1 /* $OpenBSD: tcp_timer.h,v 1.3 1997/02/24 14:06:46 niklas Exp $ */ 2 /* $NetBSD: tcp_timer.h,v 1.6 1995/03/26 20:32:37 jtc Exp $ */ 3 4 /* 5 * Copyright (c) 1982, 1986, 1993 6 * The Regents of the University of California. All rights reserved. 7 * 8 * Redistribution and use in source and binary forms, with or without 9 * modification, are permitted provided that the following conditions 10 * are met: 11 * 1. Redistributions of source code must retain the above copyright 12 * notice, this list of conditions and the following disclaimer. 13 * 2. Redistributions in binary form must reproduce the above copyright 14 * notice, this list of conditions and the following disclaimer in the 15 * documentation and/or other materials provided with the distribution. 16 * 3. All advertising materials mentioning features or use of this software 17 * must display the following acknowledgement: 18 * This product includes software developed by the University of 19 * California, Berkeley and its contributors. 20 * 4. Neither the name of the University nor the names of its contributors 21 * may be used to endorse or promote products derived from this software 22 * without specific prior written permission. 23 * 24 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 25 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 26 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 27 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 28 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 29 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 30 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 31 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 32 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 33 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 34 * SUCH DAMAGE. 35 * 36 * @(#)tcp_timer.h 8.1 (Berkeley) 6/10/93 37 */ 38 39 /* 40 * Definitions of the TCP timers. These timers are counted 41 * down PR_SLOWHZ times a second. 42 */ 43 #define TCPT_NTIMERS 4 44 45 #define TCPT_REXMT 0 /* retransmit */ 46 #define TCPT_PERSIST 1 /* retransmit persistance */ 47 #define TCPT_KEEP 2 /* keep alive */ 48 #define TCPT_2MSL 3 /* 2*msl quiet time timer */ 49 50 /* 51 * The TCPT_REXMT timer is used to force retransmissions. 52 * The TCP has the TCPT_REXMT timer set whenever segments 53 * have been sent for which ACKs are expected but not yet 54 * received. If an ACK is received which advances tp->snd_una, 55 * then the retransmit timer is cleared (if there are no more 56 * outstanding segments) or reset to the base value (if there 57 * are more ACKs expected). Whenever the retransmit timer goes off, 58 * we retransmit one unacknowledged segment, and do a backoff 59 * on the retransmit timer. 60 * 61 * The TCPT_PERSIST timer is used to keep window size information 62 * flowing even if the window goes shut. If all previous transmissions 63 * have been acknowledged (so that there are no retransmissions in progress), 64 * and the window is too small to bother sending anything, then we start 65 * the TCPT_PERSIST timer. When it expires, if the window is nonzero, 66 * we go to transmit state. Otherwise, at intervals send a single byte 67 * into the peer's window to force him to update our window information. 68 * We do this at most as often as TCPT_PERSMIN time intervals, 69 * but no more frequently than the current estimate of round-trip 70 * packet time. The TCPT_PERSIST timer is cleared whenever we receive 71 * a window update from the peer. 72 * 73 * The TCPT_KEEP timer is used to keep connections alive. If an 74 * connection is idle (no segments received) for TCPTV_KEEP_INIT amount of time, 75 * but not yet established, then we drop the connection. Once the connection 76 * is established, if the connection is idle for TCPTV_KEEP_IDLE time 77 * (and keepalives have been enabled on the socket), we begin to probe 78 * the connection. We force the peer to send us a segment by sending: 79 * <SEQ=SND.UNA-1><ACK=RCV.NXT><CTL=ACK> 80 * This segment is (deliberately) outside the window, and should elicit 81 * an ack segment in response from the peer. If, despite the TCPT_KEEP 82 * initiated segments we cannot elicit a response from a peer in TCPT_MAXIDLE 83 * amount of time probing, then we drop the connection. 84 */ 85 86 /* 87 * Time constants. 88 */ 89 #define TCPTV_MSL ( 30*PR_SLOWHZ) /* max seg lifetime (hah!) */ 90 #define TCPTV_SRTTBASE 0 /* base roundtrip time; 91 if 0, no idea yet */ 92 #define TCPTV_SRTTDFLT ( 3*PR_SLOWHZ) /* assumed RTT if no info */ 93 94 #define TCPTV_PERSMIN ( 5*PR_SLOWHZ) /* retransmit persistance */ 95 #define TCPTV_PERSMAX ( 60*PR_SLOWHZ) /* maximum persist interval */ 96 97 #define TCPTV_KEEP_INIT ( 75*PR_SLOWHZ) /* initial connect keep alive */ 98 #define TCPTV_KEEP_IDLE (120*60*PR_SLOWHZ) /* dflt time before probing */ 99 #define TCPTV_KEEPINTVL ( 75*PR_SLOWHZ) /* default probe interval */ 100 #define TCPTV_KEEPCNT 8 /* max probes before drop */ 101 102 #define TCPTV_MIN ( 1*PR_SLOWHZ) /* minimum allowable value */ 103 #define TCPTV_REXMTMAX ( 64*PR_SLOWHZ) /* max allowable REXMT value */ 104 105 #define TCP_LINGERTIME 120 /* linger at most 2 minutes */ 106 107 #define TCP_MAXRXTSHIFT 12 /* maximum retransmits */ 108 109 #ifdef TCPTIMERS 110 char *tcptimers[] = 111 { "REXMT", "PERSIST", "KEEP", "2MSL" }; 112 #endif 113 114 /* 115 * Force a time value to be in a certain range. 116 */ 117 #define TCPT_RANGESET(tv, value, tvmin, tvmax) { \ 118 (tv) = (value); \ 119 if ((tv) < (tvmin)) \ 120 (tv) = (tvmin); \ 121 else if ((tv) > (tvmax)) \ 122 (tv) = (tvmax); \ 123 } 124 125 #ifdef _KERNEL 126 extern int tcptv_keep_init; 127 extern int tcp_keepidle; /* time before keepalive probes begin */ 128 extern int tcp_keepintvl; /* time between keepalive probes */ 129 extern int tcp_maxidle; /* time to drop after starting probes */ 130 extern int tcp_ttl; /* time to live for TCP segs */ 131 extern int tcp_backoff[]; 132 #endif 133