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@@ -4,7 +4,7 @@ part: IV. Network Communication
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prev: books/handbook/network-servers
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next: books/handbook/advanced-networking
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description: "FreeBSD has three firewalls built into the base system: PF, IPFW, and IPFILTER. This chapter covers how to define packet filtering rules, the differences between the firewalls built into FreeBSD and how to use them"
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If the packet is an ICMP packet, there will be two fields at the end: the first always being "icmp" and the next being the ICMP message and sub-message type, separated by a slash.
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For example: `icmp 3/3` for a port unreachable message.
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[[firewalls-blacklistd]]
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== Blacklistd
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[[firewalls-blocklistd]]
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== Blocklistd
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Blacklistd is a daemon listening to sockets awaiting to receive notifications from other daemons about connection attempts that failed or were successful.
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Blocklistd is a daemon listening to sockets awaiting to receive notifications from other daemons about connection attempts that failed or were successful.
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It is most widely used in blocking too many connection attempts on open ports.
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A prime example is SSH running on the internet getting a lot of requests from bots or scripts trying to guess passwords and gain access.
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Using blacklistd, the daemon can notify the firewall to create a filter rule to block excessive connection attempts from a single source after a number of tries. Blacklistd was first developed on NetBSD and appeared there in version 7.
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FreeBSD 11 imported blacklistd from NetBSD.
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Using blocklistd, the daemon can notify the firewall to create a filter rule to block excessive connection attempts from a single source after a number of tries. Blocklistd was first developed on NetBSD and appeared there in version 7, it was originally called blacklistd.
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FreeBSD 11 imported blocklistd from NetBSD.
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This chapter describes how to set up blacklistd, configure it, and provides examples on how to use it.
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This chapter describes how to set up blocklistd, configure it, and provides examples on how to use it.
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Readers should be familiar with basic firewall concepts like rules.
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For details, refer to the firewall chapter.
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PF is used in the examples, but other firewalls available on FreeBSD should be able to work with blacklistd, too.
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PF is used in the examples, but other firewalls available on FreeBSD should be able to work with blocklistd, too.
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=== Enabling Blacklistd
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=== Enabling Blocklistd
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The main configuration for blacklistd is stored in man:blacklistd.conf[5].
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Various command line options are also available to change blacklistd's run-time behavior.
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Persistent configuration across reboots should be stored in [.filename]#/etc/blacklistd.conf#.
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To enable the daemon during system boot, add a `blacklistd_enable` line to [.filename]#/etc/rc.conf# like this:
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The main configuration for blocklistd is stored in man:blocklistd.conf[5].
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Various command line options are also available to change blocklistd's run-time behavior.
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Persistent configuration across reboots should be stored in [.filename]#/etc/blocklistd.conf#.
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To enable the daemon during system boot, add a `blocklistd_enable` line to [.filename]#/etc/rc.conf# like this:
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[source,shell]
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....
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# sysrc blacklistd_enable=yes
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# sysrc blocklistd_enable=yes
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....
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To start the service manually, run this command:
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[source,shell]
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....
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# service blacklistd start
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# service blocklistd start
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....
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=== Creating a Blacklistd Ruleset
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=== Creating a Blocklistd Ruleset
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Rules for blacklistd are configured in man:blacklistd.conf[5] with one entry per line.
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Rules for blocklistd are configured in man:blocklistd.conf[5] with one entry per line.
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Each rule contains a tuple separated by spaces or tabs.
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Rules either belong to a `local` or a `remote`, which applies to the machine where blacklistd is running or an outside source, respectively.
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Rules either belong to a `local` or a `remote`, which applies to the machine where blocklistd is running or an outside source, respectively.
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==== Local Rules
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An example blacklistd.conf entry for a local rule looks like this:
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An example blocklistd.conf entry for a local rule looks like this:
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[.programlisting]
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....
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Seven fields separated by either tabs or spaces define a rule.
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The first four fields identify the traffic that should be blocklisted.
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The three fields that follow define backlistd's behavior.
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The three fields that follow define blocklistd's behavior.
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Wildcards are denoted as asterisks (`*`), matching anything in this field.
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The first field defines the location.
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In local rules, these are the network ports.
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TCP sockets are of type `stream`, whereas UDP is denoted as `dgram`.
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The example above uses TCP, since SSH is using that protocol.
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A protocol can be used in the third field of a blacklistd rule.
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A protocol can be used in the third field of a blocklistd rule.
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The following protocols can be used: `tcp`, `udp`, `tcp6`, `udp6`, or numeric.
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A wildcard, like in the example, is typically used to match all protocols unless there is a reason to distinguish traffic by a certain protocol.
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In the fourth field, the effective user or owner of the daemon process that is reporting the event is defined.
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The username or UID can be used here, as well as a wildcard (see example rule above).
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The packet filter rule name is declared by the fifth field, which starts the behavior part of the rule.
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By default, blacklistd puts all blocks under a pf anchor called `blacklistd` in [.filename]#pf.conf# like this:
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By default, blocklistd puts all blocks under a pf anchor called `blocklistd` in [.filename]#pf.conf# like this:
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[.programlisting]
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....
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anchor "blacklistd/*" in on $ext_if
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anchor "blocklistd/*" in on $ext_if
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block in
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pass out
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....
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ssh stream * * -ssh 3 24h
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....
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With such a rule, any new blocklist rules are added to an anchor called `blacklistd-ssh`.
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With such a rule, any new blocklist rules are added to an anchor called `blocklistd-ssh`.
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To block whole subnets for a single rule violation, a `/` in the rule name can be used.
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This causes the remaining portion of the name to be interpreted as the mask to be applied to the address specified in the rule.
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When a wildcard is used at this position, it means that blocks will never happen.
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In the example rule above, a limit of three is defined meaning that after three attempts to log into SSH on one connection, the IP is blocked.
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The last field in a blacklistd rule definition specifies how long a host is blocklisted.
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The last field in a blocklistd rule definition specifies how long a host is blocklisted.
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The default unit is seconds, but suffixes like `m`, `h`, and `d` can also be specified for minutes, hours, and days, respectively.
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The example rule in its entirety means that after three times authenticating to SSH will result in a new PF block rule for that host.
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Rule matches are performed by first checking local rules one after another, from most specific to least specific.
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When a match occurs, the `remote` rules are applied and the name, `nfail`, and disable fields are changed by the `remote` rule that matched.
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When a match occurs, the `remote` rules are applied and the `name`, `nfail`, and `duration` fields are changed by the `remote` rule that matched.
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==== Remote Rules
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Remote rules are used to specify how blacklistd changes its behavior depending on the remote host currently being evaluated.
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Remote rules are used to specify how blocklistd changes its behavior depending on the remote host currently being evaluated.
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Each field in a remote rule is the same as in a local rule.
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The only difference is in the way blacklistd is using them.
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The only difference is in the way blocklistd is using them.
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To explain it, this example rule is used:
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[.programlisting]
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This allows setting special rules for a specific remote address range like in this example.
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The fields for socket type, protocol and owner are identically interpreted as in the local rule.
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The name fields is different though: the equal sign (`=`) in a remote rule tells blacklistd to use the value from the matching local rule.
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The name fields is different though: the equal sign (`=`) in a remote rule tells blocklistd to use the value from the matching local rule.
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It means that the firewall rule entry is taken and the `/25` prefix (a netmask of `255.255.255.128`) is added.
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When a connection from that address range is blocklisted, the entire subnet is affected.
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A PF anchor name can also be used here, in which case blacklistd will add rules for this address block to the anchor of that name.
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A PF anchor name can also be used here, in which case blocklistd will add rules for this address block to the anchor of that name.
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The default table is used when a wildcard is specified.
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A custom number of failures in the `nfail` column can be defined for an address.
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Remote rules allow a stricter enforcement of limits on attempts to log in compared to attempts coming from a local network like an office.
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=== Blacklistd Client Configuration
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=== Blocklistd Client Configuration
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There are a few software packages in FreeBSD that can utilize blacklistd's functionality.
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There are a few software packages in FreeBSD that can utilize blocklistd's functionality.
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The two most prominent ones are man:ftpd[8] and man:sshd[8] to block excessive connection attempts.
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To activate blacklistd in the SSH daemon, add the following line to [.filename]#/etc/ssh/sshd_config#:
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To activate blocklistd in the SSH daemon, add the following line to [.filename]#/etc/ssh/sshd_config#:
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[.programlisting]
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UseBlacklist yes
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UseBlocklist yes
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....
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Restart sshd afterwards to make these changes take effect.
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Blacklisting for man:ftpd[8] is enabled using `-B`, either in [.filename]#/etc/inetd.conf# or as a flag in [.filename]#/etc/rc.conf# like this:
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Blocklisting for man:ftpd[8] is enabled using `-B`, either in [.filename]#/etc/inetd.conf# or as a flag in [.filename]#/etc/rc.conf# like this:
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[.programlisting]
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....
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ftpd_flags="-B"
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....
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That is all that is needed to make these programs talk to blacklistd.
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That is all that is needed to make these programs talk to blocklistd.
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=== Blacklistd Management
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=== Blocklistd Management
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Blacklistd provides the user with a management utility called man:blacklistctl[8].
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It displays blocked addresses and networks that are blocklisted by the rules defined in man:blacklistd.conf[5].
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Blocklistd provides the user with a management utility called man:blocklistctl[8].
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It displays blocked addresses and networks that are blocklisted by the rules defined in man:blocklistd.conf[5].
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To see the list of currently blocked hosts, use `dump` combined with `-b` like this.
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[source,shell]
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# blacklistctl dump -b
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address/ma:port id nfail last access
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213.0.123.128/25:22 OK 6/3 2019/06/08 14:30:19
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# blocklistctl dump -b
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rulename address/ma:port id nfail last access
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blocklistd 213.0.123.128/25:22 OK 6/3 2019/06/08 14:30:19
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This example shows that there were 6 out of three permitted attempts on port 22 coming from the address range `213.0.123.128/25`.
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There are more attempts listed than are allowed because SSH allows a client to try multiple logins on a single TCP connection.
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A connection that is currently going on is not stopped by blacklistd.
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A connection that is currently going on is not stopped by blocklistd.
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The last connection attempt is listed in the `last access` column of the output.
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To see the remaining time that this host will be on the blocklist, add `-r` to the previous command.
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[source,shell]
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# blacklistctl dump -br
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address/ma:port id nfail remaining time
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213.0.123.128/25:22 OK 6/3 36s
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# blocklistctl dump -br
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rulename address/ma:port id nfail remaining time
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blocklistd 213.0.123.128/25:22 OK 6/3 36s
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In this example, there are 36s seconds left until this host will not be blocked any more.
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=== Removing Hosts from the Block List
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Sometimes it is necessary to remove a host from the block list before the remaining time expires.
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Unfortunately, there is no functionality in blacklistd to do that.
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Unfortunately, there is no functionality in blocklistd to do that.
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However, it is possible to remove the address from the PF table using pfctl.
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For each blocked port, there is a child anchor inside the blacklistd anchor defined in [.filename]#/etc/pf.conf#.
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For example, if there is a child anchor for blocking port 22 it is called `blacklistd/22`.
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For each blocked port, there is a child anchor inside the blocklistd anchor defined in [.filename]#/etc/pf.conf#.
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For example, if there is a child anchor for blocking port 22 it is called `blocklistd/22`.
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There is a table inside that child anchor that contains the blocked addresses.
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This table is called port followed by the port number.
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In this example, it would be called `port22`.
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With that information at hand, it is now possible to use man:pfctl[8] to display all addresses listed like this:
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[source,shell]
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# pfctl -a blacklistd/22 -t port22 -T show
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# pfctl -a blocklistd/22 -t port22 -T show
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213.0.123.128/25
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[source,shell]
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# pfctl -a blacklistd/22 -t port22 -T delete 213.0.123.128/25
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# pfctl -a blocklistd/22 -t port22 -T delete 213.0.123.128/25
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....
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The address is now removed from PF, but will still show up in the blacklistctl list, since it does not know about any changes made in PF.
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The entry in blacklistd's database will eventually expire and be removed from its output.
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The entry will be added again if the host is matching one of the block rules in blacklistd again.
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The address is now removed from PF, but will still show up in the blocklistctl list, since it does not know about any changes made in PF.
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The entry in blocklistd's database will eventually expire and be removed from its output.
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The entry will be added again if the host is matching one of the block rules in blocklistd again.
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