Don't send requests to sources with very old sequence numbers.

This avoids repeatedly sending requests to a source that has just rebooted
and lost its sequence number.

route.c

@@ -422,13 +422,13 @@ update_route(const unsigned char *a, const unsigned char *p, unsigned char plen,
         if(feasible)
             trigger_route_change(route, oldsrc, oldmetric);
         else
-            send_unfeasible_request(metric, a, p, plen);
+            send_unfeasible_request(seqno, metric, a, p, plen);
 
         if(lost)
             route_lost(oldsrc, oldmetric);
     } else {
         if(!feasible) {
-            send_unfeasible_request(metric, a, p, plen);
+            send_unfeasible_request(seqno, metric, a, p, plen);
             return NULL;
         }
         if(refmetric >= INFINITY)
@@ -459,7 +459,8 @@ update_route(const unsigned char *a, const unsigned char *p, unsigned char plen,
 /* We just received an unfeasible update.  If it's any good, send
    a request for a new seqno. */
 void
-send_unfeasible_request(unsigned short metric, const unsigned char *a,
+send_unfeasible_request(unsigned short seqno, unsigned short metric,
+                        const unsigned char *a,
                         const unsigned char *prefix, unsigned char plen)
 {
     struct route *route = find_installed_route(prefix, plen);
@@ -468,6 +469,11 @@ send_unfeasible_request(unsigned short metric, const unsigned char *a,
     if(src == NULL)
         return;
 
+    if(seqno_minus(src->seqno, seqno) < 5) {
+        /* Probably a source that lost its seqno.  Let it time-out. */
+        return;
+    }
+
     if(!route || route->metric >= metric + 256) {
         send_request_resend(prefix, plen,
                             src->metric >= INFINITY ?

route.h

@@ -65,7 +65,8 @@ struct route *update_route(const unsigned char *a,
                            unsigned short seqno, unsigned short refmetric,
                            struct neighbour *neigh,
                            const unsigned char *nexthop);
-void send_unfeasible_request(unsigned short metric, const unsigned char *a,
+void send_unfeasible_request(unsigned short seqno, unsigned short metric,
+                             const unsigned char *a,
                              const unsigned char *prefix, unsigned char plen);
 void consider_route(struct route *route);
 void send_triggered_update(struct route *route,