diff --git a/books/portable-docker.org b/books/portable-docker.org
index 4ff0f938f..66c0d0496 100644
--- a/books/portable-docker.org
+++ b/books/portable-docker.org
@@ -309,6 +309,22 @@ on) to visit your pages.
 
 [[/img/portable-docker/hello-traefik.webp]]
 
+#+begin_mermaid
+---
+title: A web browser must query DNS before it can fetch any web page
+---
+sequenceDiagram
+participant Browser as Web Browser
+participant DNS as DNS Server
+participant WEB as Web Server
+
+    Browser->>DNS: DNS Request (Resolve domain name)
+    DNS-->>Browser: DNS Response (IP Address)
+    Browser->>WEB: HTTP Request (Fetch Web Page)
+    WEB-->>Browser: HTTP Response (Web Page Content)
+#+end_mermaid
+
+
 *** Domain name registration
 
 The public domain name registration system is controlled as a scarce