RFC 3123 (rfc3123) - Page 2 of 8

A DNS RR Type for Lists of Address Prefixes (APL RR)

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RFC 3123                       DNS APL RR                      June 2001


3. APL RR Type

   An APL record has the DNS type of "APL" and a numeric value of 42
   [IANA].  The APL RR is defined in the IN class only.  APL RRs cause
   no additional section processing.

4. APL RDATA format

   The RDATA section consists of zero or more items () of the
   form

      +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
      |                          ADDRESSFAMILY                        |
      +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
      |             PREFIX            | N |         AFDLENGTH         |
      +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
      /                            AFDPART                            /
      |                                                               |
      +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+

      ADDRESSFAMILY     16 bit unsigned value as assigned by IANA
                        (see IANA Considerations)
      PREFIX            8 bit unsigned binary coded prefix length.
                        Upper and lower bounds and interpretation of
                        this value are address family specific.
      N                 negation flag, indicates the presence of the
                        "!" character in the textual format.  It has
                        the value "1" if the "!" was given, "0" else.
      AFDLENGTH         length in octets of the following address
                        family dependent part (7 bit unsigned).
      AFDPART           address family dependent part.  See below.

   This document defines the AFDPARTs for address families 1 (IPv4) and
   2 (IPv6).  Future revisions may deal with additional address
   families.

4.1. AFDPART for IPv4

   The encoding of an IPv4 address (address family 1) follows the
   encoding specified for the A RR by [RFC 1035], section 3.4.1.

   PREFIX specifies the number of bits of the IPv4 address starting at
   the most significant bit.  Legal values range from 0 to 32.

   Trailing zero octets do not bear any information (e.g., there is no
   semantic difference between 10.0.0.0/16 and 10/16) in an address
   prefix, so the shortest possible AFDLENGTH can be used to encode it.
   However, for DNSSEC [RFC 2535] a single wire encoding must be used by



Koch                          Experimental
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