INTERNAL IP mapping table

Modern MTA configurations typically make use of an   mapping table  as a convenient, single location for storing a site&#x27;s list of "internal" IP addresses. MTA components that need to check whether or not a source IP address is "internal" then can make use of the  mapping table for this determination, rather than each component having its own separate list. So while knowledge and use of the  mapping table is not hard-coded into the MTA, it is a common configuration feature.

Typical component users of an  mapping table include: the   mapping table (to determine SASL ruleset), and a backwards-pointing  IP literal rewrite rule  (for the purpose of    "switching" to the    channel).

A typical  mapping table might appear something like the following, shown from within  : msconfig&#x3e; show mapping:INTERNAL_IP.&#x2a; role.mapping:INTERNAL_IP.rule = host&#x27;s-public-IP-address $Y role.mapping:INTERNAL_IP.rule = $&#x3c;192.168.0.0/16&#x3e; $Y role.mapping:INTERNAL_IP.rule = ${::1} $Y role.mapping:INTERNAL_IP.rule = 127.0.0.1 $Y role.mapping:INTERNAL_IP.rule = &#x2a; $N or in legacy configuration: INTERNAL_IP host&#x27;s-public-IP-address   $Y $&#x3c;192.168.0.0/16&#x3e;          $Y ${::1}                     $Y 127.0.0.1                  $Y &#x2a;                          $N This sample  mapping table&#x27;s rules explicitly  match the host&#x27;s public IP address, use a  subnet match to match private IP addresses, and match IPv6 and IPv4 forms of loopback address. A final, fall-through wildcard  rule ensures that any IP addresses not listed/matched earlier in the   table will fail the mapping check (not be considered "internal").

See also:
 * Initial PORT_ACCESS mapping table
 * switchchannel Option
 * A rule to match any domain literal
 * Typical TCPIP channels and servers
 * Access mapping tables
 * Mapping entry patterns
 * Mapping entry patterns
 * Mapping tables