diff --git a/sbin/ifconfig/Makefile b/sbin/ifconfig/Makefile
index ae5b01682404..9e0f73bba245 100644
--- a/sbin/ifconfig/Makefile
+++ b/sbin/ifconfig/Makefile
@@ -51,6 +51,9 @@ SRCS+=	ifpfsync.c		# pfsync(4) support
 SRCS+=	ifbridge.c		# bridge support
 SRCS+=	iflagg.c		# lagg support
 
+.if ${MK_EXPERIMENTAL} != "no"
+CFLAGS+= -DDRAFT_IETF_6MAN_IPV6ONLY_FLAG
+.endif
 .if ${MK_INET6_SUPPORT} != "no"
 CFLAGS+= -DINET6
 .endif
diff --git a/sbin/ifconfig/af_nd6.c b/sbin/ifconfig/af_nd6.c
index 8c576117e226..2ce97394c700 100644
--- a/sbin/ifconfig/af_nd6.c
+++ b/sbin/ifconfig/af_nd6.c
@@ -57,9 +57,17 @@ static const char rcsid[] =
 #include "ifconfig.h"
 
 #define	MAX_SYSCTL_TRY	5
+#ifdef DRAFT_IETF_6MAN_IPV6ONLY_FLAG
+#define	ND6BITS	"\020\001PERFORMNUD\002ACCEPT_RTADV\003PREFER_SOURCE" \
+		"\004IFDISABLED\005DONT_SET_IFROUTE\006AUTO_LINKLOCAL" \
+		"\007NO_RADR\010NO_PREFER_IFACE\011NO_DAD" \
+		"\012IPV6_ONLY" \
+		"\020DEFAULTIF"
+#else
 #define	ND6BITS	"\020\001PERFORMNUD\002ACCEPT_RTADV\003PREFER_SOURCE" \
 		"\004IFDISABLED\005DONT_SET_IFROUTE\006AUTO_LINKLOCAL" \
 		"\007NO_RADR\010NO_PREFER_IFACE\011NO_DAD\020DEFAULTIF"
+#endif
 
 static int isnd6defif(int);
 void setnd6flags(const char *, int, int, const struct afswtch *);
diff --git a/sys/net/if_ethersubr.c b/sys/net/if_ethersubr.c
index 28dac295e077..628e32b17642 100644
--- a/sys/net/if_ethersubr.c
+++ b/sys/net/if_ethersubr.c
@@ -475,6 +475,26 @@ ether_output_frame(struct ifnet *ifp, struct mbuf *m)
 			return (0);
 	}
 
+#ifdef EXPERIMENTAL
+#if defined(INET6) && defined(INET)
+	/* draft-ietf-6man-ipv6only-flag */
+	/* Catch ETHERTYPE_IP, and ETHERTYPE_ARP if we are v6-only. */
+	if ((ND_IFINFO(ifp)->flags & ND6_IFF_IPV6_ONLY) != 0) {
+		struct ether_header *eh;
+
+		eh = mtod(m, struct ether_header *);
+		switch (ntohs(eh->ether_type)) {
+		case ETHERTYPE_IP:
+		case ETHERTYPE_ARP:
+			m_freem(m);
+			return (EAFNOSUPPORT);
+			/* NOTREACHED */
+			break;
+		};
+	}
+#endif
+#endif
+
 	/*
 	 * Queue message on interface, update output statistics if
 	 * successful, and start output if interface not yet active.
diff --git a/sys/netinet/icmp6.h b/sys/netinet/icmp6.h
index 310684b8b47d..d4da06d0ff5e 100644
--- a/sys/netinet/icmp6.h
+++ b/sys/netinet/icmp6.h
@@ -244,6 +244,10 @@ struct nd_router_advert {	/* router advertisement */
 #define ND_RA_FLAG_RTPREF_LOW	0x18 /* 00011000 */
 #define ND_RA_FLAG_RTPREF_RSV	0x10 /* 00010000 */
 
+#ifdef EXPERIMENTAL
+#define	ND_RA_FLAG_IPV6_ONLY	0x02 /* draft-ietf-6man-ipv6only-flag */
+#endif
+
 #define nd_ra_router_lifetime	nd_ra_hdr.icmp6_data16[1]
 
 struct nd_neighbor_solicit {	/* neighbor solicitation */
diff --git a/sys/netinet6/nd6.h b/sys/netinet6/nd6.h
index cabfeec0dbac..7544d23c6660 100644
--- a/sys/netinet6/nd6.h
+++ b/sys/netinet6/nd6.h
@@ -90,6 +90,9 @@ struct nd_ifinfo {
 #define	ND6_IFF_NO_RADR		0x40
 #define ND6_IFF_NO_PREFER_IFACE	0x80 /* XXX: not related to ND. */
 #define ND6_IFF_NO_DAD		0x100
+#ifdef EXPERIMENTAL
+#define	ND6_IFF_IPV6_ONLY	0x200 /* draft-ietf-6man-ipv6only-flag */
+#endif
 
 #ifdef _KERNEL
 #define ND_IFINFO(ifp) \
diff --git a/sys/netinet6/nd6_rtr.c b/sys/netinet6/nd6_rtr.c
index ec1aa13730ca..e00a0d857b5c 100644
--- a/sys/netinet6/nd6_rtr.c
+++ b/sys/netinet6/nd6_rtr.c
@@ -204,6 +204,37 @@ nd6_rs_input(struct mbuf *m, int off, int icmp6len)
 	m_freem(m);
 }
 
+#ifdef EXPERIMENTAL
+/*
+ * An initial update routine for draft-ietf-6man-ipv6only-flag.
+ * We need to iterate over all default routers for the given
+ * interface to see whether they are all advertising the "6"
+ * (IPv6-Only) flag.  If they do set, otherwise unset, the
+ * interface flag we later use to filter on.
+ */
+static void
+defrtr_ipv6_only_ifp(struct ifnet *ifp)
+{
+	struct nd_defrouter *dr;
+	bool ipv6_only;
+
+	ipv6_only = true;
+	ND6_RLOCK();
+	TAILQ_FOREACH(dr, &V_nd_defrouter, dr_entry)
+		if (dr->ifp == ifp &&
+		    (dr->raflags & ND_RA_FLAG_IPV6_ONLY) == 0)
+			ipv6_only = false;
+	ND6_RUNLOCK();
+
+	IF_AFDATA_WLOCK(ifp);
+	if (ipv6_only)
+		ND_IFINFO(ifp)->flags |= ND6_IFF_IPV6_ONLY;
+	else
+		ND_IFINFO(ifp)->flags &= ~ND6_IFF_IPV6_ONLY;
+	IF_AFDATA_WUNLOCK(ifp);
+}
+#endif
+
 /*
  * Receive Router Advertisement Message.
  *
@@ -319,6 +350,9 @@ nd6_ra_input(struct mbuf *m, int off, int icmp6len)
 		}
 	}
 	dr = defrtrlist_update(&dr0);
+#ifdef EXPERIMENTAL
+	defrtr_ipv6_only_ifp(ifp);
+#endif
     }
 
 	/*
@@ -692,6 +726,10 @@ defrouter_del(struct nd_defrouter *dr)
 	if (ND_IFINFO(dr->ifp)->flags & ND6_IFF_ACCEPT_RTADV)
 		rt6_flush(&dr->rtaddr, dr->ifp);
 
+#ifdef EXPERIMENTAL
+	defrtr_ipv6_only_ifp(dr->ifp);
+#endif
+
 	if (dr->installed) {
 		deldr = dr;
 		defrouter_delreq(dr);
diff --git a/usr.sbin/ndp/Makefile b/usr.sbin/ndp/Makefile
index c2ff3090b495..52d8304a436a 100644
--- a/usr.sbin/ndp/Makefile
+++ b/usr.sbin/ndp/Makefile
@@ -13,6 +13,8 @@
 # A PARTICULAR PURPOSE.
 # $FreeBSD$
 
+.include <src.opts.mk>
+
 .PATH: ${SRCTOP}/contrib/tcpdump
 
 PROG=	ndp
@@ -22,6 +24,11 @@ SRCS=	ndp.c gmt2local.c
 CFLAGS+= -I. -I${.CURDIR} -I${SRCTOP}/contrib/tcpdump
 CFLAGS+= -D_U_=""
 
+.if ${MK_EXPERIMENTAL} != "no"
+CFLAGS+=	-DEXPERIMENTAL
+CFLAGS+=	-DDRAFT_IETF_6MAN_IPV6ONLY_FLAG
+.endif
+
 WARNS?=	3
 
 .include <bsd.prog.mk>
diff --git a/usr.sbin/ndp/ndp.c b/usr.sbin/ndp/ndp.c
index 10e186d1d9f3..a006006aab3c 100644
--- a/usr.sbin/ndp/ndp.c
+++ b/usr.sbin/ndp/ndp.c
@@ -1096,6 +1096,9 @@ rtrlist()
 		printf(", flags=%s%s",
 		    p->flags & ND_RA_FLAG_MANAGED ? "M" : "",
 		    p->flags & ND_RA_FLAG_OTHER   ? "O" : "");
+#ifdef DRAFT_IETF_6MAN_IPV6ONLY_FLAG
+		printf("%s", p->flags & ND_RA_FLAG_IPV6_ONLY ? "6" : "");
+#endif
 		rtpref = ((p->flags & ND_RA_FLAG_RTPREF_MASK) >> 3) & 0xff;
 		printf(", pref=%s", rtpref_str[rtpref]);
 
diff --git a/usr.sbin/rtadvd/Makefile b/usr.sbin/rtadvd/Makefile
index 5d627e55b265..920c6d966aff 100644
--- a/usr.sbin/rtadvd/Makefile
+++ b/usr.sbin/rtadvd/Makefile
@@ -14,11 +14,18 @@
 #
 # $FreeBSD$
 
+.include <src.opts.mk>
+
 PROG=	rtadvd
 MAN=	rtadvd.conf.5 rtadvd.8
 SRCS=	rtadvd.c rrenum.c advcap.c if.c config.c timer.c timer_subr.c	\
 	control.c control_server.c
 
+.if ${MK_EXPERIMENTAL} != "no"
+CFLAGS+=	-DEXPERIMENTAL
+CFLAGS+=	-DDRAFT_IETF_6MAN_IPV6ONLY_FLAG
+.endif
+
 LIBADD=	util
 
 WARNS?=	1
diff --git a/usr.sbin/rtadvd/config.c b/usr.sbin/rtadvd/config.c
index cd7134cecae2..f537ace0c25f 100644
--- a/usr.sbin/rtadvd/config.c
+++ b/usr.sbin/rtadvd/config.c
@@ -437,6 +437,10 @@ getconfig(struct ifinfo *ifi)
 			}
 			val |= ND_RA_FLAG_RTPREF_LOW;
 		}
+#ifdef DRAFT_IETF_6MAN_IPV6ONLY_FLAG
+		if (strchr(flagstr, '6'))
+			val |= ND_RA_FLAG_IPV6_ONLY;
+#endif
 	} else
 		MAYHAVE(val, "raflags", 0);
 
@@ -452,6 +456,9 @@ getconfig(struct ifinfo *ifi)
 		    __func__, rai->rai_rtpref, ifi->ifi_ifname);
 		goto getconfig_free_rai;
 	}
+#ifdef DRAFT_IETF_6MAN_IPV6ONLY_FLAG
+	rai->rai_ipv6onlyflg = val & ND_RA_FLAG_IPV6_ONLY;
+#endif
 
 	MAYHAVE(val, "rltime", rai->rai_maxinterval * 3);
 	if ((uint16_t)val && ((uint16_t)val < rai->rai_maxinterval ||
@@ -1406,6 +1413,10 @@ make_packet(struct rainfo *rai)
 		rai->rai_managedflg ? ND_RA_FLAG_MANAGED : 0;
 	ra->nd_ra_flags_reserved |=
 		rai->rai_otherflg ? ND_RA_FLAG_OTHER : 0;
+#ifdef DRAFT_IETF_6MAN_IPV6ONLY_FLAG
+	ra->nd_ra_flags_reserved |=
+		rai->rai_ipv6onlyflg ? ND_RA_FLAG_IPV6_ONLY : 0;
+#endif
 	ra->nd_ra_router_lifetime = htons(rai->rai_lifetime);
 	ra->nd_ra_reachable = htonl(rai->rai_reachabletime);
 	ra->nd_ra_retransmit = htonl(rai->rai_retranstimer);
diff --git a/usr.sbin/rtadvd/rtadvd.c b/usr.sbin/rtadvd/rtadvd.c
index d46185876444..d7237f06c223 100644
--- a/usr.sbin/rtadvd/rtadvd.c
+++ b/usr.sbin/rtadvd/rtadvd.c
@@ -1160,6 +1160,19 @@ ra_input(int len, struct nd_router_advert *nra,
 			sizeof(ntopbuf)), on_off[rai->rai_otherflg]);
 		inconsistent++;
 	}
+#ifdef DRAFT_IETF_6MAN_IPV6ONLY_FLAG
+	/* 6 flag */
+	if ((nra->nd_ra_flags_reserved & ND_RA_FLAG_IPV6_ONLY) !=
+	    rai->rai_ipv6onlyflg) {
+		syslog(LOG_NOTICE,
+		    "6 flag inconsistent on %s:"
+		    " %s from %s, %s from us",
+		    ifi->ifi_ifname, on_off[!rai->rai_ipv6onlyflg],
+		    inet_ntop(AF_INET6, &from->sin6_addr, ntopbuf,
+			sizeof(ntopbuf)), on_off[rai->rai_ipv6onlyflg]);
+		inconsistent++;
+	}
+#endif
 	/* Reachable Time */
 	reachabletime = ntohl(nra->nd_ra_reachable);
 	if (reachabletime && rai->rai_reachabletime &&
diff --git a/usr.sbin/rtadvd/rtadvd.h b/usr.sbin/rtadvd/rtadvd.h
index 005a42c2038a..885d2fbb3c80 100644
--- a/usr.sbin/rtadvd/rtadvd.h
+++ b/usr.sbin/rtadvd/rtadvd.h
@@ -196,6 +196,9 @@ struct	rainfo {
 	uint16_t	rai_mininterval;	/* MinRtrAdvInterval */
 	int 	rai_managedflg;		/* AdvManagedFlag */
 	int	rai_otherflg;		/* AdvOtherConfigFlag */
+#ifdef DRAFT_IETF_6MAN_IPV6ONLY_FLAG
+	int	rai_ipv6onlyflg;	/* AdvIPv6OnlyFlag */
+#endif
 
 	int	rai_rtpref;		/* router preference */
 	uint32_t	rai_linkmtu;		/* AdvLinkMTU */