Network Working Group                                     W. Kumari, Ed.
Internet-Draft                                                    Google
Intended status: Informational                           P. Hoffman, Ed.
Expires: April 28, 2015                                   VPN Consortium
                                                        October 25, 2014

   Decreasing Access Time to Root Servers by Running One on Loopback


   Some DNS recursive resolvers have longer-than-desired round trip
   times to the closest DNS root server.  Such resolvers can greatly
   decrease the rount trip time by running a copy of the full root zone
   on a loopback address (such as  This document shows how
   to start and maintain such a copy of the root zone in a manner that
   is secure for the operator of the recursive resolver and does not
   pose a threat to other users of the DNS.

Status of This Memo

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   This Internet-Draft will expire on April 28, 2015.

Copyright Notice

   Copyright (c) 2014 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
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   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements Notation . . . . . . . . . . . . . . . . . .   3
   2.  Requirements  . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Operation of the Root Zone on the Loopback Address  . . . . .   4
   4.  Using the Root Zone Server on the Loopback Address  . . . . .   4
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   4
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   5
   8.  Normative References  . . . . . . . . . . . . . . . . . . . .   5
   Appendix A.  Current Sources of the Root Zone . . . . . . . . . .   5
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   5

1.  Introduction

   DNS recursive resolvers have to answer all queries from their
   customers, even those which are for domain names that do not exist.
   For each queried name that has a top level domain (TLD) that is not
   in the recurive resolver's cache, the resolver must send a query to a
   root server to get the information for that TLD, or to find out that
   the TLD does not exist.  If there is a slow path between the
   recursive resolver and the closest root server, getting slow
   responses to these queries has a negative effect on the resolver's

   This document describes a method for the operator of a recursive
   resolver to greatly speed these queries.  The basic idea is to create
   a validated, up-to-date root zone server on a loopback address on the
   same host as the recursive server, and that server is added to the
   list of root zones that the recursive resolver uses for looking up
   root information.  If the new server is working correctly, it will
   quickly become the preferred root server for the recursive resolver;
   if the new server fails to work (such as because it cannot get
   updates to the zone), the recursive resolver will use other root
   servers, as it does now.

   The primary goal of this design is to provide faster negative
   responses to stub resolver queries that contain junk queries.  This
   design will probably have little effect on getting faster positive
   responses to stub resolver for good queries on TLDs, because the data
   for those zones is usually long-lived and already in the cache of the
   recursive resolver; thus, getting faster positive responses is a non-
   goal of this design.

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   This design explicitly only allows the new root zone server to be run
   on a loopback address.  This prevents the server from serving
   authoritative answers to any system other than the recurisve

   This design can possibly be implemented by hand, but it is much more
   likely that the creators of recursive resolver software will
   implement it and the operator simply needs to turn on the feature.
   Note that this design requires the addition of authoritative name
   server software running on the same machine as the recursive
   resolver.  Thus, recursive resolver software such as BIND will not
   need to add much new functionality, but recursive resolver software
   such as Unbound will need to add software that acts as an
   authoritative server.

1.1.  Requirements Notation

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in [RFC2119].

2.  Requirements

   In the discussion below, the term "legacy operation" means the way
   that a recursive resolver acts when it is not using the mechanism
   describe in this document, namely as a normal validating recursive
   resolver with no other special features.

   In order to implement the mechanism described in this document:

   o  The system MUST be able to validate a zone with DNSSEC.

   o  The system MUST have an up-to-date copy of the DNS root key.

   o  The system MUST be able to retrieve a copy of the entire root zone
      (including all DNSSEC-related records).

   o  The system MUST be able to run an authoritative server on one of
      the IPv4 loopback addresses (that is, an address in the range

   o  The authoritative server in the system MUST send error responses
      (RCODE 2, also known as "SERVFAIL") if the validated data in the
      root zone it is serving is out of date.

   o  The recursive resolver MUST be able to add an additional address
      to its list of addresses of authoritative root servers, and MUST
      treat that additional address the same as the other addresses.

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3.  Operation of the Root Zone on the Loopback Address

   The operation of an authoritative server for the root in the system
   described here can be done separately from the operation of the
   recursive resolver.

   The steps to set up the root zone are:

   1.  Retrieve a copy of the root zone.  (See Appendix A for some
       current locations of sources.)

   2.  Validate the zone using normal DNSSEC validation.

   3.  Start the authoritative server with the root zone on a loopback
       address that is not in use.  This would typically be,
       but if that address is in use, any address in 127/8 is

   The contents of the root zone must be refreshed using the timers from
   the SOA record in root zone, as described in [RFC1035].  If the
   contents of the zone cannot be refreshed with validated information
   before the expire time, the server MUST return a SERVFAIL error
   response for all queries until the zone can be successfully be set up

4.  Using the Root Zone Server on the Loopback Address

   A recursive resolver that wants to use a root zone server operating
   as described in Section 3 simply adds the address of the server to
   its list of authoritative servers for the root zone.  The resolver's
   round-robin search mechanism will begin to strongly prefer this new
   server, just as it would any root zone server that has an extremely
   short round trip time.

5.  IANA Considerations

   This document requires no action from the IANA.

6.  Security Considerations

   A system that does not follow the DNSSEC-related requirements given
   in Section 2 can be fooled into givning bad responses in the same way
   as any recursive resolver that does not do DNSSEC validation on
   responses from the root zone.

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7.  Acknowledgements

   The editors fully acknowledge that this is not a new concept, and
   that we have chatted with many people about this.  In fact, this
   concept may already have been implemented without the knowledge of
   the authors.

8.  Normative References

   [RFC1035]  Mockapetris, P., "Domain names - implementation and
              specification", STD 13, RFC 1035, November 1987.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

Appendix A.  Current Sources of the Root Zone

   The root zone can be retrieved from anywhere as long as it comes with
   all the DNSSEC records needed for validation.  Currently, there are
   three well-known sources of the root zone:

   o  From ICANN via FTP at

   o  From ICANN via HTTP at

   o  From ICANN by AXFR from DNS servers at and

Authors' Addresses

   Warren Kumari (editor)


   Paul Hoffman (editor)
   VPN Consortium


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