- 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.
- Copyright Notice
Copyright © The Internet Society (2000). All Rights Reserved.
As the internet becomes increasingly critical to the world's social
and economic infrastructure, attention has rightly focused on the
correct, safe, reliable, and secure operation of the internet
infrastructure itself. The root domain name servers are seen as a
crucial part of that technical infrastructure. The primary focus of
this document is to provide guidelines for operation of the root name
servers. Other major zone server operators (gTLDs, ccTLDs, major
zones) may also find it useful. These guidelines are intended to
meet the perceived societal needs without overly prescribing
- 1 Background
The resolution of domain names on the internet is critically
dependent on the proper, safe, and secure operation of the root
domain name servers. Currently, these dozen or so servers are
provided and operated by a very competent and trusted group of
volunteers. This document does not propose to change that, but
merely to provide formal guidelines so that the community understands
how and why this is done.
- 1.1 The Internet Corporation for Assigned Names and Numbers (ICANN)
has become responsible for the operation of the root servers.
The ICANN has appointed a Root Server System Advisory Committee
(RSSAC) to give technical and operational advice to the ICANN
board. The ICANN and the RSSAC look to the IETF to provide
- 1.2 The root servers serve the root, aka ".", zone. Although today
some of the root servers also serve some TLDs (top level domains)
such as gTLDs (COM, NET, ORG, etc.), infrastructural TLDs such as
INT and IN-ADDR.ARPA, and some ccTLDs (country code TLDs, e.g. SE
for Sweden), this is likely to change (see 2.5).
- 1.3 The root servers are neither involved with nor dependent upon the
- 1.4 The domain name system has proven to be sufficiently robust that
we are confident that the, presumably temporary, loss of most of
the root servers should not significantly affect operation of the
- 1.5 Experience has shown that the internet is quite vulnerable to
incorrect data in the root zone or TLDs. Hence authentication,
validation, and security of these data are of great concern.
- 2 The Servers Themselves
The following are requirements for the technical details of the root
- 2.1 It would be short-sighted of this document to specify particular
hardware, operating systems, or name serving software.
Variations in these areas would actually add overall robustness.
- 2.2 Each server MUST run software which correctly implements the IETF
standards for the DNS, currently [RFC1035] [RFC2181]. While
there are no formal test suites for standards compliance, the
maintainers of software used on root servers are expected to take
all reasonable actions to conform to the IETF's then current
- 2.3 At any time, each server MUST be able to handle a load of
requests for root data which is three times the measured peak of
such requests on the most loaded server in then current normal
conditions. This is usually expressed in requests per second.
This is intended to ensure continued operation of root services
should two thirds of the servers be taken out of operation,
whether by intent, accident, or malice.
- 2.4 Each root server should have sufficient connectivity to the
internet to support the bandwidth needs of the above requirement.
Connectivity to the internet SHOULD be as diverse as possible.
Root servers SHOULD have mechanisms in place to accept IP
connectivity to the root server from any internet provider
delivering connectivity at their own cost.
- 2.5 Servers MUST provide authoritative responses only from the zones
they serve. The servers MUST disable recursive lookup,
forwarding, or any other function that may allow them to provide
cached answers. They also MUST NOT provide secondary service for
any zones other than the root and root-servers.net zones. These
restrictions help prevent undue load on the root servers and
reduce the chance of their caching incorrect data.
- 2.6 Root servers MUST answer queries from any internet host, i.e. may
not block root name resolution from any valid IP address, except
in the case of queries causing operational problems, in which
case the blocking SHOULD last only as long as the problem, and be
as specific as reasonably possible.
- 2.7 Root servers SHOULD NOT answer AXFR, or other zone transfer,
queries from clients other than other root servers. This
restriction is intended to, among other things, prevent
unnecessary load on the root servers as advice has been heard
such as "To avoid having a corruptible cache, make your server a
stealth secondary for the root zone." The root servers MAY put
the root zone up for ftp or other access on one or more less
- 2.8 Servers MUST generate checksums when sending UDP datagrams and
MUST verify checksums when receiving UDP datagrams containing a
- 3 Security Considerations
The servers need both physical and protocol security as well as
unambiguous authentication of their responses.
- 3.1 Physical security MUST be ensured in a manner expected of data
centers critical to a major enterprise.
- 3.1.1 Whether or not the overall site in which a root server is
located has access control, the specific area in which the
root server is located MUST have positive access control,
i.e. the number of individuals permitted access to the
area MUST be limited, controlled, and recorded. At a
minimum, control measures SHOULD be either mechanical or
electronic locks. Physical security MAY be enhanced by
the use of intrusion detection and motion sensors,
multiple serial access points, security personnel, etc.
- 3.1.2 Unless there is documentable experience that the local
power grid is more reliable than the MTBF of a UPS (i.e.
five to ten years), power continuity for at least 48 hours
MUST be assured, whether through on-site batteries, on-
site power generation, or some combination thereof. This
MUST supply the server itself, as well as the
infrastructure necessary to connect the server to the
internet. There MUST be procedures which ensure that
power fallback mechanisms and supplies are tested no less
frequently than the specifications and recommendations of
- 3.1.3 Fire detection and/or retardation MUST be provided.
- 3.1.4 Provision MUST be made for rapid return to operation after
a system outage. This SHOULD involve backup of systems
software and configuration. But SHOULD also involve
backup hardware which is pre-configured and ready to take
over operation, which MAY require manual procedures.
- 3.2 Network security should be of the level provided for critical
infrastructure of a major commercial enterprise.
- 3.2.1 The root servers themselves MUST NOT provide services
other than root name service e.g. remote internet
protocols such as http, telnet, rlogin, ftp, etc. The
only login accounts permitted should be for the server
administrator(s). "Root" or "privileged user" access MUST
NOT be permitted except through an intermediate user
Servers MUST have a secure mechanism for remote
administrative access and maintenance. Failures happen;
given the 24x7 support requirement (per 4.5), there will
be times when something breaks badly enough that senior
wizards will have to connect remotely. Remote logins MUST
be protected by a secure means that is strongly
authenticated and encrypted, and sites from which remote
login is allowed MUST be protected and hardened.
- 3.2.2 Root name servers SHOULD NOT trust other hosts, except
secondary servers trusting the primary server, for matters
of authentication, encryption keys, or other access or
security information. If a root operator uses kerberos
authentication to manage access to the root server, then
the associated kerberos key server MUST be protected with
the same prudence as the root server itself. This applies
to all related services which are trusted in any manner.
- 3.2.3 The LAN segment(s) on which a root server is homed MUST
NOT also home crackable hosts. I.e. the LAN segments
should be switched or routed so there is no possibility of
masquerading. Some LAN switches aren't suitable for
security purposes, there have been published attacks on
their filtering. While these can often be prevented by
careful configuration, extreme prudence is recommended.
It is best if the LAN segment simply does not have any
other hosts on it.
- 3.2.4 The LAN segment(s) on which a root server is homed SHOULD
be separately firewalled or packet filtered to discourage
network access to any port other than those needed for
- 3.2.5 The root servers SHOULD have their clocks synchronized via
NTP [RFC1305] [RFC2030] or similar mechanisms, in as
secure manner as possible. For this purpose, servers and
their associated firewalls SHOULD allow the root servers
to be NTP clients. Root servers MUST NOT act as NTP peers
- 3.2.6 All attempts at intrusion or other compromise SHOULD be
logged, and all such logs from all root servers SHOULD be
analyzed by a cooperative security team communicating with
all server operators to look for patterns, serious
attempts, etc. Servers SHOULD log in GMT to facilitate
- 3.2.7 Server logging SHOULD be to separate hosts which SHOULD be
protected similarly to the root servers themselves.
- 3.2.8 The server SHOULD be protected from attacks based on
source routing. The server MUST NOT rely on address- or
- 3.2.9 The network on which the server is homed SHOULD have
- 3.3 Protocol authentication and security are required to ensure that
data presented by the root servers are those created by those
authorized to maintain the root zone data.
- 3.3.1 The root zone MUST be signed by the Internet Assigned
Numbers Authority (IANA) in accordance with DNSSEC, see
[RFC2535] or its replacements. It is understood that
DNSSEC is not yet deployable on some common platforms, but
will be deployed when supported.
- 3.3.2 Root servers MUST be DNSSEC-capable so that queries may be
authenticated by clients with security and authentication
concerns. It is understood that DNSSEC is not yet
deployable on some common platforms, but will be deployed
- 3.3.3 Transfer of the root zone between root servers MUST be
authenticated and be as secure as reasonably possible.
Out of band security validation of updates MUST be
supported. Servers MUST use DNSSEC to authenticate root
zones received from other servers. It is understood that
DNSSEC is not yet deployable on some common platforms, but
will be deployed when supported.
- 3.3.4 A 'hidden primary' server, which only allows access by the
authorized secondary root servers, MAY be used.
- 3.3.5 Root zone updates SHOULD only progress after a number of
heuristic checks designed to detect erroneous updates have
been passed. In case the update fails the tests, human
intervention MUST be requested.
- 3.3.6 Root zone updates SHOULD normally be effective no later
than 6 hours from notification of the root server
- 3.3.7 A special procedure for emergency updates SHOULD be
defined. Updates initiated by the emergency procedure
SHOULD be made no later than 12 hours after notification.
- 3.3.8 In the advent of a critical network failure, each root
server MUST have a method to update the root zone data via
a medium which is delivered through an alternative, non-
- 3.3.9 Each root MUST keep global statistics on the amount and
types of queries received/answered on a daily basis. These
statistics must be made available to RSSAC and RSSAC
sponsored researchers to help determine how to better
deploy these machines more efficiently across the
internet. Each root MAY collect data snapshots to help
determine data points such as DNS query storms,
significant implementation bugs, etc.
- 4 Communications
Communications and coordination between root server operators and
between the operators and the IANA and ICANN are necessary.
- 4.1 Planned outages and other down times SHOULD be coordinated
between root server operators to ensure that a significant number
of the root servers are not all down at the same time.
Preannouncement of planned outages also keeps other operators
from wasting time wondering about any anomalies.
- 4.2 Root server operators SHOULD coordinate backup timing so that
many servers are not off-line being backed up at the same time.
Backups SHOULD be frequently transferred off site.
- 4.3 Root server operators SHOULD exchange log files, particularly as
they relate to security, loading, and other significant events.
This MAY be through a central log coordination point, or MAY be
- 4.4 Statistics as they concern usage rates, loading, and resource
utilization SHOULD be exchanged between operators, and MUST be
reported to the IANA for planning and reporting purposes.
- 4.5 Root name server administrative personnel MUST be available to
provide service 24 hours a day, 7 days per week. On call
personnel MAY be used to provide this service outside of normal
- 5 Acknowledgements
The authors would like to thank Scott Bradner, Robert Elz, Chris
Fletcher, John Klensin, Steve Bellovin, and Vern Paxson for their
- 6 References
[RFC1035] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, November 1987.
[RFC1305] Mills, D., "Network Time Protocol (Version 3)
Specification, Implementation", RFC 1305, March 1992.
[RFC2030] Mills, D., "Simple Network Time Protocol (SNTP) Version 4
for IPv4, IPv6 and OSI", RFC 2030, October 1996.
[RFC2181] Elz, R. and R. Bush, "Clarifications to the DNS
Specification", RFC 2181, July 1997.
[RFC2535] Eastlake, D. and C. Kaufman, "Domain Name System Security
Extensions", RFC 2535, March 1999.
- 7 Authors' Addresses
5147 Crystal Springs
Bainbridge Island, WA US-98110
Phone: +1 206 780 0431
RIPE Network Coordination Centre (NCC)
NL-1016 AB Amsterdam
Phone: +31 20 535 4444
505 Huntmar Park Drive
Herndon, VA 22070-5100
Phone: +1 703 742 0400
1710 Goodridge Drive
McLean, Virginia 22102
+1 703 821 6535
- 8 Specification of Requirements
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.
- 9 Full Copyright Statement
Copyright © The Internet Society (2000). All Rights Reserved.
This document and translations of it may be copied and furnished to
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included on all such copies and derivative works. However, this
document itself may not be modified in any way, such as by removing
the copyright notice or references to the Internet Society or other
Internet organizations, except as needed for the purpose of
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The limited permissions granted above are perpetual and will not be
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