A Suggested Scheme for DNS Resolution of Networks and Gateways
RFC 4183
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RFC - Informational
(September 2005; No errata)
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Author |
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Edward Warnicke
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Last updated |
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2015-10-14
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ISE
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plain text
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(None)
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Consensus Boilerplate |
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No shepherd assigned
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IESG |
IESG state |
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RFC 4183 (Informational)
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Telechat date |
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Responsible AD |
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David Kessens
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Network Working Group E. Warnicke
Request for Comments: 4183 Cisco Systems
Category: Informational September 2005
A Suggested Scheme for DNS Resolution of Networks and Gateways
Status of This Memo
This memo provides information for the Internet community. It does
not specify an Internet standard of any kind. Distribution of this
memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (2005).
IESG Note
This RFC is not a candidate for any level of Internet Standard. The
IETF disclaims any knowledge of the fitness of this RFC for any
purpose and notes that the decision to publish is not based on IETF
review apart from IESG review for conflict with IETF work. The RFC
Editor has chosen to publish this document at its discretion. See
RFC 3932 [6] for more information.
Abstract
This document suggests a method of using DNS to determine the network
that contains a specified IP address, the netmask of that network,
and the address(es) of first-hop routers(s) on that network. This
method supports variable-length subnet masks, delegation of subnets
on non-octet boundaries, and multiple routers per subnet.
1. Introduction
As a variety of new devices are introduced to the network, many of
them not traditional workstations or routers, there are requirements
that the first-hop router provide some network service for a host.
It may be necessary for a third-party server in the network to
request some service related to the host from the first-hop router(s)
for that host. It would be useful to have a standard mechanism for
such a third-party device to find the first-hop router(s) for that
host.
DNS-based mechanisms have been defined for the resolution of router
addresses for classful networks (RFC 1035 [1]) and of subnets (RFC
1101 [2]). RFC 1101 suffers from a number of defects, chief among
Warnicke Informational [Page 1]
RFC 4183 DNSNET September 2005
which are that it does not support variable-length subnet masks,
which are commonly deployed in the Internet. The present document
defines DNS-based mechanisms to cure these defects.
Since the writing of RFC 1101, DNS mechanisms for dealing with
classless networks have been defined, for example, RFC 2317 [3].
This document describes a mechanism that uses notation similar to
that of RFC 2317 to specify a series of PTR records enumerating the
subnets of a given network in the RFC 2317 notation. This lookup
process continues until the contents of the PTR records are not an
in-addr.arpa.-derived domain name. These terminal PTR record values
are treated as the hostname(s) of the router(s) on that network.
This RFC also specifies an extension to the method of RFC 2317 to
support delegation at non-octet boundaries.
2. Generic Format of a Network Domain Name
Using the Augmented BNF of RFC 2234 [4], we can describe a generic
domain name for a network as follows:
networkdomainname = maskedoctet "." *( decimaloctet / maskedoctet
".") "in-addr.arpa."
maskedoctet = decimaloctet "-" mask
mask = 1*2DIGIT ; representing a decimal integer value in the
; range 1-32
decimaloctet = 1*3DIGIT ; representing a decimal integer value in
; the range 0 through 255
By way of reference, an IPv4 CIDR notation network address would
be written
IPv4CIDR = decimaloctet "." decimaloctet "." decimaloctet "."
decimaloctet "/" mask
A "-" is used as a delimiter in a maskedoctet instead of a "/" as in
RFC 2317 out of concern about compatibility with existing DNS
servers, many of which do not consider "/" to be a valid character in
a hostname.
3. Non-Octet Boundary Delegation
In RFC 2317, there is no mechanism for non-octet boundary delegation.
Networks would be represented as being part of the domain of the next
octet.
Warnicke Informational [Page 2]
RFC 4183 DNSNET September 2005
Examples:
10.100.2.0/26 -> 0-26.2.100.10.in-addr.arpa.
10.20.128.0/23 -> 128-23.20.10.in-addr.arpa.
10.192.0.0/13 -> 192-13.10.in-addr.arpa.
In the event that the entity subnetting does not actually own the
network being subnetted on an octet break, a mechanism needs to be
available to allow for the specification of those subnets. The
mechanism is to allow the use of maskedoctet labels as delegation
shims.
For example, consider an entity A that controls a network
10.1.0.0/16. Entity A delegates to entity B the network 10.1.0.0/18.
In order to avoid having to update entries for entity B whenever
entity B updates subnetting, entity A delegates the
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