cidr_table − format of Postfix CIDR tables


postmap -q "string" cidr:/etc/postfix/filename

postmap -q - cidr:/etc/postfix/filename <inputfile


The Postfix mail system uses optional lookup tables. These tables are usually in dbm or db 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 "postconf -m" command.

To test lookup tables, use the "postmap -q" command as described in the SYNOPSIS above.


The general form of a Postfix CIDR table is:
/network_mask result

When a search string matches the specified network block, use the corresponding result value. Specify to match every IPv4 address, and ::/0 to match every IPv6 address.

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 ":".

The network_mask is the number of high-order bits in the network_address that the search string must match.

Before comparisons are made, lookup keys and table entries are converted from string to binary. Therefore table entries will be matched regardless of redundant zero characters.

Note: address information may be enclosed inside "[]" but this form is not required.

IPv6 support is available in Postfix 2.2 and later.

network_address result

When a search string matches the specified network address, use the corresponding result value.

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.


Patterns are applied in the order as specified in the table, until a pattern is found that matches the search string.


smtpd_client_restrictions = ... cidr:/etc/postfix/client.cidr ...

# Rule order matters. Put more specific whitelist entries
# before more general blacklist entries. OK REJECT


postmap(1), Postfix lookup table manager
regexp_table(5), format of regular expression tables
pcre_table(5), format of PCRE tables


Use "postconf readme_directory" or "postconf html_directory" to locate this information.
DATABASE_README, Postfix lookup table overview


CIDR table support was introduced with Postfix version 2.1.


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


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