diff --git a/README.md b/README.md
index 20e44cb..0d3f543 100644
--- a/README.md
+++ b/README.md
@@ -214,3 +214,39 @@ if (strpos($_SERVER['HTTP_X_FORWARDED_PROTO'], 'https') !== false)
    $_SERVER['HTTPS']='on';
 ```
 
+
+### DNS Server Tests
+
+```bash
+root@moby:~# cat /etc/cron.d/checkdnsserver 
+#
+# Check DNS Server
+#
+*/15 * * * * root /usr/local/bin/checkdnsserver.sh >/dev/null
+
+
+root@moby:~# cat /usr/local/bin/checkdnsserver.sh
+#!/bin/bash
+# 
+# Check my DNS servers and report to CloudRadar
+#
+# Joerg Lehmann, 17.8.2021
+#
+
+for dnsserver in ns1.nbit.ch ns2.nbit.ch ; do
+  dig +short ${dnsserver} @${dnsserver} >/dev/null 2>&1
+  if [ $? -eq 0 ]; then
+    csender -t 6tZlIPoM7OQb \
+      -u https://hub.cloudradar.io/cct/ \
+      -n checkdnsserver \
+      -s 1
+  else
+    csender -t 6tZlIPoM7OQb \
+      -u https://hub.cloudradar.io/cct/ \
+      -n checkdnsserver \
+      -s 0 \
+      -a "DNS Test @${dnsserver} failed"
+  fi
+  sleep 10
+done
+```