Network Working Group R. Elz
Request for Comments: 2182 University of Melbourne
BCP: 16 R. Bush
Category: Best Current Practice RGnet, Inc.
S. Bradner
Harvard University
M. Patton
Consultant
July 1997
Selection and Operation of Secondary DNS Servers
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.
Abstract
The Domain Name System requires that multiple servers exist for every
delegated domain (zone). This document discusses the selection of
secondary servers for DNS zones. Both the physical and topological
location of each server are material considerations when selecting
secondary servers. The number of servers appropriate for a zone is
also discussed, and some general secondary server maintenance issues
considered.
Elz, et al. Best Current Practice [Page 1]
RFC 2182 Selection and Operation of Secondary DNS Servers July 1997
Contents
Abstract ................................................... 1
1 Introduction ............................................... 2
2 Definitions ................................................ 2
3 Secondary Servers .......................................... 3
4 Unreachable servers ........................................ 5
5 How many secondaries? ...................................... 7
6 Finding Suitable Secondary Servers ......................... 8
7 Serial Number Maintenance .................................. 9
Security Considerations .................................... 11
References ................................................. 11
Acknowledgements ........................................... 11
Authors' Addresses ......................................... 11
1. Introduction
A number of problems in DNS operations today are attributable to poor
choices of secondary servers for DNS zones. The geographic placement
as well as the diversity of network connectivity exhibited by the set
of DNS servers for a zone can increase the reliability of that zone
as well as improve overall network performance and access
characteristics. Other considerations in server choice can
unexpectedly lower reliability or impose extra demands on the
network.
This document discusses many of the issues that should be considered
when selecting secondary servers for a zone. It offers guidance in
how to best choose servers to serve a given zone.
2. Definitions
For the purposes of this document, and only this document, the
following definitions apply:
DNS The Domain Name System [RFC1034, RFC1035].
Zone A part of the DNS tree, that is treated as a
unit.
Forward Zone A zone containing data mapping names to host
addresses, mail exchange targets, etc.
Elz, et al. Best Current Practice [Page 2]
RFC 2182 Selection and Operation of Secondary DNS Servers July 1997
Reverse Zone A zone containing data used to map addresses
to names.
Server An implementation of the DNS protocols able to
provide answers to queries. Answers may be
from information known by the server, or
information obtained from another server.
Authoritative Server A server that knows the content of a DNS zone
from local knowledge, and thus can answer
queries about that zone without needing to
query other servers.
Listed Server An Authoritative Server for which there is an
"NS" resource record (RR) in the zone.
Primary Server An authoritative server for which the zone
information is locally configured. Sometimes
known as a Master server.
Secondary Server An authoritative server that obtains
information about a zone from a Primary Server
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