Background

The 'APL' Resource Record (RR) is standarized in RFC 3123 and defines an Address Prefix List that may be used to define one or more IP addresses or IP address ranges for any required purpose.


Details

RR Type: APL
ID: 42 (0x002A)
Defining RFC: RFC 3123
Description: Address Prefix List
Function: Specify lists of address ranges, e.g. in CIDR format, for various address families.
Status: Active

'APL' RR Syntax

name ttl class type rdata {addressfamily, prefix, n, afdlength, afdpart}

RR Field Example Description
name foo The name is unqualified, causing $ORIGIN substitution. You can also write this as a fully qualified domain name (FQDN) such as foo.yourdomain.com.

Blank Name - A record that has nothing in the 'name' field gets used for all requests being made to the base domain such as yourdomain.com. (Same as Parent)
ttl This is the records time to live value (in seconds). If there is no TTL specified, the zone's default $TTL Directive will be used.
type APL Specifies the RDATA field will contain data in the APL RDATA format.
class IN Specifies the class to be 'Internet'.
rdata addressfamily 1 16 bit unsigned value as assigned by IANA
rdata prefix /21 8 bit unsigned binary coded prefix length. Upper and lower bounds and interpretation of this value are address family specific.
rdata n Negation flag, indicates the presence of the "!" character in the textual format. It has the value "1" if the "!" was given, "0" else.
rdata afdlength Length in octets of the following address family dependent part (7 bit unsigned).
rdata afdpart 127.0.0.1 Address family dependent part.

Examples

Snippets from a fictitious forward lookup 'yourdomain.com' zone file

Typical 'APL' Record Entries

;   RFC 1101-like announcement of address ranges for foo.example
foo IN APL 1:192.168.32.0/21   !1:192.168.38.0/28
 
;   CIDR blocks covered by classless delegation
42.168.192.IN-ADDR.ARPA. IN APL ( 1:192.168.42.0/26   1:192.168.42.64/26   1:192.168.42.128/25 )
 
;   Zone transfer restriction
_axfr.sbo.yourdomain.com. IN APL 1:127.0.0.1/32   1:172.16.64.0/22
 
;   List of address ranges for multicast
multicast.yourdomain.com. IN APL 1:224.0.0.0/4   2:FF00:0:0:0:0:0:0:0/8


See Also




This content was last updated on December 21, 2020
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