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More MTU discovery: avoid over-retransmission if route changes in the

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middle of a fully-open window.  Also, keep track of how many retransmits
we do as a result of MTU discovery.  This may actually do more work than
necessary, but it's an unusual condition...

Suggested by: Janey Hoe <janey@lcs.mit.edu>
This commit is contained in:
Garrett Wollman 1995-10-10 17:45:43 +00:00
parent 1448ea7e81
commit 143d7a5499
3 changed files with 22 additions and 21 deletions
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19
sys/netinet/tcp_subr.c
View File

@ -31,7 +31,7 @@
* SUCH DAMAGE.
*
* @(#)tcp_subr.c 8.2 (Berkeley) 5/24/95
* $Id: tcp_subr.c,v 1.16 1995/09/22 17:43:37 wollman Exp $
* $Id: tcp_subr.c,v 1.17 1995/10/03 16:54:15 wollman Exp $
*/
#include <sys/param.h>
@ -503,6 +503,8 @@ tcp_mtudisc(inp, errno)
offered = taop->tao_mssopt;
mss = rt->rt_rmx.rmx_mtu - sizeof(struct tcpiphdr);
mss = min(mss, offered);
if (tp->t_maxopd <= mss)
return;
tp->t_maxopd = mss;
if ((tp->t_flags & (TF_REQ_TSTMP|TF_NOOPT)) == TF_REQ_TSTMP &&
@ -523,15 +525,12 @@ tcp_mtudisc(inp, errno)
tp->t_maxseg = mss;
/*
* Nudge TCP output. Unfortunately, we have no way to know
* which packet that we sent is the failing one, but in the
* vast majority of cases we expect that it will be at the
* beginning of the window, so this should do the right
* thing (I hope).
*/
tp->snd_nxt = tp->snd_una;
tcp_output(tp);
if (SEQ_GT(tp->snd_una, tp->t_lastmturesend)) {
tcpstat.tcps_mturesent++;
tp->t_rtt = 0;
tp->snd_nxt = tp->t_lastmturesend = tp->snd_una;
tcp_output(tp);
}
}
}
#endif /* MTUDISC */

19
sys/netinet/tcp_timewait.c
View File

@ -31,7 +31,7 @@
* SUCH DAMAGE.
*
* @(#)tcp_subr.c 8.2 (Berkeley) 5/24/95
* $Id: tcp_subr.c,v 1.16 1995/09/22 17:43:37 wollman Exp $
* $Id: tcp_subr.c,v 1.17 1995/10/03 16:54:15 wollman Exp $
*/
#include <sys/param.h>
@ -503,6 +503,8 @@ tcp_mtudisc(inp, errno)
offered = taop->tao_mssopt;
mss = rt->rt_rmx.rmx_mtu - sizeof(struct tcpiphdr);
mss = min(mss, offered);
if (tp->t_maxopd <= mss)
return;
tp->t_maxopd = mss;
if ((tp->t_flags & (TF_REQ_TSTMP|TF_NOOPT)) == TF_REQ_TSTMP &&
@ -523,15 +525,12 @@ tcp_mtudisc(inp, errno)
tp->t_maxseg = mss;
/*
* Nudge TCP output. Unfortunately, we have no way to know
* which packet that we sent is the failing one, but in the
* vast majority of cases we expect that it will be at the
* beginning of the window, so this should do the right
* thing (I hope).
*/
tp->snd_nxt = tp->snd_una;
tcp_output(tp);
if (SEQ_GT(tp->snd_una, tp->t_lastmturesend)) {
tcpstat.tcps_mturesent++;
tp->t_rtt = 0;
tp->snd_nxt = tp->t_lastmturesend = tp->snd_una;
tcp_output(tp);
}
}
}
#endif /* MTUDISC */

5
sys/netinet/tcp_var.h
View File

@ -31,7 +31,7 @@
* SUCH DAMAGE.
*
* @(#)tcp_var.h 8.4 (Berkeley) 5/24/95
* $Id: tcp_var.h,v 1.17 1995/09/22 07:40:18 peter Exp $
* $Id: tcp_var.h,v 1.18 1995/10/04 20:49:03 wollman Exp $
*/
#ifndef _NETINET_TCP_VAR_H_
@ -141,6 +141,8 @@ struct tcpcb {
caddr_t t_tuba_pcb; /* next level down pcb for TCP over z */
/* More RTT stuff */
u_long t_rttupdated; /* number of times rtt sampled */
/* For MTU discovery */
tcp_seq t_lastmturesend; /* seq of resend for mtu discovery */
};
/*
@ -287,6 +289,7 @@ struct tcpstat {
u_long tcps_usedssthresh; /* times ssthresh initialized from rt*/
u_long tcps_persistdrop; /* timeout in persist state */
u_long tcps_badsyn; /* bogus SYN, e.g. premature ACK */
u_long tcps_mturesent; /* resends due to MTU discovery */
};
/*