When we have authoritative NS records in cache that do not lead to

any usable address, wipe the NS records so a query of NS records
to theprant leads to new NS records being inserted into the cache.

Previously the presence of the authoritaivbe records would prevent
that to happen. Queries would *use* the freshly retrieved parent
records, but they would not end up in the cache (the presence of
authoritative NS records prevents that) leading to repeated queries
to the parent.

diff --git a/pdns/recursordist/syncres.cc b/pdns/recursordist/syncres.cc
index 0e4822bedeecfc64bd6ce4a2fc6055f588287d67..26c38214d708a3f36af30e0c94bce54c04d3c621 100644 (file)
--- a/pdns/recursordist/syncres.cc
+++ b/pdns/recursordist/syncres.cc
@@ -2233,7 +2233,7 @@ void SyncRes::getBestNSFromCache(const DNSName& qname, const QType qtype, vector
     vector<DNSRecord> ns;
     *flawedNSSet = false;
 
-    if (g_recCache->get(d_now.tv_sec, subdomain, QType::NS, flags, &ns, d_cacheRemote, d_routingTag) > 0) {
+    if (bool isAuth = false; g_recCache->get(d_now.tv_sec, subdomain, QType::NS, flags, &ns, d_cacheRemote, d_routingTag, nullptr, nullptr, nullptr, nullptr, &isAuth) > 0) {
       if (s_maxnsperresolve > 0 && ns.size() > s_maxnsperresolve) {
         vector<DNSRecord> selected;
         selected.reserve(s_maxnsperresolve);
@@ -2269,10 +2269,15 @@ void SyncRes::getBestNSFromCache(const DNSName& qname, const QType qtype, vector
           else {
             *flawedNSSet = true;
             LOG(prefix << qname << ": NS in cache for '" << subdomain << "', but needs glue (" << nrr->getNS() << ") which we miss or is expired" << endl);
-            g_recCache->doWipeCache(subdomain, false, QType::NS);
           }
         }
       }
+      if (*flawedNSSet && bestns.empty() && isAuth) {
+        // The authoritative (child) NS records did not produce any usable addresses, wipe them, so
+        // these useless records do not prevent parent records to be inserted into the cache
+        LOG(prefix << qname << ": Wiping flawed authoritative NS records for " << subdomain << endl);
+        g_recCache->doWipeCache(subdomain, false, QType::NS);
+      }
 
       if (!bestns.empty()) {
         GetBestNSAnswer answer;