IPv6: Improve comments on prior global for default route change

diff --git a/src/ipv6.c b/src/ipv6.c
index 46a1278e023b6ad89d099f7875056f206220940c..c746f775a0ada9d71a2d2432140d2e19f6a59b03 100644 (file)
--- a/src/ipv6.c
+++ b/src/ipv6.c
@@ -1115,8 +1115,17 @@ ipv6_anyglobal(struct interface *sifp)
        struct ipv6_addr *ia;
        struct interface *ifp;
 
-       /* IP6 source address selection does not care if we are a router
-        * or not, so just find a global address on any interface. */
+       /*
+        * IPv6 source address selection will prefer the outgoing interface,
+        * but will also use any other interface if it things the address is
+        * a better fit for the destination.
+        * This logic is pretty much baked into all kernels and you
+        * don't need to be a router either.
+        * We only have this logic to work around badly configured IPv6
+        * setups where there is a default router, but you're not handed
+        * a reachable address. This results in network timeouts which we
+        * want to actively avoid.
+        */
        TAILQ_FOREACH(ifp, sifp->ctx->ifaces, next) {
                ia = ipv6_ifanyglobal(ifp);
                if (ia != NULL)
@@ -2337,11 +2346,21 @@ inet6_raroutes(rb_tree_t *routes, struct dhcpcd_ctx *ctx)
                /* add default route */
                if (rap->lifetime == 0)
                        continue;
-               /* We only want to install a default route if we have
-                * an address that we can use other it.
-                * If we don't have any global addresses any request
-                * over the interface just times out.
-                * This avoids a badly setup IPv6 enabled router. */
+               /*
+                * We only want to install a default route if we have
+                * an address that we can use over it.
+                * If we don't have any global addresses then the link-local
+                * address would be used instead and we wouldn't reach
+                * our destination and even if we could, they wouldn't
+                * be able to reply back to us.
+                * This avoids timeouts on badly configured IPv6 setups
+                * where there is a default router but it or a DHCPv6 server
+                * doesn't hand out an address.
+                * If an address appears from anywhere, dhcpcd will spot this
+                * and then add the default like.
+                * Likewise, if all global addresses are removed then dhcpcd
+                * will remove the default route.
+                */
                if (ipv6_anyglobal(rap->iface) == NULL)
                        continue;
                rt = inet6_makerouter(rap);