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Creating a Blacklistd Ruleset
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The group and rule number of the rule in the format <literal>@0:17</literal>.
The action: <literal>p</literal> for passed, <literal>b</literal> for blocked, <literal>S</literal> for a short packet, <literal>n</literal> did not match any rules, and <literal>L</literal> for a log rule.
The addresses written as three fields: the source address and port separated by a comma, the -&gt; symbol, and the destination address and port. For example: <literal>209.53.17.22,80 -&gt; 198.73.220.17,1722</literal>.
<literal>PR</literal> followed by the protocol name or number: for example, <literal>PR tcp</literal>.
<literal>len</literal> followed by the header length and total length of the packet: for example, <literal>len 20 40</literal>.
If the packet is a <acronym>TCP</acronym> packet, there will be an additional field starting with a hyphen followed by letters corresponding to any flags that were set. Refer to <citerefentry><refentrytitle>ipf</refentrytitle><manvolnum>5</manvolnum></citerefentry> for a list of letters and their flags.
If the packet is an <acronym>ICMP</acronym> packet, there will be two fields at the end: the first always being <quote>icmp</quote> and the next being the <acronym>ICMP</acronym> message and sub-message type, separated by a slash. For example: <literal>icmp 3/3</literal> for a port unreachable message.
Blacklistd
Blacklistd is a daemon listening to sockets to receive notifications from other daemons about connection attempts that failed or were successful. It is most widely used in blocking too many connection attempts on open ports. A prime example is <application>SSH</application> running on the internet getting a lot of requests from bots or scripts trying to guess passwords and gain access. Using <application>blacklistd</application>, 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. FreeBSD 11 imported blacklistd from NetBSD.
This chapter describes how to set up blacklistd, configure it, and provides examples on how to use it. Readers should be familiar with basic firewall concepts like rules. For details, refer to the firewall chapter. PF is used in the examples, but other firewalls available on FreeBSD should be able to work with blacklistd, too.
Enabling Blacklistd
The main configuration for blacklistd is stored in <citerefentry><refentrytitle>blacklistd.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>. Various command line options are also available to change blacklistd's run-time behavior. Persistent configuration across reboots should be stored in <filename>/etc/blacklistd.conf</filename>. To enable the daemon during system boot, add a <literal>blacklistd_enable</literal> line to <filename>/etc/rc.conf</filename> like this:
<prompt>#</prompt> <userinput>sysrc blacklistd_enable=yes</userinput>
To start the service manually, run this command:
<prompt>#</prompt> <userinput>service blacklistd start</userinput>
Creating a Blacklistd Ruleset
Rules for blacklistd are configured in <citerefentry><refentrytitle>blacklistd.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry> with one entry per line. Each rule contains a tuple separated by spaces or tabs. Rules either belong to a <literal>local</literal> or a <literal>remote</literal>, which applies to the machine where blacklistd is running or an outside source, respectively.
Local Rules
An example blacklistd.conf entry for a local rule looks like this:
[local]
ssh stream * * * 3 24h
All rules that follow the <literal>[local]</literal> section are treated as local rules (which is the default), applying to the local machine. When a <literal>[remote]</literal> section is encountered, all rules that follow it are handled as remote machine rules.
Seven fields define a rule separated by either tabs or spaces. The first four fields identify the traffic that should be blacklisted. The three fields that follow define backlistd's behavior. Wildcards are denoted as asterisks (<literal>*</literal>), matching anything in this field. The first field defines the location. In local rules, these are the network ports. The syntax for the location field is as follows:
[<replaceable>address</replaceable>|<replaceable>interface</replaceable>][/<replaceable>mask</replaceable>][:<replaceable>port</replaceable>]
Adressses can be specified as IPv4 in numeric format or IPv6 in square brackets. An interface name like <literal><replaceable>em0</replaceable></literal> can also be used.
The socket type is defined by the second field. TCP sockets are of type <literal>stream</literal>, whereas UDP is denoted as <literal>dgram</literal>. The example above uses TCP, since SSH is using that protocol.
A protocol can be used in the third field of a blacklistd rule. The following protocols can be used: <literal>tcp</literal>, <literal>udp</literal>, <literal>tcp6</literal>, <literal>udp6</literal>, or numeric. 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.
In the fourth field, the effective user or owner of the daemon process that is reporting the event is defined. The username or <acronym>UID</acronym> can be used here, as well as a wildcard (see example rule above).
The packet filter rule name is declared by the fifth field, which starts the behavior part of the rule. By default, blacklistd puts all blocks under a pf anchor called <literal>blacklistd</literal> in <filename>pf.conf</filename> like this:
anchor "blacklistd/*" in on $ext_if
block in
pass out
For separate blacklists, an anchor name can be used in this field. In other cases, the wildcard will suffice. When a name starts with a hyphen (<literal>-</literal>) it means that an anchor with the default rule name prepended should be used. A modified example from the above using the hyphen would look like this:
ssh stream * * -ssh 3 24h

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Source string comment
(itstool) path: sect2/title
Source string location
book.translate.xml:63751
String age
8 months ago
Source string age
a year ago
Translation file
books/tr_TR/handbook.po, string 10445