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31 * @(#)tcp_timer.h 8.1 (Berkeley) 6/10/93
35 #ifndef _NETINET_TCP_TIMER_H_
36 #define _NETINET_TCP_TIMER_H_
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.
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 him 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.
61 * The TCPT_KEEP timer is used to keep connections alive. If an
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.
77 #define TCPTV_MSL ( 30*hz) /* max seg lifetime (hah!) */
78 #define TCPTV_SRTTBASE 0 /* base roundtrip time;
80 #define TCPTV_RTOBASE ( 1*hz) /* assumed RTO if no info */
82 #define TCPTV_PERSMIN ( 5*hz) /* minimum persist interval */
83 #define TCPTV_PERSMAX ( 60*hz) /* maximum persist interval */
85 #define TCPTV_KEEP_INIT ( 75*hz) /* initial connect keepalive */
86 #define TCPTV_KEEP_IDLE (120*60*hz) /* dflt time before probing */
87 #define TCPTV_KEEPINTVL ( 75*hz) /* default probe interval */
88 #define TCPTV_KEEPCNT 8 /* max probes before drop */
90 #define TCPTV_FINWAIT2_TIMEOUT (60*hz) /* FIN_WAIT_2 timeout if no receiver */
93 * Minimum retransmit timer is 3 ticks, for algorithmic stability.
94 * TCPT_RANGESET() will add another TCPTV_CPU_VAR to deal with
95 * the expected worst-case processing variances by the kernels
96 * representing the end points. Such variances do not always show
97 * up in the srtt because the timestamp is often calculated at
98 * the interface rather then at the TCP layer. This value is
99 * typically 50ms. However, it is also possible that delayed
100 * acks (typically 100ms) could create issues so we set the slop
101 * to 200ms to try to cover it. Note that, properly speaking,
102 * delayed-acks should not create a major issue for interactive
103 * environments which 'P'ush the last segment, at least as
104 * long as implementations do the required 'at least one ack
105 * for every two packets' for the non-interactive streaming case.
106 * (maybe the RTO calculation should use 2*RTT instead of RTT
107 * to handle the ack-every-other-packet case).
109 * The prior minimum of 1*hz (1 second) badly breaks throughput on any
110 * networks faster then a modem that has minor (e.g. 1%) packet loss.
112 #define TCPTV_MIN ( hz/33 ) /* minimum allowable value */
113 #define TCPTV_CPU_VAR ( hz/5 ) /* cpu variance allowed (200ms) */
114 #define TCPTV_REXMTMAX ( 64*hz) /* max allowable REXMT value */
116 #define TCPTV_TWTRUNC 8 /* RTO factor to truncate TW */
118 #define TCP_LINGERTIME 120 /* linger at most 2 minutes */
120 #define TCP_MAXRXTSHIFT 12 /* maximum retransmits */
122 #define TCPTV_DELACK ( hz/10 ) /* 100ms timeout */
125 * If we exceed this number of retransmits for a single segment, we'll consider
126 * the current srtt measurement no longer valid and will recalculate from
127 * scratch starting with the next ACK.
129 #define TCP_RTT_INVALIDATE (TCP_MAXRXTSHIFT / 4)
132 static const char *tcptimers[] =
133 { "REXMT", "PERSIST", "KEEP", "2MSL", "DELACK" };
137 * Force a time value to be in a certain range.
139 #define TCPT_RANGESET(tv, value, tvmin, tvmax) do { \
140 (tv) = (value) + tcp_rexmit_slop; \
141 if ((u_long)(tv) < (u_long)(tvmin)) \
143 if ((u_long)(tv) > (u_long)(tvmax)) \
152 struct callout tt_rexmt; /* retransmit timer */
153 struct callout tt_persist; /* retransmit persistence */
154 struct callout tt_keep; /* keepalive */
155 struct callout tt_2msl; /* 2*msl TIME_WAIT timer */
156 struct callout tt_delack; /* delayed ACK timer */
157 uint32_t tt_flags; /* Timers flags */
158 uint32_t tt_draincnt; /* Count being drained */
162 * Flags for the tt_flags field.
164 #define TT_DELACK 0x0001
165 #define TT_REXMT 0x0002
166 #define TT_PERSIST 0x0004
167 #define TT_KEEP 0x0008
168 #define TT_2MSL 0x0010
169 #define TT_MASK (TT_DELACK|TT_REXMT|TT_PERSIST|TT_KEEP|TT_2MSL)
172 * Suspend flags - used when suspending a timer
173 * from ever running again.
175 #define TT_DELACK_SUS 0x0100
176 #define TT_REXMT_SUS 0x0200
177 #define TT_PERSIST_SUS 0x0400
178 #define TT_KEEP_SUS 0x0800
179 #define TT_2MSL_SUS 0x1000
181 #define TT_STOPPED 0x00010000
183 #define TP_KEEPINIT(tp) ((tp)->t_keepinit ? (tp)->t_keepinit : tcp_keepinit)
184 #define TP_KEEPIDLE(tp) ((tp)->t_keepidle ? (tp)->t_keepidle : tcp_keepidle)
185 #define TP_KEEPINTVL(tp) ((tp)->t_keepintvl ? (tp)->t_keepintvl : tcp_keepintvl)
186 #define TP_KEEPCNT(tp) ((tp)->t_keepcnt ? (tp)->t_keepcnt : tcp_keepcnt)
187 #define TP_MAXIDLE(tp) (TP_KEEPCNT(tp) * TP_KEEPINTVL(tp))
189 extern int tcp_persmin; /* minimum persist interval */
190 extern int tcp_persmax; /* maximum persist interval */
191 extern int tcp_keepinit; /* time to establish connection */
192 extern int tcp_keepidle; /* time before keepalive probes begin */
193 extern int tcp_keepintvl; /* time between keepalive probes */
194 extern int tcp_keepcnt; /* number of keepalives */
195 extern int tcp_delacktime; /* time before sending a delayed ACK */
196 extern int tcp_maxpersistidle;
197 extern int tcp_rexmit_initial;
198 extern int tcp_rexmit_min;
199 extern int tcp_rexmit_slop;
201 extern int tcp_ttl; /* time to live for TCP segs */
202 extern int tcp_backoff[];
203 extern int tcp_totbackoff;
204 extern int tcp_rexmit_drop_options;
206 extern int tcp_always_keepalive;
207 extern int tcp_finwait2_timeout;
208 extern int tcp_fast_finwait2_recycle;
210 VNET_DECLARE(int, tcp_pmtud_blackhole_detect);
211 #define V_tcp_pmtud_blackhole_detect VNET(tcp_pmtud_blackhole_detect)
212 VNET_DECLARE(int, tcp_pmtud_blackhole_mss);
213 #define V_tcp_pmtud_blackhole_mss VNET(tcp_pmtud_blackhole_mss)
214 VNET_DECLARE(int, tcp_v6pmtud_blackhole_mss);
215 #define V_tcp_v6pmtud_blackhole_mss VNET(tcp_v6pmtud_blackhole_mss)
217 void tcp_inpinfo_lock_del(struct inpcb *inp, struct tcpcb *tp);
219 void tcp_timer_init(void);
220 void tcp_timer_2msl(void *xtp);
221 void tcp_timer_discard(void *);
223 tcp_tw_2msl_scan(int reuse); /* XXX temporary? */
224 void tcp_timer_keep(void *xtp);
225 void tcp_timer_persist(void *xtp);
226 void tcp_timer_rexmt(void *xtp);
227 void tcp_timer_delack(void *xtp);
231 #endif /* !_NETINET_TCP_TIMER_H_ */