Re: IPv6 "is unreachable" route flapping

[Roy Marples <roy%marples.name@localhost>]

On 21/08/2019 14:14, Paul Ripke wrote:
> I must be doing something silly, but I can't figure out what.
> Setup is a NetBSD 8.0 box running as router, dhcp6c getting a prefix
> over pppoe0, assigning it to alc0. This works fine, and IPv6 on this
> box is rock-solid. It also runs rtadvd on alc0.
>
> Client machines vary, but for example an Orange PI with netbsd-8.99.51
> and ip6mode autohost with dhcpcd gets intermittent IPv6 connectivity,
> and logs reachability flaps to the default router:
>
> Aug 21 00:48:57 armv7 dhcpcd[279]: emac0: fe80::52e5:49ff:fea6:f5d8 is unreachable, expiring it
> Aug 21 00:48:57 armv7 dhcpcd[279]: emac0: deleting route to 2001:44b8:31a3:5d00::/64
> Aug 21 00:48:57 armv7 dhcpcd[279]: emac0: deleting route to 2001:44b8:3158:7e00::/64
> Aug 21 00:48:57 armv7 dhcpcd[279]: emac0: deleting default route via fe80::52e5:49ff:fea6:f5d8
> Aug 21 00:48:57 armv7 dhcpcd[279]: emac0: fe80::52e5:49ff:fea6:f5d8 is reachable again
> Aug 21 00:48:57 armv7 dhcpcd[279]: emac0: adding route to 2001:44b8:3158:7e00::/64
> Aug 21 00:48:57 armv7 dhcpcd[279]: emac0: adding route to 2001:44b8:31a3:5d00::/64
> Aug 21 00:48:57 armv7 dhcpcd[279]: emac0: adding default route via fe80::52e5:49ff:fea6:f5d8
> Aug 21 00:52:10 armv7 dhcpcd[279]: emac0: adding route to 192.168.0.0/24
> Aug 21 00:52:10 armv7 dhcpcd[279]: emac0: pid 279 deleted route to 192.168.0.0/24

dhcpcd listens for RTM_ADD/RTM_DELETE messages.
If the destination matches the router address and it's RTM_DELETE or the 
gateway address is not AF_LINK or sdl_alen of the gateway address is 
zero then the kernel has lost reachability to the router and dhcpcd will 
expire it accordingly or it will mark the router as reachable.

You should be able to see this in `route monitor` output.

Does this attached patch help any?

Roy

Index: sys/netinet6/nd6.c
===================================================================
RCS file: /cvsroot/src/sys/netinet6/nd6.c,v
retrieving revision 1.257
diff -u -p -r1.257 nd6.c
--- sys/netinet6/nd6.c	14 Aug 2019 08:34:44 -0000	1.257
+++ sys/netinet6/nd6.c	21 Aug 2019 15:05:59 -0000
@@ -2225,11 +2225,17 @@ nd6_cache_lladdr(
 		break;
 	}
 
-#if 0
-	/* XXX should we send rtmsg as it used to be? */
-	if (do_update)
-		rt_newmsg(RTM_CHANGE, rt);  /* tell user process */
-#endif
+	if (do_update) {
+		struct sockaddr_in6 sin6;
+		struct rtentry *rt;
+
+		sockaddr_in6_init(&sin6, from, 0, 0, 0);
+		rt = rtalloc1(sin6tosa(&sin6), 0);
+		if (rt != NULL) {
+			rt_newmsg(RTM_CHANGE, rt);  /* tell user process */
+			rt_unref(rt);
+		}
+	}
 
 	if (ln != NULL) {
 		router = ln->ln_router;
Index: sys/netinet6/nd6_nbr.c
===================================================================
RCS file: /cvsroot/src/sys/netinet6/nd6_nbr.c,v
retrieving revision 1.166
diff -u -p -r1.166 nd6_nbr.c
--- sys/netinet6/nd6_nbr.c	29 Apr 2019 16:12:30 -0000	1.166
+++ sys/netinet6/nd6_nbr.c	21 Aug 2019 15:05:59 -0000
@@ -883,11 +883,18 @@ nd6_na_input(struct mbuf *m, int off, in
 	 */
 	ln->ln_asked = 0;
 	nd6_llinfo_release_pkts(ln, ifp);
-	/* FIXME */
-#if 0
-	if (rt_announce) /* tell user process about any new lladdr */
-		rt_newmsg(RTM_CHANGE, rt);
-#endif
+
+	if (rt_announce) {
+		struct sockaddr_in6 sin6;
+		struct rtentry *rt;
+
+		sockaddr_in6_init(&sin6, &taddr6, 0, 0, 0);
+		rt = rtalloc1(sin6tosa(&sin6), 0);
+		if (rt != NULL) {
+			rt_newmsg(RTM_CHANGE, rt);  /* tell user process */
+			rt_unref(rt);
+		}
+	}
 
  freeit:
 	if (ln != NULL)