DHCP6: Discard less preferred ADVERTISMENTs until IRT

If we get a preference value of 255 then request immediately.
More RFC 8415 18.2.1 support, inspired by #376.

diff --git a/src/dhcp6.c b/src/dhcp6.c
index 9c875a1a4155ba8a0d31401316186d6c0c620bc4..5d0050a573f0297fdcd740d0ba291285d26931fa 100644 (file)
--- a/src/dhcp6.c
+++ b/src/dhcp6.c
@@ -3302,7 +3302,7 @@ dhcp6_recvif(struct interface *ifp, const char *sfrom,
        size_t i;
        const char *op;
        struct dhcp6_state *state;
-       uint8_t *o;
+       uint8_t *o, preference = 0;
        uint16_t ol;
        const struct dhcp_opt *opt;
        const struct if_options *ifo;
@@ -3464,16 +3464,24 @@ dhcp6_recvif(struct interface *ifp, const char *sfrom,
                        valid_op = false;
                        break;
                }
+
+               o = dhcp6_findmoption(r, len, D6_OPTION_PREFERENCE, &ol);
+               if (o && ol == sizeof(uint8_t))
+                       preference = *o;
+
+               /* If we already have an advertisement check that this one
+                * has a higher preference value. */
                if (state->recv_len && state->recv->type == DHCP6_ADVERTISE) {
-                       /* We already have an advertismemnt.
-                        * RFC 8415 says we have to wait for the IRT to elapse.
-                        * To keep the same behaviour we won't do anything with
-                        * this. In the future we should make a lists of
-                        * ADVERTS and pick the "best" one. */
-                       logdebugx("%s: discarding ADVERTISEMENT from %s",
-                           ifp->name, sfrom);
-                       return;
+                       o = dhcp6_findmoption(state->recv, state->recv_len,
+                           D6_OPTION_PREFERENCE, &ol);
+                       if (o && ol == sizeof(uint8_t) && *o >= preference) {
+                               logdebugx(
+                                   "%s: discarding ADVERTISEMENT from %s (%u)",
+                                   ifp->name, sfrom, preference);
+                               return;
+                       }
                }
+
                /* RFC7083 */
                o = dhcp6_findmoption(r, len, D6_OPTION_SOL_MAX_RT, &ol);
                if (o && ol == sizeof(uint32_t)) {
@@ -3592,16 +3600,19 @@ dhcp6_recvif(struct interface *ifp, const char *sfrom,
                if (ia == NULL)
                        ia = TAILQ_FIRST(&state->addrs);
                if (ia == NULL)
-                       loginfox("%s: ADV (no address) from %s",
-                           ifp->name, sfrom);
+                       loginfox("%s: ADV (no address) from %s (%u)",
+                           ifp->name, sfrom, preference);
                else
-                       loginfox("%s: ADV %s from %s",
-                           ifp->name, ia->saddr, sfrom);
-               if (state->RTC > 1) {
-                        // IRT already elapsed, initiate request
+                       loginfox("%s: ADV %s from %s (%u)",
+                           ifp->name, ia->saddr, sfrom, preference);
+
+               /*
+                * RFC 8415 18.2.1 says we must collect until ADVERTISEMENTs
+                * until we get one with a preference of 255 or
+                * the initial RT has elpased.
+                */
+               if (preference == 255 || state->RTC > 1)
                        dhcp6_startrequest(ifp);
-               }
-               // We will request when the IRT elapses
                return;
        }