Update fail2ban documentation

docs/faq.rst

@@ -528,25 +528,42 @@ The above will block flagged IPs for a week, you can of course change it to you
   
   actionstart = iptables -N f2b-bad-auth
                 iptables -A f2b-bad-auth -j RETURN
-                iptables -I FORWARD -p tcp -m multiport --dports 1:1024 -j f2b-bad-auth
+                iptables -I DOCKER-USER -p tcp -m multiport --dports 1:1024 -j f2b-bad-auth
   
-  actionstop = iptables -D FORWARD -p tcp -m multiport --dports 1:1024 -j f2b-bad-auth
+  actionstop = iptables -D DOCKER-USER -p tcp -m multiport --dports 1:1024 -j f2b-bad-auth
                iptables -F f2b-bad-auth
                iptables -X f2b-bad-auth
   
-  actioncheck = iptables -n -L FORWARD | grep -q 'f2b-bad-auth[ \t]'
+  actioncheck = iptables -n -L DOCKER-USER | grep -q 'f2b-bad-auth[ \t]'
   
   actionban = iptables -I f2b-bad-auth 1 -s <ip> -j DROP
   
   actionunban = iptables -D f2b-bad-auth -s <ip> -j DROP
 
-5. Restart Fail2Ban
+Using DOCKER-USER chain ensures that blocked IPs are processed in correct order with Docker. See more in: https://docs.docker.com/network/iptables/
+
+5. Configure and restart Fail2Ban service
+
+Make sure Fail2Ban is started after Docker service by adding partial override which appends this to existing configuration..
+
+.. code-block:: bash
+
+  sudo systemctl edit fail2ban
+
+Add override and save file.
+
+.. code-block:: bash
+
+  [Unit]
+  After=docker.service
+
+Restart service.
 
 .. code-block:: bash
 
   sudo systemctl restart fail2ban
 
-*Issue reference:* `85`_, `116`_, `171`_, `584`_, `592`_.
+*Issue reference:* `85`_, `116`_, `171`_, `584`_, `592`_, `1727`_.
 
 Users can't change their password from webmail
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@@ -670,7 +687,7 @@ iptables -t nat -A POSTROUTING -o eth0 -p tcp --dport 25 -j SNAT --to <your mx i
 .. _`1090`: https://github.com/Mailu/Mailu/issues/1090
 .. _`unbound`: https://nlnetlabs.nl/projects/unbound/about/
 .. _`1438`: https://github.com/Mailu/Mailu/issues/1438
-
+.. _`1727`: https://github.com/Mailu/Mailu/issues/1727
 
 A user gets ``Sender address rejected: Access denied. Please check the`` ``message recipient […] and try again`` even though the sender is legitimate?
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