From b15f1f564edcf7e5bcb88113af1b6e423317cb23 Mon Sep 17 00:00:00 2001
From: Jun-ichiro itojun Hagino <itojun@cvs.openbsd.org>
Date: Wed, 29 May 2002 23:38:59 +0000
Subject: force fragment to minimum link MTU (1280) when needed (when PMTUD
 does not take effect) - like icmp6 responses or foo-over-IPv6 tunnel.

---
 sys/netinet6/icmp6.c       | 10 ++++++++--
 sys/netinet6/in6_gif.c     | 11 +++++++++--
 sys/netinet6/ip6_output.c  |  4 +---
 sys/netinet6/ip6_var.h     |  3 ++-
 sys/netinet6/udp6_output.c |  4 ++--
 5 files changed, 22 insertions(+), 10 deletions(-)

(limited to 'sys/netinet6')

diff --git a/sys/netinet6/icmp6.c b/sys/netinet6/icmp6.c
index 6d4d27f9783..b61ef1ea4f5 100644
--- a/sys/netinet6/icmp6.c
+++ b/sys/netinet6/icmp6.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: icmp6.c,v 1.57 2002/05/29 07:54:59 itojun Exp $	*/
+/*	$OpenBSD: icmp6.c,v 1.58 2002/05/29 23:38:58 itojun Exp $	*/
 /*	$KAME: icmp6.c,v 1.217 2001/06/20 15:03:29 jinmei Exp $	*/
 
 /*
@@ -2212,7 +2212,13 @@ icmp6_reflect(m, off)
 
 	m->m_flags &= ~(M_BCAST|M_MCAST);
 
-	if (ip6_output(m, NULL, NULL, 0, NULL, &outif) != 0 && outif)
+	/*
+	 * To avoid a "too big" situation at an intermediate router
+	 * and the path MTU discovery process, specify the IPV6_MINMTU flag.
+	 * Note that only echo and node information replies are affected,
+	 * since the length of ICMP6 errors is limited to the minimum MTU.
+	 */
+	if (ip6_output(m, NULL, NULL, IPV6_MINMTU, NULL, &outif) != 0 && outif)
 		icmp6_ifstat_inc(outif, ifs6_out_error);
 
 	if (outif)
diff --git a/sys/netinet6/in6_gif.c b/sys/netinet6/in6_gif.c
index 5d151177f0f..126c062ba23 100644
--- a/sys/netinet6/in6_gif.c
+++ b/sys/netinet6/in6_gif.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: in6_gif.c,v 1.19 2001/12/07 09:16:07 itojun Exp $	*/
+/*	$OpenBSD: in6_gif.c,v 1.20 2002/05/29 23:38:58 itojun Exp $	*/
 /*	$KAME: in6_gif.c,v 1.43 2001/01/22 07:27:17 itojun Exp $	*/
 
 /*
@@ -194,7 +194,14 @@ in6_gif_output(ifp, family, m, rt)
 		}
 	}
 	
-	return(ip6_output(m, 0, &sc->gif_ro6, 0, 0, NULL));
+	/*
+	 * force fragmentation to minimum MTU, to avoid path MTU discovery.
+	 * it is too painful to ask for resend of inner packet, to achieve
+	 * path MTU discovery for encapsulated packets.
+	 */
+	error = ip6_output(m, 0, &sc->gif_ro6, IPV6_MINMTU, 0, NULL);
+
+	return error;
 }
 
 int in6_gif_input(mp, offp, proto)
diff --git a/sys/netinet6/ip6_output.c b/sys/netinet6/ip6_output.c
index a6a5b470f88..e1038027cb7 100644
--- a/sys/netinet6/ip6_output.c
+++ b/sys/netinet6/ip6_output.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: ip6_output.c,v 1.59 2002/05/29 07:54:59 itojun Exp $	*/
+/*	$OpenBSD: ip6_output.c,v 1.60 2002/05/29 23:38:58 itojun Exp $	*/
 /*	$KAME: ip6_output.c,v 1.172 2001/03/25 09:55:56 itojun Exp $	*/
 
 /*
@@ -713,12 +713,10 @@ ip6_output(m0, opt, ro, flags, im6o, ifpp)
 	 * The caller of this function may specify to use the minimum MTU
 	 * in some cases.
 	 */
-#ifdef IPV6_MINMTU
 	if (mtu > IPV6_MMTU) {
 		if ((flags & IPV6_MINMTU))
 			mtu = IPV6_MMTU;
 	}
-#endif
 
 	/* Fake scoped addresses */
 	if ((ifp->if_flags & IFF_LOOPBACK) != 0) {
diff --git a/sys/netinet6/ip6_var.h b/sys/netinet6/ip6_var.h
index 4c07d7c694f..f2179bde1c2 100644
--- a/sys/netinet6/ip6_var.h
+++ b/sys/netinet6/ip6_var.h
@@ -1,4 +1,4 @@
-/*	$OpenBSD: ip6_var.h,v 1.15 2002/05/28 03:04:38 itojun Exp $	*/
+/*	$OpenBSD: ip6_var.h,v 1.16 2002/05/29 23:38:58 itojun Exp $	*/
 /*	$KAME: ip6_var.h,v 1.33 2000/06/11 14:59:20 jinmei Exp $	*/
 
 /*
@@ -204,6 +204,7 @@ struct	ip6stat {
 /* flags passed to ip6_output as last parameter */
 #define	IPV6_DADOUTPUT		0x01	/* DAD */
 #define	IPV6_FORWARDING		0x02	/* most of IPv6 header exists */
+#define	IPV6_MINMTU		0x04	/* use minimum MTU (IPV6_USE_MIN_MTU) */
 
 extern struct	ip6stat ip6stat;	/* statistics */
 extern u_int32_t ip6_id;		/* fragment identifier */
diff --git a/sys/netinet6/udp6_output.c b/sys/netinet6/udp6_output.c
index c51cd703b10..98a042dbbf4 100644
--- a/sys/netinet6/udp6_output.c
+++ b/sys/netinet6/udp6_output.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: udp6_output.c,v 1.5 2001/12/06 04:19:26 itojun Exp $	*/
+/*	$OpenBSD: udp6_output.c,v 1.6 2002/05/29 23:38:58 itojun Exp $	*/
 /*	$KAME: udp6_output.c,v 1.21 2001/02/07 11:51:54 itojun Exp $	*/
 
 /*
@@ -264,7 +264,7 @@ udp6_output(in6p, m, addr6, control)
 		}
 
 		flags = 0;
-#ifdef IPV6_MINMTU
+#ifdef IN6P_MINMTU
 		if (in6p->in6p_flags & IN6P_MINMTU)
 			flags |= IPV6_MINMTU;
 #endif
-- 
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