Internet Engineering Task Force                              G. Catalone
Internet Draft                                                R. Rockell
Document: draft-catalone-rockell-hadns-00.txt                     Sprint
Category: Informational                                        June 1999




            Implementation of a High Availability DNS System



Status of this Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026 [1].

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups. Note that
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   Drafts.

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   http://www.ietf.org/ietf/1id-abstracts.txt

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Abstract

   DNS servers have long suffered from availability and reachability
   issues. To that end, methods and techniques are developed to
   maintain the availability and reachability of this essential
   service.

   This Internet-Draft discusses one way that multiple DNS servers can
   share a common IP address and provide a high level of reachability
   and reliability.

   This technique may be useful in implementing other server
   configurations.

Conventions used in this Document

   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 RFC-2119 [1].


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Overview

   What we have done, at Sprint, is to assign the same IP address to
   several DNS servers on our network. This technique, we believe, will
   provide our customers with a highly available and reliable DNS
   service, without regard to the customer or server location on our
   network.

   All the DNS servers advertise the same address via BGP. The routing
   protocol itself decides which machine will be used at any given
   point in the network.

   In the event any particular DNS server becomes unavailable, that
   server's routing information is withdrawn from the network by the
   routing protocol and a new best route is chosen.

   Similarly, as a previously unavailable server becomes available, its
   routing information will be added to the network.


Server Setup

   The DNS server is configured in a normal fashion. If the machine
   hosting the DNS server does not provide native BGP service,
   additional software will need to be installed.

   The server will have its primary IP address and also a secondary.
   The secondary IP address would be the common address for all the
   servers in the DNS mesh.

   An AS number SHOULD be assigned to the DNS mesh: either an unused AS
   that the organization already has or a reserved AS [2]. It is
   possible to use one's current Autonomous System Number for this
   setup, but one must be wary of the following:

        The servers must be added correctly to your iBGP mesh.

        The routes must not violate backbone routing policies, and
        therefore must be tagged for non-transit to other providers if
        they are more specific than those that would normally traverse
        a peering. It is recommended that the common IP address come
        from an aggregatable block of address space that is sent to
        eBGP peers.

   One MAY also use a reserved Autonomous System ID here as well.
   However, care must be taken to ensure that the reserved AS is
   stripped to all eBGP peerings, and not leaked to the global Internet
   BGP table.

   The DNS server will announce its connected networks to its connected
   router via BGP. These connected networks will essentially be its
   primary LAN address and its secondary interface (common IP address).

Router Setup

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   The connected router is configured to see the DNS server as an
   external BPG peer. The router announces a default route to the DNS
   server.  Please note this configuration may be different dependant
   upon the choices made above (see section "Server Setup" for detail).

   The router tags these incoming routes with community strings in such
   a way to identify their origin when viewed in the routing table and
   to prevent them from being advertised to other external peers.

   Optionally, the router would need to be configured with appropriate
   access-lists to enforce local routing policies.


Security Considerations

   This Internet-Draft does not address any security considerations.


References

   [1]  Bradner, S., "The Internet Standards Process û Revision 3",
        BCP 9, RFC 2026, October 1996

   [2]  Bradner, S., "Key words for use in RFCs to Indicate Requirement
        Levels", BCP 14, RFC 2119, March 1997

   [3]  Hawkins & Bates, "Guidelines for Creation, Selection, and
        Registration of an Autonomous System (AS)", RFC 1930, March
        1996


Acknowledgments

   The authors would like to thank Michael Stevenson for his role in
   the design of this architecture and Abha Ahuja for her assistance in
   deployment.

Authors' Addresses

   Gregory S. Catalone Sr.
   12502 Sunrise Valley Drive
   VARESA0104
   Reston, VA 20196
   USA
   Phone: +1 703 689 7910
   Email: catalone@sprint.net

   Robert J. Rockell II
   12490 Sunrise Valley Drive
   VARESB0213
   Reston, VA 20196
   USA
   Phone: +1 703 689 6322
   Email: rrockell@sprint.net

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Copyright Statement

   Copyright (C) The Internet Society 1999. All Rights Reserved.




















































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