[#3252] hub-and-spoke/radius incompatibility

The subnet reselect in RADIUS is incompatible with the hub-and-spoke.
Added suitable notes in the ARM.

Author: msiodelski

doc/sphinx/arm/ext-radius.rst

@@ -388,6 +388,15 @@ other than Discover and the first Request from each client.
    than global. Loading the RADIUS hook library in a Kea DHCP server
    that has this configuration raises an error.
 
+.. note::
+
+    Currently the ``reselect-subnet-address`` and ``reselect-subnet-pool``
+    parameters are incompatible with the hub-and-spoke configuration of the
+    :ischooklib:`libdhcp_ha.so`. This hook library uses an originally
+    selected subnet for choosing an HA relationship to process a packet.
+    The subnet reslection may interefere with this choice. See the
+    :ref:`ha-hub-and-spoke` for details.
+
 .. _radius-server-example:
 
 RADIUS Server Setup Example

doc/sphinx/arm/hooks-ha.rst

@@ -2607,3 +2607,11 @@ branch ``server3``:
 
    The peer names in the branch servers must match the peer names in the respective central
    server's relationships, because these names are used for signaling between the HA partners.
+
+.. note::
+
+    The hub-and-spoke configuration is currently incompatible with the ``reselect-subnet-address``
+    and ``reselect-subnet-pool`` parameters of the :ischooklib:`libdhcp_radius.so`. The High
+    Availability hook library uses an originally selected subnet for choosing an HA relationship
+    to process a packet. The subnet reslection may interefere with this choice. See the
+    :ref:`radius-config` for details.