<b><a name="description">DESCRIPTION</a></b>
The Postfix mail system uses optional lookup tables. These tables are
usually in <b><a href="lmdb_table.5.html">lmdb</a>:</b>, <b><a href="CDB_README.html">cdb</a>:</b>, <b><ahref="DATABASE_README.html#types">hash</a>:</b>, or <b><a href="DATABASE_README.html#types">dbm</a>:</b> format.
Alternatively, lookup tables can be specified in CIDR (Classless
Inter-Domain Routing) form. In this case, each input is compared
against a list of patterns. When a match is found, the corresponding
result is returned and the search is terminated.
To find out what types of lookup tables your Postfix system supports
use the "<b>postconf -m</b>"command.
To test lookup tables, use the "<b>postmap -q</b>"command as described in the
SYNOPSIS above.
<b><a name="table_format">TABLE FORMAT</a></b>
The general form of a Postfix CIDR table is:
<i>pattern result</i>
When a search string matches the specified <i>pattern</i>, use the cor-
responding <i>result</i> value. The <i>pattern</i> must be in <i>network/prefix</i>
or <i>network</i><b>_</b><i>address</i> form (see ADDRESS PATTERN SYNTAX below).
<b>!</b><i>pattern result</i>
When a search string does not match the specified <i>pattern</i>, use
the specified <i>result</i> value. The <i>pattern</i> must be in <i>network/pre-</i>
<i>fix</i> or <i>network</i><b>_</b><i>address</i> form (see ADDRESS PATTERN SYNTAX below).
This feature is available in Postfix 3.2 and later.
<b>if</b> <i>pattern</i>
<b>endif</b> When a search string matches the specified <i>pattern</i>, match that
search string against the patterns between <b>if</b> and <b>endif</b>. The
<i>pattern</i> must be in <i>network/prefix</i> or <i>network</i><b>_</b><i>address</i> form (see
ADDRESS PATTERN SYNTAX below). The <b>if</b>..<b>endif</b> can nest.
Note: do not prepend whitespace to text between <b>if</b>..<b>endif</b>.
This feature is available in Postfix 3.2 and later.
<b>if !</b><i>pattern</i>
<b>endif</b> When a search string does not match the specified <i>pattern</i>, match
that search string against the patterns between <b>if</b> and <b>endif</b>.
The <i>pattern</i> must be in <i>network/prefix</i> or <i>network</i><b>_</b><i>address</i> form
(see ADDRESS PATTERN SYNTAX below). The <b>if</b>..<b>endif</b> can nest.
Note: do not prepend whitespace to text between <b>if</b>..<b>endif</b>.
This feature is available in Postfix 3.2 and later.
blank lines and comments
Empty lines and whitespace-only lines are ignored, as are lines
whose first non-whitespace character is a `#'.
multi-line text
A logical line starts with non-whitespace text. A line that
starts with whitespace continues a logical line.
<b><a name="table_search_order">TABLE SEARCH ORDER</a></b>
Patterns are applied in the order as specified in the table, until a
pattern is found that matches the search string.
<b><a name="address_pattern_syntax">ADDRESS PATTERN SYNTAX</a></b>
Postfix CIDR tables are pattern-based. A pattern is either a <i>net-</i>
<i>work</i><b>_</b><i>address</i> which requires an exact match, or a <i>network</i><b>_</b><i>address/pre-</i>
<i>fix</i><b>_</b><i>length</i> where the <i>prefix</i><b>_</b><i>length</i> part specifies the length of the
<i>network</i><b>_</b><i>address</i> prefix that must be matched (the other bits in the <i>net-</i>
<i>work</i><b>_</b><i>address</i> part must be zero).
An IPv4 network address is a sequence of four decimal octets separated
by ".", and an IPv6 network address is a sequence of three to eight
hexadecimal octet pairs separated by ":" or "::", where the latter is
short-hand for a sequence of one or more all-zero octet pairs. The pat-
tern 0.0.0.0/0 matches every IPv4 address, and ::/0 matches every IPv6 address. IPv6 support is available in Postfix 2.2 and later.
Before comparisons are made, lookup keys and table entries are con-
verted from string to binary. Therefore, IPv6 patterns will be matched
regardless of leading zeros (a leading zero in an IPv4 address octet
indicates octal notation).
Note: address information may be enclosed inside "[]" but this form is
not required.
<b><a name="inline_specification">INLINE SPECIFICATION</a></b>
The contents of atable may be specified in the table name (Postfix 3.7
and later). The basic syntax is:
Postfix recursively expands any <i>$parametername</i> instances in the above
parameter value, ignores whitespace after '{' and before '}', and
writes each <i>rule</i> as one text line to an in-memory file:
in-memory file:
rule-1
rule-2
..
Postfix parses the result as if it is a file in /etc/postfix.
Note: if a rule contains <b>$</b>, specify <b>$$</b> to keep Postfix from trying to
do <i>$name</i> expansion as it evaluates a parameter value.
/etc/postfix/client.<a href="cidr_table.5.html">cidr</a>:
# Rule order matters. Put more specific allowlist entries
# before more general denylist entries. 192.168.1.1 OK 192.168.0.0/16 REJECT 2001:db8::1 OK 2001:db8::/32 REJECT
<b><a name="see_also">SEE ALSO</a></b>
<a href="postmap.1.html">postmap(1)</a>, Postfix lookup table manager
<a href="regexp_table.5.html">regexp_table(5)</a>, format of regular expression tables
<a href="pcre_table.5.html">pcre_table(5)</a>, format of PCRE tables
<b><a name="history">HISTORY</a></b>
CIDR table support was introduced with Postfix version 2.1.
<b>AUTHOR(S)</b>
The CIDR table lookup code was originally written by:
Jozsef Kadlecsik
KFKI Research Institute for Particle and Nuclear Physics
POB. 49 1525 Budapest, Hungary
Adopted and adapted by:
Wietse Venema
IBM T.J. Watson Research
P.O. Box 704
Yorktown Heights, NY 10598, USA
Wietse Venema
Google, Inc. 1118th Avenue
New York, NY 10011, USA
CIDR_TABLE(5)
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