Postfix manual - cidr_table(5)

    CIDR_TABLE(5)                                                    CIDR_TABLE(5)

    NAME
           cidr_table - format of Postfix CIDR tables

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

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

    DESCRIPTION
           The  Postfix mail system uses optional lookup tables.  These tables are
           usually in lmdb:, cdb:, hash:, or dbm: 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.

    TABLE FORMAT
           The general form of a Postfix CIDR table is:

           pattern     result
                  When a search string matches the specified pattern, use the cor-
                  responding result value. The pattern must be  in  network/prefix
                  or network_address form (see ADDRESS PATTERN SYNTAX below).

           !pattern     result
                  When  a  search string does not match the specified pattern, use
                  the specified result value. The pattern must be in  network/pre-
                  fix  or network_address form (see ADDRESS PATTERN SYNTAX below).

                  This feature is available in Postfix 3.2 and later.

           if pattern

           endif  When a search string matches the specified pattern,  match  that
                  search  string  against  the patterns between if and endif.  The
                  pattern must be in network/prefix or network_address  form  (see
                  ADDRESS PATTERN SYNTAX below). The if..endif can nest.

                  Note: do not prepend whitespace to text between if..endif.

                  This feature is available in Postfix 3.2 and later.

           if !pattern

           endif  When a search string does not match the specified pattern, match
                  that search string against the patterns between  if  and  endif.
                  The  pattern  must  be in network/prefix or network_address form
                  (see ADDRESS PATTERN SYNTAX below). The if..endif can nest.

                  Note: do not prepend whitespace to text between if..endif.

                  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.

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

    ADDRESS PATTERN SYNTAX
           Postfix  CIDR  tables  are  pattern-based.  A  pattern is either a net-
           work_address which requires an exact match, or  a  network_address/pre-
           fix_length  where  the  prefix_length  part specifies the length of the
           network_address prefix that must be matched (the other bits in the net-
           work_address 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.

    INLINE SPECIFICATION
           The contents of a table may be specified in the table name (Postfix 3.7
           and later).  The basic syntax is:

           main.cf:
               parameter = .. cidr:{ { rule-1 }, { rule-2 } .. } ..

           master.cf:
               .. -o { parameter = .. cidr:{ { rule-1 }, { rule-2 } .. } .. } ..

           Postfix  recursively  expands any $parametername instances in the above
           parameter value, ignores whitespace  after  '{'  and  before  '}',  and
           writes each rule 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 $, specify $$ to keep Postfix from trying to
           do $name expansion as it evaluates a parameter value.

    EXAMPLE SMTPD ACCESS MAP
           /etc/postfix/main.cf:
               smtpd_client_restrictions = ... cidr:/etc/postfix/client.cidr ...

           /etc/postfix/client.cidr:
               # 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

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

    README FILES
           DATABASE_README, Postfix lookup table overview

    HISTORY
           CIDR table support was introduced with Postfix version 2.1.

    AUTHOR(S)
           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.
           111 8th Avenue
           New York, NY 10011, USA

                                                                     CIDR_TABLE(5)