Non-Terminal DNS Name Redirection (RFC2672)
Original Publication Date: 1999-Aug-01
Included in the Prior Art Database: 2019-Feb-11
Internet Society Requests For Comment (RFCs)
This document defines a new DNS Resource Record called "DNAME", which provides the capability to map an entire subtree of the DNS name space to another domain. [STANDARDS-TRACK]
Network Working Group M. Crawford Request for Comments: 2672 Fermilab Category: Standards Track August 1999
Non-Terminal DNS Name Redirection
Status of this Memo
This document specifies an Internet standards track protocol for the Internet community, and requests discussion and suggestions for improvements. Please refer to the current edition of the "Internet Official Protocol Standards" (STD 1) for the standardization state and status of this protocol. Distribution of this memo is unlimited.
Copyright (C) The Internet Society (1999). All Rights Reserved.
This document defines a new DNS Resource Record called "DNAME", which provides the capability to map an entire subtree of the DNS name space to another domain. It differs from the CNAME record which maps a single node of the name space.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [KWORD].
This Resource Record and its processing rules were conceived as a solution to the problem of maintaining address-to-name mappings in a context of network renumbering. Without the DNAME mechanism, an authoritative DNS server for the address-to-name mappings of some network must be reconfigured when that network is renumbered. With DNAME, the zone can be constructed so that it needs no modification when renumbered. DNAME can also be useful in other situations, such as when an organizational unit is renamed.
3. The DNAME Resource Record
The DNAME RR has mnemonic DNAME and type code 39 (decimal).
Crawford Standards Track [Page 1]
RFC 2672 Non-Terminal DNS Name Redirection August 1999
DNAME has the following format:
<owner> <ttl> <class> DNAME <target>
The format is not class-sensitive. All fields are required. The RDATA field <target> is a <domain-name> [DNSIS].
The DNAME RR causes type NS additional section processing.
The effect of the DNAME record is the substitution of the record’s <target> for its <owner> as a suffix of a domain name. A "no- descendants" limitation governs the use of DNAMEs in a zone file:
If a DNAME RR is present at a node N, there may be other data at N (except a CNAME or another DNAME), but there MUST be no data at any descendant of N. This restriction applies only to records of the same class as the DNAME record.
This rule assures predictable results when a DNAME record is cached by a server which is not authoritative for the record’s zone. It MUST be enforced when authoritative zone data is loaded. Together with the rules for DNS zone authority [DNSCLR] it implies that DNAME and NS records can only coexist at the top of a zone which has only one node.
The compression scheme of [DNSIS] MUST NOT be applied to the RDATA portion of a DNAME record unless the sending server has some way of knowing that the receiver understands the DNAME record format. Signalling such understanding is expected to be the subj...