diff --git a/ex-1_iptables.adoc b/ex-1_iptables.adoc
index 455bd95..3f6ee04 100644
--- a/ex-1_iptables.adoc
+++ b/ex-1_iptables.adoc
@@ -95,6 +95,7 @@ testnetwork2_worker_2.testnetwork2_net (172.21.0.6)
 [NOTE]
 ====
 Nmap, short for Network Mapper, is a free, open-source tool for vulnerability scanning and network discovery. Network administrators use Nmap to identify what devices are running on their systems, discovering hosts that are available and the services they offer, finding open ports and detecting security risks.
+See https://en.wikipedia.org/wiki/Nmap
 ====