[#181] add note about flex-id use in IPv6 PXE boot

diff --git a/doc/sphinx/arm/hooks-flex-id.rst b/doc/sphinx/arm/hooks-flex-id.rst
index 0cb7c60395b4a043df3e11e1b98408917bc84d88..d485f0b4a81b14562cb0a66fd46c1a931e1d7dcd 100644 (file)
--- a/doc/sphinx/arm/hooks-flex-id.rst
+++ b/doc/sphinx/arm/hooks-flex-id.rst
@@ -156,6 +156,12 @@ for non-printable characters and do not require the use of the
        ...
    }
 
+.. note::
+
+    One less common scenario where the examples above may prove useful is for
+    DHCPv6 clients that change their DUIDs between exchanges. Certain PXE
+    clients are known to behave this way.
+
 The ``replace-client-id`` Flag
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~