1 /*
2  * Copyright (c) 1982, 1986 Regents of the University of California.
3  * All rights reserved.
4  * Copyright (c) 2016 by Delphix. All rights reserved.
5  *
6  * Redistribution and use in source and binary forms are permitted
7  * provided that the above copyright notice and this paragraph are
8  * duplicated in all such forms and that any documentation,
9  * advertising materials, and other materials related to such
10  * distribution and use acknowledge that the software was developed
11  * by the University of California, Berkeley.  The name of the
12  * University may not be used to endorse or promote products derived
13  * from this software without specific prior written permission.
14  */
15 
16 /*
17  * Definitions of the TCP timers.  These timers are counted
18  * down PR_SLOWHZ times a second.
19  */
20 
21 #ifndef	_NETINET_TCP_TIMER_H
22 #define	_NETINET_TCP_TIMER_H
23 
24 #pragma ident	"%Z%%M%	%I%	%E% SMI"
25 /* tcp_timer.h 1.13 89/06/16 SMI; from UCB 7.6 6/29/88 */
26 
27 #ifdef	__cplusplus
28 extern "C" {
29 #endif
30 
31 #define	TCPT_NTIMERS	4
32 
33 #define	TCPT_REXMT	0		/* retransmit */
34 #define	TCPT_PERSIST	1		/* retransmit persistance */
35 #define	TCPT_KEEP	2		/* keep alive */
36 #define	TCPT_2MSL	3		/* 2*msl quiet time timer */
37 
38 /*
39  * The TCPT_REXMT timer is used to force retransmissions.
40  * The TCP has the TCPT_REXMT timer set whenever segments
41  * have been sent for which ACKs are expected but not yet
42  * received.  If an ACK is received which advances tp->snd_una,
43  * then the retransmit timer is cleared (if there are no more
44  * outstanding segments) or reset to the base value (if there
45  * are more ACKs expected).  Whenever the retransmit timer goes off,
46  * we retransmit one unacknowledged segment, and do a backoff
47  * on the retransmit timer.
48  *
49  * The TCPT_PERSIST timer is used to keep window size information
50  * flowing even if the window goes shut.  If all previous transmissions
51  * have been acknowledged (so that there are no retransmissions in progress),
52  * and the window is too small to bother sending anything, then we start
53  * the TCPT_PERSIST timer.  When it expires, if the window is nonzero,
54  * we go to transmit state.  Otherwise, at intervals send a single byte
55  * into the peer's window to force it to update our window information.
56  * We do this at most as often as TCPT_PERSMIN time intervals,
57  * but no more frequently than the current estimate of round-trip
58  * packet time.  The TCPT_PERSIST timer is cleared whenever we receive
59  * a window update from the peer.
60  *
61  * The TCPT_KEEP timer is used to keep connections alive.  If a
62  * connection is idle (no segments received) for TCPTV_KEEP_INIT amount of time,
63  * but not yet established, then we drop the connection.  Once the connection
64  * is established, if the connection is idle for TCPTV_KEEP_IDLE time
65  * (and keepalives have been enabled on the socket), we begin to probe
66  * the connection.  We force the peer to send us a segment by sending:
67  *	<SEQ=SND.UNA-1><ACK=RCV.NXT><CTL=ACK>
68  * This segment is (deliberately) outside the window, and should elicit
69  * an ack segment in response from the peer.  If, despite the TCPT_KEEP
70  * initiated segments we cannot elicit a response from a peer in TCPT_MAXIDLE
71  * amount of time probing, then we drop the connection.
72  */
73 
74 #define	TCP_TTL		60		/* default time to live for TCP segs */
75 /*
76  * Time constants.
77  */
78 #define	TCPTV_MSL	(30*PR_SLOWHZ)		/* max seg lifetime (hah!) */
79 #define	TCPTV_SRTTBASE	0			/* base roundtrip time; */
80 						/* if 0, no idea yet */
81 #define	TCPTV_SRTTDFLT	(3*PR_SLOWHZ)		/* assumed RTT if no info */
82 
83 #define	TCPTV_PERSMIN	(5*PR_SLOWHZ)		/* retransmit persistance */
84 #define	TCPTV_PERSMAX	(60*PR_SLOWHZ)		/* maximum persist interval */
85 
86 #define	TCPTV_KEEP_INIT	(75*PR_SLOWHZ)		/* initial connect keep alive */
87 #define	TCPTV_KEEP_IDLE	(120*60*PR_SLOWHZ)	/* dflt time before probing */
88 #define	TCPTV_KEEPINTVL	(75*PR_SLOWHZ)		/* default probe interval */
89 #define	TCPTV_KEEPCNT	8			/* max probes before drop */
90 
91 #define	TCPTV_MIN	(1*PR_SLOWHZ)		/* minimum allowable value */
92 #define	TCPTV_REXMTMAX	(64*PR_SLOWHZ)		/* max allowable REXMT value */
93 
94 #define	TCP_LINGERTIME	120			/* linger at most 2 minutes */
95 
96 #define	TCP_MAXRXTSHIFT	12			/* maximum retransmits */
97 
98 #ifdef	TCPTIMERS
99 char *tcptimers[] =
100 	{ "REXMT", "PERSIST", "KEEP", "2MSL" };
101 #endif
102 
103 /*
104  * Force a time value to be in a certain range.
105  */
106 #define	TCPT_RANGESET(tv, value, tvmin, tvmax) { \
107 	(tv) = (value); \
108 	if ((tv) < (tvmin)) \
109 		(tv) = (tvmin); \
110 	else if ((tv) > (tvmax)) \
111 		(tv) = (tvmax); \
112 }
113 
114 #ifdef	__cplusplus
115 }
116 #endif
117 
118 #endif	/* _NETINET_TCP_TIMER_H */
119