diff --git a/docs/images/Network2008a.dia b/docs/images/Network2008a.dia
index 381610279..5d549f510 100644
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diff --git a/docs/images/Network2008a.png b/docs/images/Network2008a.png
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diff --git a/docs/ipsets.xml b/docs/ipsets.xml
index d1cd4db60..2bc6934b2 100644
--- a/docs/ipsets.xml
+++ b/docs/ipsets.xml
@@ -76,6 +76,20 @@
 
     <para>Example: "+Mirrors"</para>
 
+    <para>When using Shorewall-perl, the names of ipsets are restricted as
+    follows:</para>
+
+    <itemizedlist>
+      <listitem>
+        <para>They must begin with a letter (after the '+').</para>
+      </listitem>
+
+      <listitem>
+        <para>They must be composed of letters, digits or underscores
+        ("_").</para>
+      </listitem>
+    </itemizedlist>
+
     <para>The name of the set may optionally followed by:</para>
 
     <orderedlist numeration="loweralpha">
@@ -214,4 +228,4 @@ dyn           eth3:+Dyn</programlisting>
     you're all set. You can add and delete addresses from Dyn without having
     to touch Shorewall.</para>
   </section>
-</article>
+</article>
\ No newline at end of file