usr/src/sys/netinet/ip_var.h

/*      ip_var.h        6.1     83/07/29        */

/*
 * Overlay for ip header used by other protocols (tcp, udp).
 */
struct ipovly {
        caddr_t ih_next, ih_prev;       /* for protocol sequence q's */
        u_char  ih_x1;                  /* (unused) */
        u_char  ih_pr;                  /* protocol */
        short   ih_len;                 /* protocol length */
        struct  in_addr ih_src;         /* source internet address */
        struct  in_addr ih_dst;         /* destination internet address */
};

/*
 * Ip reassembly queue structure.  Each fragment
 * being reassembled is attached to one of these structures.
 * They are timed out after ipq_ttl drops to 0, and may also
 * be reclaimed if memory becomes tight.
 */
struct ipq {
        struct  ipq *next,*prev;        /* to other reass headers */
        u_char  ipq_ttl;                /* time for reass q to live */
        u_char  ipq_p;                  /* protocol of this fragment */
        u_short ipq_id;                 /* sequence id for reassembly */
        struct  ipasfrag *ipq_next,*ipq_prev;
                                        /* to ip headers of fragments */
        struct  in_addr ipq_src,ipq_dst;
};

/*
 * Ip header, when holding a fragment.
 *
 * Note: ipf_next must be at same offset as ipq_next above
 */
struct  ipasfrag {
#ifdef vax
        u_char  ip_hl:4,
                ip_v:4;
#endif
        u_char  ipf_mff;                /* copied from (ip_off&IP_MF) */
        short   ip_len;
        u_short ip_id;
        short   ip_off;
        u_char  ip_ttl;
        u_char  ip_p;
        u_short ip_sum;
        struct  ipasfrag *ipf_next;     /* next fragment */
        struct  ipasfrag *ipf_prev;     /* previous fragment */
};

struct  ipstat {
        int     ips_badsum;             /* checksum bad */
        int     ips_tooshort;           /* packet too short */
        int     ips_toosmall;           /* not enough data */
        int     ips_badhlen;            /* ip header length < data size */
        int     ips_badlen;             /* ip length < ip header length */
};

#ifdef KERNEL
/* flags passed to ip_output as last parameter */
#define IP_FORWARDING           0x1     /* most of ip header exists */
#define IP_ROUTETOIF            0x10    /* same as SO_DONTROUTE */
#define IP_ALLOWBROADCAST       SS_PRIV /* can send broadcast packets */

struct  ipstat  ipstat;
struct  ipq     ipq;                    /* ip reass. queue */
u_short ip_id;                          /* ip packet ctr, for ids */
#endif