Retry send DNS response without extra section

nameserver/response.go

@@ -53,5 +53,14 @@ func writeDNSResponse(w dns.ResponseWriter, m *dns.Msg) (err error) {
 	}()
 
 	err = w.WriteMsg(m)
+	if err == nil {
+		// If we receive an error we might have exceeded the message size with all
+		// our extra information records. Retry again without the extra section.
+		m.Extra = nil
+		noExtraErr := w.WriteMsg(m)
+		if noExtraErr == nil {
+			log.Warningf("nameserver: failed to write dns message with extra section: %s", err)
+		}
+	}
 	return
 }