From 682f8ffdd7cd71b77277719b114d4ca813175da4 Mon Sep 17 00:00:00 2001
From: Christian Poessinger <christian@poessinger.com>
Date: Mon, 21 May 2018 11:47:17 +0200
Subject: T588: Configurable Negative TTL caching in forwarder

---
 interface-definitions/dns-forwarding.xml | 14 ++++++++++++--
 src/conf_mode/dns_forwarding.py          | 10 +++++++++-
 2 files changed, 21 insertions(+), 3 deletions(-)

diff --git a/interface-definitions/dns-forwarding.xml b/interface-definitions/dns-forwarding.xml
index 273d7777b..5b69ecc81 100644
--- a/interface-definitions/dns-forwarding.xml
+++ b/interface-definitions/dns-forwarding.xml
@@ -1,7 +1,5 @@
 <?xml version="1.0"?>
-
 <!-- DNS forwarder configuration -->
-
 <interfaceDefinition>
   <node name="service">
     <children>
@@ -92,6 +90,18 @@
                   <multi/>
                 </properties>
               </leafNode>
+              <leafNode name="negative-ttl">
+                <properties>
+                  <help>Maximum amount of time negative entries are cached</help>
+                  <valueHelp>
+                    <format>0-7200</format>
+                    <description>Seconds to cache NXDOMAIN entries</description>
+                  </valueHelp>
+                  <constraint>
+                    <validator name="numeric" argument="--range 0-7200"/>
+                  </constraint>
+                </properties>
+              </leafNode>
               <leafNode name="name-server">
                 <properties>
                   <help>Domain Name Server (DNS)</help>
diff --git a/src/conf_mode/dns_forwarding.py b/src/conf_mode/dns_forwarding.py
index a04726da0..f5ad2e482 100755
--- a/src/conf_mode/dns_forwarding.py
+++ b/src/conf_mode/dns_forwarding.py
@@ -43,6 +43,9 @@ non-local-bind=yes
 # cache-size
 max-cache-entries={{ cache_size }}
 
+# negative TTL for NXDOMAIN
+max-negative-ttl={{ negative_ttl }}
+
 # ignore-hosts-file
 export-etc-hosts={{ export_hosts_file }}
 
@@ -65,11 +68,12 @@ forward-zones-recurse=.={{ name_servers | join(';') }}
 """
 
 default_config_data = {
-    'cache_size' : 10000,
+    'cache_size': 10000,
     'export_hosts_file': 'yes',
     'listen_on': [],
     'interfaces': [],
     'name_servers': [],
+    'negative_ttl': 3600,
     'domains': []
 }
 
@@ -100,6 +104,10 @@ def get_config():
         cache_size = conf.return_value('cache-size')
         dns['cache_size'] = cache_size
 
+    if conf.exists('negative-ttl'):
+        negative_ttl = conf.return_value('negative-ttl')
+        dns['negative_ttl'] = negative_ttl
+
     if conf.exists('domain'):
         for node in conf.list_nodes('domain'):
             server = conf.return_values("domain {0} server".format(node))
-- 
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