Re: IPv6 "is unreachable" route flapping

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

On 22/08/2019 18:58, Roy Marples wrote:
> On 22/08/2019 14:31, Roy Marples wrote:
> > On 22/08/2019 13:46, Paul Ripke wrote:
> > > > Does this attached patch help any?
> > >
> > > This is for the client (dhcpcd running) side? And/or the server 
> > > (rtadvd) side?
> > > I'll test it on a few machines and see what I see (I need to figure 
> > > out a nice
> > > way of upgrading the Pi).
> >
> > It's for the client.
>
> OK, while that patch is of use, it doesn't really solve the problem and 
> it's probably of limited use, but it does restore prior behaviour.
>
> There are two problems in play - firstly I broke dhcpcd, patch attached 
> to solve that.

Wups, old dhcpcd patch!
New one attached here :)

Roy

diff --git a/src/if-bsd.c b/src/if-bsd.c
index 6d5531cb..91f540bd 100644
--- a/src/if-bsd.c
+++ b/src/if-bsd.c
@@ -674,9 +674,15 @@ if_copyrt(struct dhcpcd_ctx *ctx, struct rt *rt, const struct rt_msghdr *rtm)
 		if (rt->rt_netmask.sa_family == 255) /* Why? */
 			rt->rt_netmask.sa_family = rt->rt_dest.sa_family;
 	}
-	/* dhcpcd likes an unspecified gateway to indicate via the link. */
-	if (rt->rt_flags & RTF_GATEWAY &&
-	    rti_info[RTAX_GATEWAY]->sa_family != AF_LINK)
+	/* dhcpcd likes an unspecified gateway to indicate via the link.
+	 * However we need to know if gateway was a link with an address. */
+	if (rti_info[RTAX_GATEWAY]->sa_family == AF_LINK) {
+		const struct sockaddr_dl *sdl;
+
+		sdl = (const struct sockaddr_dl*)rti_info[RTAX_GATEWAY];
+		if (sdl->sdl_alen != 0)
+			rt->rt_dflags |= RTDF_GATELINK;
+	} else if (rtm->rtm_flags & RTF_GATEWAY)
 		if_copysa(&rt->rt_gateway, rti_info[RTAX_GATEWAY]);
 	if (rtm->rtm_addrs & RTA_IFA)
 		if_copysa(&rt->rt_ifa, rti_info[RTAX_IFA]);
@@ -1079,17 +1085,9 @@ if_rtm(struct dhcpcd_ctx *ctx, const struct rt_msghdr *rtm)
 	 * existance with a hardware address.
 	 */
 	if (rt.rt_dest.sa_family == AF_INET6 && rt.rt_flags & RTF_HOST) {
-		struct sockaddr_in6 dest;
-		struct sockaddr_dl sdl;
-
-		memcpy(&dest, &rt.rt_dest, rt.rt_dest.sa_len);
-		if (rt.rt_gateway.sa_family == AF_LINK)
-			memcpy(&sdl, &rt.rt_gateway, rt.rt_gateway.sa_len);
-		else
-			sdl.sdl_alen = 0;
-		ipv6nd_neighbour(ctx, &dest.sin6_addr,
-		    rtm->rtm_type != RTM_DELETE && sdl.sdl_alen ?
-		    IPV6ND_REACHABLE : 0);
+		ipv6nd_neighbour(ctx, &rt.rt_ss_dest.sin6.sin6_addr,
+		    rtm->rtm_type != RTM_DELETE && rt.rt_dflags & RTDF_GATELINK
+		    ? IPV6ND_REACHABLE : 0);
 	}
 #endif
 
diff --git a/src/route.h b/src/route.h
index d1613943..74570fa7 100644
--- a/src/route.h
+++ b/src/route.h
@@ -92,6 +92,7 @@ struct rt {
 #define	RTDF_RA			0x08		/* Router Advertisement */
 #define	RTDF_DHCP		0x10		/* DHCP route */
 #define	RTDF_STATIC		0x20		/* Configured in dhcpcd */
+#define	RTDF_GATELINK		0x40		/* Gateway is on link */
 	size_t			rt_order;
 	rb_node_t		rt_tree;
 };