doc: DNS Flag Day 2020 warning

diff --git a/doc/upgrading.rst b/doc/upgrading.rst
index e243bf9128b22c95beef114530050ef19bf7baba..c7222166dcfc0e126a85123d270360a89b1e87f4 100644 (file)
--- a/doc/upgrading.rst
+++ b/doc/upgrading.rst
@@ -17,9 +17,6 @@ Following section provides information about selected changes in not-yet-release
 We advise users to prepare for these changes sooner rather than later to make it easier to upgrade to
 newer versions when they are released.
 
-Users
------
-
 * Users of :ref:`control-sockets` API need to terminate each command sent to resolver with newline
   character (ASCII ``\n``). Correct usage: ``cache.stats()\n``.
   Newline terminated commands are accepted by all resolver versions >= 1.0.0.
@@ -32,6 +29,9 @@ Users
 * DoH served with http module :ref:`DNS-over-HTTP (DoH) <mod-http-doh>` will be marked as legacy
   and won't receive any more bugfixes. A more reliable and scalable DoH module will be available
   instead. The new DoH module will only support HTTP/2 over TLS.
+* New releases since Octomer 2020 will contain changes for
+  `DNS Flag Day 2020 <https://dnsflagday.net/2020/>`_. Please double-check your firewall,
+  it has to allow DNS traffic on UDP and also TCP port 53.
 
 5.0 to 5.1
 ==========