arm: add why when to set 'require-server-cookie yes;'

(cherry picked from commit c5453ea3283d4326116955a24cc0cd18397a5ebb)

diff --git a/doc/arm/Bv9ARM-book.xml b/doc/arm/Bv9ARM-book.xml
index 9445c81e10a88ad24da9cdb416e1c5ca7afe6dea..7b5e0ddf1595996e5e323c8af87acf79f3c3fcda 100644 (file)
--- a/doc/arm/Bv9ARM-book.xml
+++ b/doc/arm/Bv9ARM-book.xml
@@ -6042,6 +6042,12 @@ options {
                  server cookie.
                  The default is <userinput>no</userinput>.
                </para>
+               <para>
+                 Set this to <userinput>yes</userinput> to test that DNS
+                 COOKIE clients correctly handle BADCOOKIE or if you are
+                 getting a lot of forged DNS requests with DNS COOKIES
+                 present.
+               </para>
              </listitem>
            </varlistentry>