Classless IN-ADDR.ARPA delegation
RFC 2317
Document | Type |
RFC - Best Current Practice
(March 1998; Errata)
Also known as BCP 20
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Authors | Havard Eidnes , Paul Vixie , Geert de Groot | ||
Last updated | 2013-03-02 | ||
Stream | Internent Engineering Task Force (IETF) | ||
Formats | plain text html pdf htmlized (tools) htmlized bibtex | ||
Stream | WG state | (None) | |
Document shepherd | No shepherd assigned | ||
IESG | IESG state | RFC 2317 (Best Current Practice) | |
Consensus Boilerplate | Unknown | ||
Telechat date | |||
Responsible AD | (None) | ||
Send notices to | (None) |
Network Working Group H. Eidnes Request for Comments: 2317 SINTEF RUNIT BCP: 20 G. de Groot Category: Best Current Practice Berkeley Software Design, Inc. P. Vixie Internet Software Consortium March 1998 Classless IN-ADDR.ARPA delegation Status of this Memo This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. Distribution of this memo is unlimited. Copyright Notice Copyright (C) The Internet Society (1998). All Rights Reserved. 2. Introduction This document describes a way to do IN-ADDR.ARPA delegation on non- octet boundaries for address spaces covering fewer than 256 addresses. The proposed method should thus remove one of the objections to subnet on non-octet boundaries but perhaps more significantly, make it possible to assign IP address space in smaller chunks than 24-bit prefixes, without losing the ability to delegate authority for the corresponding IN-ADDR.ARPA mappings. The proposed method is fully compatible with the original DNS lookup mechanisms specified in [1], i.e. there is no need to modify the lookup algorithm used, and there should be no need to modify any software which does DNS lookups. The document also discusses some operational considerations to provide some guidance in implementing this method. 3. Motivation With the proliferation of classless routing technology, it has become feasible to assign address space on non-octet boundaries. In case of a very small organization with only a few hosts, assigning a full 24-bit prefix (what was traditionally referred to as a "class C network number") often leads to inefficient address space utilization. Eidnes, et. al. Best Current Practice [Page 1] RFC 2317 Classless IN-ADDR.ARPA delegation March 1998 One of the problems encountered when assigning a longer prefix (less address space) is that it seems impossible for such an organization to maintain its own reverse ("IN-ADDR.ARPA") zone autonomously. By use of the reverse delegation method described below, the most important objection to assignment of longer prefixes to unrelated organizations can be removed. Let us assume we have assigned the address spaces to three different parties as follows: 192.0.2.0/25 to organization A 192.0.2.128/26 to organization B 192.0.2.192/26 to organization C In the classical approach, this would lead to a single zone like this: $ORIGIN 2.0.192.in-addr.arpa. ; 1 PTR host1.A.domain. 2 PTR host2.A.domain. 3 PTR host3.A.domain. ; 129 PTR host1.B.domain. 130 PTR host2.B.domain. 131 PTR host3.B.domain. ; 193 PTR host1.C.domain. 194 PTR host2.C.domain. 195 PTR host3.C.domain. The administration of this zone is problematic. Authority for this zone can only be delegated once, and this usually translates into "this zone can only be administered by one organization." The other organizations with address space that corresponds to entries in this zone would thus have to depend on another organization for their address to name translation. With the proposed method, this potential problem can be avoided. 4. Classless IN-ADDR.ARPA delegation Since a single zone can only be delegated once, we need more points to do delegation on to solve the problem above. These extra points of delegation can be introduced by extending the IN-ADDR.ARPA tree downwards, e.g. by using the first address or the first address and the network mask length (as shown below) in the corresponding address Eidnes, et. al. Best Current Practice [Page 2] RFC 2317 Classless IN-ADDR.ARPA delegation March 1998 space to form the the first component in the name for the zones. The following four zone files show how the problem in the motivation section could be solved using this method. $ORIGIN 2.0.192.in-addr.arpa. @ IN SOA my-ns.my.domain. hostmaster.my.domain. (...) ;... ; <<0-127>> /25 0/25 NS ns.A.domain. 0/25 NS some.other.name.server. ; 1 CNAME 1.0/25.2.0.192.in-addr.arpa. 2 CNAME 2.0/25.2.0.192.in-addr.arpa. 3 CNAME 3.0/25.2.0.192.in-addr.arpa. ; ; <<128-191>> /26 128/26 NS ns.B.domain.Show full document text