Dynamically calculate RA intervals when prefix lifetimes are short

diff --git a/src/router.c b/src/router.c
index dfbcf60..372c400 100644 (file)
--- a/src/router.c
+++ b/src/router.c
@@ -273,6 +273,7 @@ static void send_router_advert(struct uloop_timeout *event)
        // If not currently shutting down
        struct odhcpd_ipaddr addrs[RELAYD_MAX_PREFIXES];
        ssize_t ipcnt = 0;
+       uint64_t maxpreferred = 0;
 
        // If not shutdown
        if (event->cb) {
@@ -318,9 +319,13 @@ static void send_router_advert(struct uloop_timeout *event)
                        p = &adv.prefix[cnt++];
                }
 
-               if ((addr->addr.s6_addr[0] & 0xfe) != 0xfc && addr->preferred > 0)
+               if ((addr->addr.s6_addr[0] & 0xfe) != 0xfc && addr->preferred > 0) {
                        have_public = true;
 
+                       if (maxpreferred < 1000 * addr->preferred)
+                               maxpreferred = 1000 * addr->preferred;
+               }
+
                memcpy(&p->nd_opt_pi_prefix, &addr->addr, 8);
                p->nd_opt_pi_type = ND_OPT_PREFIX_INFORMATION;
                p->nd_opt_pi_len = 4;
@@ -453,10 +458,23 @@ static void send_router_advert(struct uloop_timeout *event)
 
        // Rearm timer if not shut down
        if (event->cb) {
+               uint32_t maxinterval = MaxRtrAdvInterval * 1000;
+               uint32_t mininterval = MinRtrAdvInterval * 1000;
+
+               if (maxpreferred > 0 && maxinterval > maxpreferred / 2) {
+                       maxinterval = maxpreferred / 2;
+                       if (maxinterval < 4000)
+                               maxinterval = 4000;
+
+                       if (maxinterval >= 9000)
+                               mininterval = maxinterval / 3;
+                       else
+                               mininterval = (maxinterval * 3) / 4;
+               }
+
                int msecs;
                odhcpd_urandom(&msecs, sizeof(msecs));
-               msecs = (labs(msecs) % (1000 * (MaxRtrAdvInterval
-                               - MinRtrAdvInterval))) + (MinRtrAdvInterval * 1000);
+               msecs = (labs(msecs) % (maxinterval - mininterval)) + mininterval;
                uloop_timeout_set(&iface->timer_rs, msecs);
        }
 }