usr/src/sys/netinet/in_var.h

/*      in_var.h        6.1     85/03/18        */

/*
 * Interface address, internet version.  One of these structures
 * is allocated for each interface with an internet address.
 * The ifaddr structure contains the protocol-independent part
 * of the structure and is assumed to be first.
 */
struct in_ifaddr {
        struct  ifaddr ia_ifa;          /* protocol-independent info */
#define ia_addr ia_ifa.ifa_addr
#define ia_broadaddr    ia_ifa.ifa_broadaddr
#define ia_dstaddr      ia_ifa.ifa_dstaddr
#define ia_ifp          ia_ifa.ifa_ifp
        u_long  ia_net;                 /* network number of interface */
        u_long  ia_netmask;             /* mask of net part */
        u_long  ia_subnet;              /* subnet number, including net */
        u_long  ia_subnetmask;          /* mask of net + subnet */
        int     ia_flags;
        struct  in_ifaddr *ia_next;     /* next in list of internet addresses */
};
/*
 * Given a pointer to an in_ifaddr (ifaddr),
 * return a pointer to the addr as a sockadd_in.
 */
#define IA_SIN(ia) ((struct sockaddr_in *)(&((struct in_ifaddr *)ia)->ia_addr))
/*
 * ia_flags
 */
#define IFA_ROUTE       0x01            /* routing entry installed */

#ifdef  KERNEL
extern  struct in_ifaddr *in_ifaddr;
extern  struct in_ifaddr *in_iaonnetof();
#endif