usr/src/sys/netinet/tcp.h

/*
 * Copyright (c) 1982, 1986 Regents of the University of California.
 * All rights reserved.
 *
 * %sccs.include.redist.c%
 *
 *      @(#)tcp.h       7.7 (Berkeley) %G%
 */
#ifndef BYTE_ORDER
/*
 * Definitions for byte order,
 * according to byte significance from low address to high.
 */
#define LITTLE_ENDIAN   1234    /* least-significant byte first (vax) */
#define BIG_ENDIAN      4321    /* most-significant byte first (IBM, net) */
#define PDP_ENDIAN      3412    /* LSB first in word, MSW first in long (pdp) */

#ifdef vax
#define BYTE_ORDER      LITTLE_ENDIAN
#else
#define BYTE_ORDER      BIG_ENDIAN      /* mc68000, tahoe, most others */
#endif
#endif BYTE_ORDER

typedef u_long  tcp_seq;
/*
 * TCP header.
 * Per RFC 793, September, 1981.
 */
struct tcphdr {
        u_short th_sport;               /* source port */
        u_short th_dport;               /* destination port */
        tcp_seq th_seq;                 /* sequence number */
        tcp_seq th_ack;                 /* acknowledgement number */
#if BYTE_ORDER == LITTLE_ENDIAN
        u_char  th_x2:4,                /* (unused) */
                th_off:4;               /* data offset */
#endif
#if BYTE_ORDER == BIG_ENDIAN
        u_char  th_off:4,               /* data offset */
                th_x2:4;                /* (unused) */
#endif
        u_char  th_flags;
#define TH_FIN  0x01
#define TH_SYN  0x02
#define TH_RST  0x04
#define TH_PUSH 0x08
#define TH_ACK  0x10
#define TH_URG  0x20
        u_short th_win;                 /* window */
        u_short th_sum;                 /* checksum */
        u_short th_urp;                 /* urgent pointer */
};

#define TCPOPT_EOL      0
#define TCPOPT_NOP      1
#define TCPOPT_MAXSEG   2

/*
 * Default maximum segment size for TCP.
 * With an IP MSS of 576, this is 536,
 * but 512 is probably more convenient.
 * This should be defined as MIN(512, IP_MSS - sizeof (struct tcpiphdr)).
 */
#define TCP_MSS 512

#define TCP_MAXWIN      65535           /* largest value for window */

/*
 * User-settable options (used with setsockopt).
 */
#define TCP_NODELAY     0x01    /* don't delay send to coalesce packets */
#define TCP_MAXSEG      0x02    /* set maximum segment size */