　　　　/* size of associated buffer */
union
{
caddr_t ifcu_buf;
struct　ifreq *ifcu_req;
} ifc_ifcu;
Following macros are provided for convenience
#define ifc_buf ifc_ifcu.ifcu_buf　　　 /* buffer address */
#define ifc_req ifc_ifcu.ifcu_req　　　 /* array of structures returned */
};
SIOCGIFADDR：获取接口地址，检索特定接口的地址
SIOCSIFADDR：设置接口地址。ifr.ifr_addr 字段返回地址。
SIOCGIFCONF：获取所有配置接口的信息，返回系统中配置的所有接口的配置信息
以上介绍转自：http://hi.baidu.com/leezongfanblog/blog/item/a86a564583934a88b3b7dc0e.html
struct sockaddr
{
unsigned short sa_family; /* 地址族, AF_xxx */
char sa_data[14]; /* 14字节的协议地址*/
};
typedef void *caddr_t;