Introduce MTU option.

The MTU option is used in Router Advertisement messages to ensure that
all nodes on a link use the same MTU value in those cases where the link
MTU is not well known.

Feedback (thank you!) and OK from florian@

6 files changed, 33 insertions, 8 deletions

diff --git a/usr.sbin/rad/frontend.c b/usr.sbin/rad/frontend.c
index b06fa43038c..d44701d7fde 100644
--- a/usr.sbin/rad/frontend.c
+++ b/usr.sbin/rad/frontend.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: frontend.c,v 1.11 2018/07/18 09:10:50 florian Exp $	*/
+/*	$OpenBSD: frontend.c,v 1.12 2018/07/20 17:55:09 bket Exp $	*/
 
 /*
  * Copyright (c) 2018 Florian Obser <florian@openbsd.org>
@@ -887,6 +887,7 @@ void
 build_packet(struct ra_iface *ra_iface)
 {
 	struct nd_router_advert		*ra;
+	struct nd_opt_mtu		*ndopt_mtu;
 	struct nd_opt_prefix_info	*ndopt_pi;
 	struct ra_iface_conf		*ra_iface_conf;
 	struct ra_options_conf		*ra_options_conf;
@@ -904,6 +905,8 @@ build_packet(struct ra_iface *ra_iface)
 	ra_options_conf = &ra_iface_conf->ra_options;
 
 	len = sizeof(*ra);
+	if (ra_options_conf->mtu > 0)
+		len += sizeof(*ndopt_mtu);
 	len += sizeof(*ndopt_pi) * ra_iface->prefix_count;
 	if (ra_iface_conf->rdnss_count > 0)
 		len += sizeof(*ndopt_rdnss) + ra_iface_conf->rdnss_count *
@@ -940,6 +943,15 @@ build_packet(struct ra_iface *ra_iface)
 	ra->nd_ra_retransmit = htonl(ra_options_conf->retrans_timer);
 	p += sizeof(*ra);
 
+	if (ra_options_conf->mtu > 0) {
+		ndopt_mtu = (struct nd_opt_mtu *)p;
+		ndopt_mtu->nd_opt_mtu_type = ND_OPT_MTU;
+		ndopt_mtu->nd_opt_mtu_len = 1;
+		ndopt_mtu->nd_opt_mtu_reserved = 0;
+		ndopt_mtu->nd_opt_mtu_mtu = htonl(ra_options_conf->mtu);
+		p += sizeof(*ndopt_mtu);
+	}
+
 	SIMPLEQ_FOREACH(ra_prefix_conf, &ra_iface->prefixes, entry) {
 		ndopt_pi = (struct nd_opt_prefix_info *)p;
 		memset(ndopt_pi, 0, sizeof(*ndopt_pi));
diff --git a/usr.sbin/rad/parse.y b/usr.sbin/rad/parse.y
index 70c3819e4a5..e0a4e1386a2 100644
--- a/usr.sbin/rad/parse.y
+++ b/usr.sbin/rad/parse.y
@@ -1,4 +1,4 @@
-/*	$OpenBSD: parse.y,v 1.5 2018/07/20 17:48:58 florian Exp $	*/
+/*	$OpenBSD: parse.y,v 1.6 2018/07/20 17:55:09 bket Exp $	*/
 
 /*
  * Copyright (c) 2018 Florian Obser <florian@openbsd.org>
@@ -115,7 +115,7 @@ typedef struct {
 %token	DEFAULT ROUTER HOP LIMIT MANAGED ADDRESS
 %token	CONFIGURATION OTHER LIFETIME REACHABLE TIME RETRANS TIMER
 %token	AUTO PREFIX VALID PREFERRED LIFETIME ONLINK AUTONOMOUS
-%token	ADDRESS_CONFIGURATION DNS NAMESERVER SEARCH
+%token	ADDRESS_CONFIGURATION DNS NAMESERVER SEARCH MTU
 
 %token	<v.string>	STRING
 %token	<v.number>	NUMBER
@@ -209,6 +209,9 @@ ra_opt_block	: DEFAULT ROUTER yesno {
 		| RETRANS TIMER NUMBER {
 			ra_options->retrans_timer = $3;
 		}
+		| MTU NUMBER {
+			ra_options->mtu = $2;
+		}
 		;
 
 optnl		: '\n' optnl		/* zero or more newlines */
@@ -424,6 +427,7 @@ lookup(char *s)
 		{"lifetime",		LIFETIME},
 		{"limit",		LIMIT},
 		{"managed",		MANAGED},
+		{"mtu",			MTU},
 		{"nameserver",		NAMESERVER},
 		{"no",			NO},
 		{"on-link",		ONLINK},
diff --git a/usr.sbin/rad/printconf.c b/usr.sbin/rad/printconf.c
index 1614fba0e04..1f9e1f72b1c 100644
--- a/usr.sbin/rad/printconf.c
+++ b/usr.sbin/rad/printconf.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: printconf.c,v 1.3 2018/07/20 13:17:02 florian Exp $	*/
+/*	$OpenBSD: printconf.c,v 1.4 2018/07/20 17:55:09 bket Exp $	*/
 
 /*
  * Copyright (c) 2018 Florian Obser <florian@openbsd.org>
@@ -54,6 +54,8 @@ print_ra_options(const char *indent, const struct ra_options_conf *ra_options)
 	printf("%srouter lifetime %d\n", indent, ra_options->router_lifetime);
 	printf("%sreachable time %u\n", indent, ra_options->reachable_time);
 	printf("%sretrans timer %u\n", indent, ra_options->retrans_timer);
+	if (ra_options->mtu > 0)
+		printf("%smtu %u\n", indent, ra_options->mtu);
 }
 
 void
diff --git a/usr.sbin/rad/rad.c b/usr.sbin/rad/rad.c
index 4652e1e0fb7..7885066a3ea 100644
--- a/usr.sbin/rad/rad.c
+++ b/usr.sbin/rad/rad.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: rad.c,v 1.9 2018/07/18 14:43:34 florian Exp $	*/
+/*	$OpenBSD: rad.c,v 1.10 2018/07/20 17:55:09 bket Exp $	*/
 
 /*
  * Copyright (c) 2018 Florian Obser <florian@openbsd.org>
@@ -716,6 +716,7 @@ config_new_empty(void)
 	xconf->ra_options.router_lifetime = 1800;
 	xconf->ra_options.reachable_time = 0;
 	xconf->ra_options.retrans_timer = 0;
+	xconf->ra_options.mtu = 0;
 
 	return (xconf);
 }
diff --git a/usr.sbin/rad/rad.conf.5 b/usr.sbin/rad/rad.conf.5
index 36d100513b8..ee688343aed 100644
--- a/usr.sbin/rad/rad.conf.5
+++ b/usr.sbin/rad/rad.conf.5
@@ -1,4 +1,4 @@
-.\"	$OpenBSD: rad.conf.5,v 1.7 2018/07/20 13:17:02 florian Exp $
+.\"	$OpenBSD: rad.conf.5,v 1.8 2018/07/20 17:55:09 bket Exp $
 .\"
 .\" Copyright (c) 2018 Florian Obser <florian@openbsd.org>
 .\" Copyright (c) 2005 Esben Norby <norby@openbsd.org>
@@ -87,6 +87,11 @@ The default is 1800 seconds.
 .\" XXX
 .\" .It Ic retrans timer Ar number
 .\" XXX
+.It Ic mtu Ar bytes
+The MTU option is used in Router Advertisement messages to ensure that all
+nodes on a link use the same MTU value in those cases where the link MTU
+is not well known.
+The default is 0, meaning unspecified by this router.
 .El
 .Sh INTERFACES
 A list of interfaces to send advertisments on:
diff --git a/usr.sbin/rad/rad.h b/usr.sbin/rad/rad.h
index db80d7c772d..a8b8ba116c4 100644
--- a/usr.sbin/rad/rad.h
+++ b/usr.sbin/rad/rad.h
@@ -1,4 +1,4 @@
-/*	$OpenBSD: rad.h,v 1.11 2018/07/15 09:28:21 florian Exp $	*/
+/*	$OpenBSD: rad.h,v 1.12 2018/07/20 17:55:09 bket Exp $	*/
 
 /*
  * Copyright (c) 2018 Florian Obser <florian@openbsd.org>
@@ -76,7 +76,7 @@ enum imsg_type {
 	IMSG_SOCKET_IPC
 };
 
-/* RFC 4861 Section 4.2 */
+/* RFC 4861 Sections 4.2 and 4.6.4 */
 struct ra_options_conf {
 	int		dfr;			/* is default router? */
 	int		cur_hl;			/* current hop limit */
@@ -85,6 +85,7 @@ struct ra_options_conf {
 	int		router_lifetime;	/* default router lifetime */
 	uint32_t	reachable_time;
 	uint32_t	retrans_timer;
+	uint32_t	mtu;
 };
 
 /* RFC 4861 Section 4.6.2 */