Author: sbruno Date: Tue Oct 7 21:50:28 2014 New Revision: 272720 URL: https://svnweb.freebsd.org/changeset/base/272720
Log: Implement PLPMTUD blackhole detection (RFC 4821), inspired by code from xnu sources. If we encounter a network where ICMP is blocked the Needs Frag indicator may not propagate back to us. Attempt to downshift the mss once to a preconfigured value. Default this feature to off for now while we do not have a full PLPMTUD implementation in our stack. Adds the following new sysctl's for control: net.inet.tcp.pmtud_blackhole_detection -- turns on/off this feature net.inet.tcp.pmtud_blackhole_mss -- mss to try for ipv4 net.inet.tcp.v6pmtud_blackhole_mss -- mss to try for ipv6 Adds the following new sysctl's for monitoring: -- Number of times the code was activated to attempt a mss downshift net.inet.tcp.pmtud_blackhole_activated -- Number of times the blackhole mss was used in an attempt to downshift net.inet.tcp.pmtud_blackhole_min_activated -- Number of times that we failed to connect after we downshifted the mss net.inet.tcp.pmtud_blackhole_failed Phabricator: https://reviews.freebsd.org/D506 Reviewed by: rpaulo bz MFC after: 2 weeks Relnotes: yes Sponsored by: Limelight Networks Modified: head/sys/netinet/tcp_output.c head/sys/netinet/tcp_timer.c head/sys/netinet/tcp_var.h Modified: head/sys/netinet/tcp_output.c ============================================================================== --- head/sys/netinet/tcp_output.c Tue Oct 7 21:26:22 2014 (r272719) +++ head/sys/netinet/tcp_output.c Tue Oct 7 21:50:28 2014 (r272720) @@ -675,6 +675,12 @@ just_return: send: SOCKBUF_LOCK_ASSERT(&so->so_snd); + if (len > 0) { + if (len >= tp->t_maxseg) + tp->t_flags2 |= TF2_PLPMTU_MAXSEGSNT; + else + tp->t_flags2 &= ~TF2_PLPMTU_MAXSEGSNT; + } /* * Before ESTABLISHED, force sending of initial options * unless TCP set not to do any options. @@ -1303,8 +1309,12 @@ send: * * NB: Don't set DF on small MTU/MSS to have a safe fallback. */ - if (V_path_mtu_discovery && tp->t_maxopd > V_tcp_minmss) + if (V_path_mtu_discovery && tp->t_maxopd > V_tcp_minmss) { ip->ip_off |= htons(IP_DF); + tp->t_flags2 |= TF2_PLPMTU_PMTUD; + } else { + tp->t_flags2 &= ~TF2_PLPMTU_PMTUD; + } if (tp->t_state == TCPS_SYN_SENT) TCP_PROBE5(connect__request, NULL, tp, ip, tp, th); Modified: head/sys/netinet/tcp_timer.c ============================================================================== --- head/sys/netinet/tcp_timer.c Tue Oct 7 21:26:22 2014 (r272719) +++ head/sys/netinet/tcp_timer.c Tue Oct 7 21:50:28 2014 (r272720) @@ -66,6 +66,9 @@ __FBSDID("$FreeBSD$"); #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> @@ -127,6 +130,54 @@ SYSCTL_INT(_net_inet_tcp, OID_AUTO, rexm &tcp_rexmit_drop_options, 0, "Drop TCP options from 3rd and later retransmitted SYN"); +static VNET_DEFINE(int, tcp_pmtud_blackhole_detect); +#define V_tcp_pmtud_blackhole_detect VNET(tcp_pmtud_blackhole_detect) +SYSCTL_INT(_net_inet_tcp, OID_AUTO, pmtud_blackhole_detection, + CTLTYPE_INT|CTLFLAG_RW|CTLFLAG_VNET, + &VNET_NAME(tcp_pmtud_blackhole_detect), 0, + "Path MTU Discovery Black Hole Detection Enabled"); + +static VNET_DEFINE(int, tcp_pmtud_blackhole_activated); +#define V_tcp_pmtud_blackhole_activated \ + VNET(tcp_pmtud_blackhole_activated) +SYSCTL_INT(_net_inet_tcp, OID_AUTO, pmtud_blackhole_activated, + CTLTYPE_INT|CTLFLAG_RD|CTLFLAG_VNET, + &VNET_NAME(tcp_pmtud_blackhole_activated), 0, + "Path MTU Discovery Black Hole Detection, Activation Count"); + +static VNET_DEFINE(int, tcp_pmtud_blackhole_activated_min_mss); +#define V_tcp_pmtud_blackhole_activated_min_mss \ + VNET(tcp_pmtud_blackhole_activated_min_mss) +SYSCTL_INT(_net_inet_tcp, OID_AUTO, pmtud_blackhole_activated_min_mss, + CTLTYPE_INT|CTLFLAG_RD|CTLFLAG_VNET, + &VNET_NAME(tcp_pmtud_blackhole_activated_min_mss), 0, + "Path MTU Discovery Black Hole Detection, Activation Count at min MSS"); + +static VNET_DEFINE(int, tcp_pmtud_blackhole_failed); +#define V_tcp_pmtud_blackhole_failed VNET(tcp_pmtud_blackhole_failed) +SYSCTL_INT(_net_inet_tcp, OID_AUTO, pmtud_blackhole_failed, + CTLTYPE_INT|CTLFLAG_RD|CTLFLAG_VNET, + &VNET_NAME(tcp_pmtud_blackhole_failed), 0, + "Path MTU Discovery Black Hole Detection, Failure Count"); + +#ifdef INET +static VNET_DEFINE(int, tcp_pmtud_blackhole_mss) = 1200; +#define V_tcp_pmtud_blackhole_mss VNET(tcp_pmtud_blackhole_mss) +SYSCTL_INT(_net_inet_tcp, OID_AUTO, pmtud_blackhole_mss, + CTLTYPE_INT|CTLFLAG_RW|CTLFLAG_VNET, + &VNET_NAME(tcp_pmtud_blackhole_mss), 0, + "Path MTU Discovery Black Hole Detection lowered MSS"); +#endif + +#ifdef INET6 +static VNET_DEFINE(int, tcp_v6pmtud_blackhole_mss) = 1220; +#define V_tcp_v6pmtud_blackhole_mss VNET(tcp_v6pmtud_blackhole_mss) +SYSCTL_INT(_net_inet_tcp, OID_AUTO, v6pmtud_blackhole_mss, + CTLTYPE_INT|CTLFLAG_RW|CTLFLAG_VNET, + &VNET_NAME(tcp_v6pmtud_blackhole_mss), 0, + "Path MTU Discovery IPv6 Black Hole Detection lowered MSS"); +#endif + #ifdef RSS static int per_cpu_timers = 1; #else @@ -539,6 +590,7 @@ tcp_timer_rexmt(void * xtp) ostate = tp->t_state; #endif + INP_INFO_RLOCK(&V_tcbinfo); inp = tp->t_inpcb; /* @@ -640,6 +692,102 @@ tcp_timer_rexmt(void * xtp) rexmt = TCP_REXMTVAL(tp) * tcp_backoff[tp->t_rxtshift]; TCPT_RANGESET(tp->t_rxtcur, rexmt, tp->t_rttmin, TCPTV_REXMTMAX); + + if (V_tcp_pmtud_blackhole_detect && (tp->t_state == TCPS_ESTABLISHED)) { + int optlen; +#ifdef INET6 + int isipv6; +#endif + + if (((tp->t_flags2 & (TF2_PLPMTU_PMTUD|TF2_PLPMTU_MAXSEGSNT)) == + (TF2_PLPMTU_PMTUD|TF2_PLPMTU_MAXSEGSNT)) && + (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 + * negotiated with peer. + */ + /* Record that we may have found a black hole. */ + tp->t_flags2 |= TF2_PLPMTU_BLACKHOLE; + + /* Keep track of previous MSS. */ + optlen = tp->t_maxopd - tp->t_maxseg; + tp->t_pmtud_saved_maxopd = tp->t_maxopd; + + /* + * Reduce the MSS to blackhole value or to the default + * in an attempt to retransmit. + */ +#ifdef INET6 + isipv6 = (tp->t_inpcb->inp_vflag & INP_IPV6) ? 1 : 0; + if (isipv6 && + tp->t_maxopd > V_tcp_v6pmtud_blackhole_mss) { + /* Use the sysctl tuneable blackhole MSS. */ + tp->t_maxopd = V_tcp_v6pmtud_blackhole_mss; + V_tcp_pmtud_blackhole_activated++; + } else if (isipv6) { + /* Use the default MSS. */ + tp->t_maxopd = V_tcp_v6mssdflt; + /* + * Disable Path MTU Discovery when we switch to + * minmss. + */ + tp->t_flags2 &= ~TF2_PLPMTU_PMTUD; + V_tcp_pmtud_blackhole_activated_min_mss++; + } +#endif +#if defined(INET6) && defined(INET) + else +#endif +#ifdef INET + if (tp->t_maxopd > V_tcp_pmtud_blackhole_mss) { + /* Use the sysctl tuneable blackhole MSS. */ + tp->t_maxopd = V_tcp_pmtud_blackhole_mss; + V_tcp_pmtud_blackhole_activated++; + } else { + /* Use the default MSS. */ + tp->t_maxopd = V_tcp_mssdflt; + /* + * Disable Path MTU Discovery when we switch to + * minmss. + */ + tp->t_flags2 &= ~TF2_PLPMTU_PMTUD; + V_tcp_pmtud_blackhole_activated_min_mss++; + } +#endif + 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); + } else { + /* + * If further retransmissions are still unsuccessful + * with a lowered MTU, maybe this isn't a blackhole and + * we restore the previous MSS and blackhole detection + * flags. + */ + if ((tp->t_flags2 & TF2_PLPMTU_BLACKHOLE) && + (tp->t_rxtshift > 4)) { + tp->t_flags2 |= TF2_PLPMTU_PMTUD; + tp->t_flags2 &= ~TF2_PLPMTU_BLACKHOLE; + optlen = tp->t_maxopd - tp->t_maxseg; + tp->t_maxopd = tp->t_pmtud_saved_maxopd; + tp->t_maxseg = tp->t_maxopd - optlen; + V_tcp_pmtud_blackhole_failed++; + /* + * 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 Modified: head/sys/netinet/tcp_var.h ============================================================================== --- head/sys/netinet/tcp_var.h Tue Oct 7 21:26:22 2014 (r272719) +++ head/sys/netinet/tcp_var.h Tue Oct 7 21:50:28 2014 (r272720) @@ -200,6 +200,8 @@ struct tcpcb { u_int t_keepcnt; /* number of keepalives before close */ u_int t_tsomax; /* TSO total burst length limit in bytes */ + u_int t_pmtud_saved_maxopd; /* pre-blackhole MSS */ + u_int t_flags2; /* More tcpcb flags storage */ uint32_t t_ispare[6]; /* 5 UTO, 1 TBD */ uint32_t t_tsomaxsegcount; /* TSO maximum segment count */ @@ -278,6 +280,13 @@ struct tcpcb { #endif /* TCP_SIGNATURE */ /* + * Flags for PLPMTU handling, t_flags2 + */ +#define TF2_PLPMTU_BLACKHOLE 0x00000001 /* Possible PLPMTUD Black Hole. */ +#define TF2_PLPMTU_PMTUD 0x00000002 /* Allowed to attempt PLPMTUD. */ +#define TF2_PLPMTU_MAXSEGSNT 0x00000004 /* Last seg sent was full seg. */ + +/* * Structure to hold TCP options that are only used during segment * processing (in tcp_input), but not held in the tcpcb. * It's basically used to reduce the number of parameters _______________________________________________ svn-src-all@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/svn-src-all To unsubscribe, send any mail to "svn-src-all-unsubscr...@freebsd.org"
