Comments on config files and jails.

README.md

@@ -3,14 +3,18 @@
 ## Overview
 
 This is a basic set up for Fail2Ban on an system that is directly exposed to the
-internet (i.e. not behind a separate firewall).  In addition to the standard
+internet (i.e. not behind a separate firewall).
-SSHd jail, a separate jail that monitors UFW BLOCK reports (i.e. connection
+
-attempts to closed ports, etc.) is activated.  This should aid in blocking
+**This set-up assumes you are using UFW as your firewall front-end and it's
-'scriptkiddies' and port-scanning attacks, reducing the resources your server
+working correctly.**
-has to allocate to processing bogus requests.  F2B will automatically create UFW
+
-rules to drop connections from systems that try to make repeated invalid
+In addition to the standard SSHd jail, a separate jail that monitors UFW BLOCK
-connection attempts and then remove the block automatically after the 'bantime'
+reports (i.e. connection attempts to closed ports, etc.) is activated.  This
-has expired.
+should aid in blocking 'scriptkiddies' and port-scanning attacks, reducing the
+resources your server has to allocate to processing bogus requests.  F2B will
+automatically create UFW rules to drop connections from systems that try to make
+repeated invalid connection attempts and then remove the block automatically
+after the 'bantime' has expired.
 
 ## Installing an up-to-date Fail2Ban version
 
@@ -69,3 +73,220 @@ newer version from the source at github.
 
 ## Customizing your set up
 
+As with all Fail2Ban setups, you should do all your customization in the
+*.local* files and not the .conf files since those may be overwritten by
+updates.
+
+### /etc/fail2ban/fail2ban.conf
+
+I recommend reviewing your the following settings at a minimum for any
+deployment:
+
+#### loglevel
+This sets the verbosity of the log output from F2B.  The default setting of INFO
+is appropriate for most installs but, you should specify it anyways so you have
+any easy place to change it if you need to do so.
+
+```Ini
+loglevel = INFO
+```
+
+#### logtarget
+This controls the location of the F2B log file where it logs it's own actions.
+This is NOT the location of the log files it reads for banning!  Again, the
+default is appropriate for most installs, but you should specify it in your
+custom configuration so you have an easy place to change it if needed.
+
+```Ini
+logtarget = /var/log/fail2ban.log
+```
+
+#### dbpurgeage
+This controls how long F2B keeps a record of systems it has banned for whatever
+reason.  By default, this is set to one day. I prefer having a one week record
+so I can go back and review as necessary.  You can set it to whatever you want,
+duration is expressed in *seconds*.
+
+```Ini
+dbpurgeage = 604800
+```
+
+### /etc/fail2ban/jail.local
+
+This file overrides the defaults applied to all jail configurations used by F2B.
+This sets things like the default amount of time a system is banned, what
+actions should be used for banning systems and whether or not you get email
+notifications, etc.
+
+#### ignoreip
+
+This setting tells F2B which IP addresses/ranges/hostnames should **never** be
+banned.  In general, this should be the localhost only.  However, if you connect
+by remote using a particular machine, you might want to exempt it from any
+possible bans also.  You can specify more than one entry by separating them with
+a space or comma.  In this case, I've added the IP4 and IP6 defintions for localhost.
+
+```Ini
+ignoreip = 127.0.0.1/8 ::1
+```
+
+#### Timeframes
+
+You should customize the relevant timeframes to your requirements and this will
+likely take a little experimentation.  F2B checks for a system making '*maxretry*'
+failed attempts to connect or login within '*findtime*' seconds and, if that
+happens, bans the system for '*bantime*' seconds.
+
+I like using settings as below which state, "ban any system for 30 minutes that
+makes 5 invalid connection attempts within a 5 minute period".
+
+```Ini
+bantime = 1800
+maxretry = 5
+findtime = 300
+```
+
+Some people find this too aggressive and prefer settings such as 10 attempts in
+20 minutes, for example, which would look like:
+
+```Ini
+bantime = 1800
+maxretry = 10
+findtime = 1200
+```
+
+Again, this will be up to you to determine what is appropriate for your
+environment and users.  Remember that invididual jails can override these
+defaults.
+
+#### Actions
+
+##### Notication options
+
+If you choose actions that involve sending email notifications, you need to let
+F2B know where to send those emails and who should send them.  It's pretty
+straightforward, so this is the general setup:
+
+```Ini
+destemail = account@domain.tld
+sender = thismachine@domain.tld
+mta = sendmail
+```
+
+The '*mta*' field is very likely correct for your system, but if you are using a
+different MTA, you'll want to specify that here.
+
+##### Shortcuts
+
+This is where you tell F2B what exactly to do when it finds a reason to ban a
+system based on the jail configuration.  Again, individual jails can override
+these settings.  The settings are defined backwards in this file, so I'll take a
+second to explain.
+
+'*action*' is performed each time a system should be banned.  There are several
+predefined actions listed in the /etc/fail2ban/jail.conf file which you can use
+and are often sufficient for most setups.  Read the comments in that file to
+understand what each predefined action does.  In my case, I like getting an
+email along with a few lines from the log telling me what they did to get
+banned.
+
+Within '*action*' is '*banaction*' which is a link over to a specific
+configuration file telling F2B what to do on the system to enforce the ban.  In
+this setup, we direct F2B to look at the ufw.conf file to see how to modify
+UFW's rules so it drops packets from the offending system.  Details on that file are found later in this document.
+
+The general setup as described above is as follows:
+
+```Ini
+banaction = ufw
+action = %(action_mwl)s
+```
+
+## Jails
+
+F2B uses '*jail configurations*' specified either in */etc/fail2ban/jail.conf*,
+*/etc/fail2ban/jail.local* or in */etc/fail2ban/jail.d/*.  The latter is my
+preference since it allows for each jail to be contained in it's own
+configuration file which makes debugging and maintaining them much easier.
+
+### sshd (/etc/fail2ban/jail.d/ssh.conf)
+I usually just define a jail for *sshd* which is the SSH server.  You can add
+additional SSH jails as you wish to this file, but I keep it pretty simple.  One
+note, I run my SSH server on a non-standard port, so be sure you fill in the
+correct port for your environment such as my example below of port 222:
+
+```Ini
+[sshd]
+port    = 222
+...
+```
+
+If you are running on the standard port 22, then you can actually omit this line
+entirely since it's already defined in the default .conf files.  Also note that
+if you have customized your SSHd configuration to use non-standard logging,
+you'll want to specify a logfile location in the jail also, like this:
+
+```Ini
+[sshd]
+...
+logpath     = /path/to/your/log.file
+...
+```
+
+### UFW port probing
+
+This is probably the what you are really looking for in this entire set-up.  We
+will create a custom jail that monitors UFW's logs for any mention of *[UFW
+BLOCK]* and then proceeds to ban those systems attempting to connect to blocked
+ports as per your timeframe settings.  I've commented the ufw-probe file but
+I'll run though it here also for convenience.
+
+#### Name of the jail
+
+You can call this anything that has meaning to you, I've chosen '*ufw-probe*'.
+Just change what it says in the [square brackets]
+
+```Ini
+[ufw-probe]
+...
+```
+
+#### Ports and IPs
+
+Since this is searching for port probing, we will tell F2B to look for attempts
+made to connect to any and all ports.  **The '*ignoreip*' parameter is only
+necessary IF it's different from what you've already set in '*jail.local*'.**
+
+```Ini
+port        = all
+ignoreip    = 127.0.0.1/8 ::1
+```
+
+#### Timeframes
+
+This section is also optional and is only needed if it's different from what you
+have in your '*jail.local*'.  I like keeping it in this configuration file
+though since the settings for this jail are often different from others.
+
+```Ini
+maxretry    = 5
+findtime    = 300
+```
+
+#### Jail-specific settings
+
+In order for this jail to function, you need to give F2B a little information.
+First, we need to specify what log file it should be parsing.  In this case,
+it's the UFW log file which is, by default, located at */var/log/ufw.log*.  If
+you've changed this, then update the '*logpath*' parameter.  We also need to
+tell it what filter to use when parsing the file, in this case, it's a filter
+I've called 'ufw-probe' (change this if you change the filename) which is
+located at */etc/fail2ban/filter.d/ufw-probe.conf* [details here].  Finally, we
+tell F2B to enable this jail.
+
+```Ini
+logpath     = /var/log/ufw.log
+filter      = ufw-probe
+enabled     = true
+```
+