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Index: sys/netinet/tcp_timer.c
===================================================================
--- sys/netinet/tcp_timer.c
+++ sys/netinet/tcp_timer.c
@@ -66,6 +66,9 @@
#include <netinet/tcp_fsm.h>
#include <netinet/tcp_timer.h>
#include <netinet/tcp_var.h>
+#ifdef INET6
+#include <netinet6/tcp6_var.h>
+#endif
#include <netinet/tcpip.h>
#ifdef TCPDEBUG
#include <netinet/tcp_debug.h>
@@ -119,6 +122,13 @@
SYSCTL_INT(_net_inet_tcp, OID_AUTO, keepcnt, CTLFLAG_RW, &tcp_keepcnt, 0,
"Number of keepalive probes to send");
+int tcp_pmtud_black_hole_detect = 0 ;
+SYSCTL_INT(_net_inet_tcp, OID_AUTO, pmtud_blackhole_detection, CTLTYPE_INT|CTLFLAG_RW,
+ &tcp_pmtud_black_hole_detect, 0, "Path MTU Discovery Black Hole Detection");
+
+int tcp_pmtud_black_hole_mss = 1200 ;
+SYSCTL_INT(_net_inet_tcp, OID_AUTO, pmtud_blackhole_mss, CTLTYPE_INT|CTLFLAG_RW,
+ &tcp_pmtud_black_hole_mss, 0, "Path MTU Discovery Black Hole Detection lowered MSS");
/* max idle probes */
int tcp_maxpersistidle;
@@ -539,6 +549,9 @@
ostate = tp->t_state;
#endif
+#if INET6
+ int isipv6 = (tp->t_inpcb->inp_vflag & INP_IPV4) == 0;
+#endif /* INET6 */
INP_INFO_RLOCK(&V_tcbinfo);
inp = tp->t_inpcb;
/*
@@ -640,6 +653,62 @@
rexmt = TCP_REXMTVAL(tp) * tcp_backoff[tp->t_rxtshift];
TCPT_RANGESET(tp->t_rxtcur, rexmt,
tp->t_rttmin, TCPTV_REXMTMAX);
+ if (tcp_pmtud_black_hole_detect && (tp->t_state == TCPS_ESTABLISHED)) {
+ int optlen = 0;
+ if ((tp->t_flags & TF_PMTUD) && (tp->t_rxtshift == 2)) {
+ /*
+ * Enter Path MTU Black-hole Detection mechanism:
+ * - Disable Path MTU Discovery (IP "DF" bit).
+ * - Reduce MTU to lower value than what we negociated with peer.
+ */
+ /* Disable Path MTU Discovery for now */
+ tp->t_flags &= ~TF_PMTUD;
+ /* Record that we may have found a black hole */
+ tp->t_flags |= TF_BLACKHOLE;
+ optlen = tp->t_maxopd - tp->t_maxseg;
+ /* Keep track of previous MSS */
+ tp->t_pmtud_saved_maxopd = tp->t_maxopd;
+ /* Reduce the MSS to intermediary value */
+ if (tp->t_maxopd > tcp_pmtud_black_hole_mss) {
+ tp->t_maxopd = tcp_pmtud_black_hole_mss;
+ } else {
+ tp->t_maxopd = /* use the default MSS */
+#if INET6
+ isipv6 ? V_tcp_v6mssdflt :
+#endif /* INET6 */
+ tcp_mssdflt;
+ }
+ tp->t_maxseg = tp->t_maxopd - optlen;
+
+ /*
+ * Reset the slow-start flight size
+ * as it may depend on the new MSS
+ */
+ if (CC_ALGO(tp)->conn_init != NULL)
+ CC_ALGO(tp)->conn_init(tp->ccv);
+ }
+ /*
+ * If further retransmissions are still unsuccessful with a lowered MTU,
+ * maybe this isn't a Black Hole and we restore the previous MSS and
+ * blackhole detection flags.
+ */
+ else {
+ if ((tp->t_flags & TF_BLACKHOLE) && (tp->t_rxtshift > 4)) {
+ tp->t_flags |= TF_PMTUD;
+ tp->t_flags &= ~TF_BLACKHOLE;
+ optlen = tp->t_maxopd - tp->t_maxseg;
+ tp->t_maxopd = tp->t_pmtud_saved_maxopd;
+ tp->t_maxseg = tp->t_maxopd - optlen;
+ /*
+ * Reset the slow-start flight size as it
+ * may depend on the new MSS
+ */
+ if (CC_ALGO(tp)->conn_init != NULL)
+ CC_ALGO(tp)->conn_init(tp->ccv);
+ }
+ }
+ }
+
/*
* Disable RFC1323 and SACK if we haven't got any response to
* our third SYN to work-around some broken terminal servers
Index: sys/netinet/tcp_var.h
===================================================================
--- sys/netinet/tcp_var.h
+++ sys/netinet/tcp_var.h
@@ -200,8 +200,9 @@
u_int t_keepcnt; /* number of keepalives before close */
u_int t_tsomax; /* tso burst length limit */
+ u_int t_pmtud_saved_maxopd; /* MSS saved before performing PMTU-D BlackHole detection */
- uint32_t t_ispare[8]; /* 5 UTO, 3 TBD */
+ uint32_t t_ispare[7]; /* 5 UTO, 3 TBD */
void *t_pspare2[4]; /* 1 TCP_SIGNATURE, 3 TBD */
uint64_t _pad[6]; /* 6 TBD (1-2 CC/RTT?) */
};
@@ -238,6 +239,9 @@
#define TF_ECN_SND_ECE 0x10000000 /* ECN ECE in queue */
#define TF_CONGRECOVERY 0x20000000 /* congestion recovery mode */
#define TF_WASCRECOVERY 0x40000000 /* was in congestion recovery */
+#define TF_BLACKHOLE 0x80000000 /* Path MTU Discovery Black Hole detection */
+#define TF_PMTUD 0x100000000 /* Perform Path MTU Discovery for this connection */
+
#define IN_FASTRECOVERY(t_flags) (t_flags & TF_FASTRECOVERY)
#define ENTER_FASTRECOVERY(t_flags) t_flags |= TF_FASTRECOVERY

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