Do not select servers that are known to not give replies.

git-svn-id: file:///svn/unbound/trunk@427 be551aaa-1e26-0410-a405-d3ace91eadb9

doc/Changelog

@@ -2,6 +2,11 @@
 	- delete of mesh does a postorder traverse of the tree.
 	- found and fixed a memory leak. For TTL=0 messages, that would
 	  not be cached, instead the msg-replyinfo structure was leaked.
+	- changed server selection so it will filter out hosts that are
+	  unresponsive. This is defined as a host with the maximum rto value.
+	  This means that unbound tried the host for retries up to 120 secs.
+	  The rto value will time out after host-ttl seconds from the cache.
+	  This keeps such unresolvable queries from taking up resources.
 
 26 June 2007: Wouter
 	- mesh is called by worker, and iterator uses it.

iterator/iter_utils.c

@@ -161,8 +161,10 @@ iter_filter_unsuitable(struct iter_env* iter_env, struct module_env* env,
 	if(infra_get_lame_rtt(env->infra_cache, &a->addr, a->addrlen, 
 		name, namelen, &lame, &rtt, now)) {
 		if(lame)
-			return -1;
-		else 	return rtt;
+			return -1; /* server is lame */
+		else if(rtt >= USEFUL_SERVER_TOP_TIMEOUT)
+			return -1; /* server is unresponsive */
+		else	return rtt;
 	}
 	/* no server information present */
 	return UNKNOWN_SERVER_NICENESS;

iterator/iterator.h

@@ -53,8 +53,15 @@ struct iter_prep_list;
 #define MAX_RESTART_COUNT       8
 /** max number of referrals. Makes sure resolver does not run away */
 #define MAX_REFERRAL_COUNT	30
-/** how nice is a server without further information, in msec */
+/** how nice is a server without further information, in msec 
+ * Equals rtt initial timeout value.
+ */
 #define UNKNOWN_SERVER_NICENESS 3000
+/** maximum timeout before a host is deemed unsuitable, in msec. 
+ * After host_ttl this will be timed out and the host will be tried again. 
+ * Equals RTT_MAX_TIMEOUT
+ */
+#define USEFUL_SERVER_TOP_TIMEOUT	120000
 
 /**
  * Global state for the iterator.