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Network Working Group B. Manning Request for Comments: 2010 ISI Category: Informational P. Vixie

                                                          October 1996
             Operational Criteria for Root Name Servers

Status of this Memo

 This memo provides information for the Internet community.  This memo
 does not specify an Internet standard of any kind.  Distribution of
 this memo is unlimited.


 This document specifies the operational requirements of root name
 servers, including host hardware capacities, name server software
 revisions, network connectivity, and physical environment.

1 - Rationale and Scope

 1.1. Historically, the name servers responsible for the root (".")
 zone have also been responsible for all international top-level
 domains (iTLD's, for example: COM, EDU, INT, ARPA).  These name
 servers have been operated by a cadre of highly capable volunteers,
 and their administration has been loosely coordinated by the NIC
 (first SRI-NIC and now InterNIC).  Ultimate responsibility for the
 correct operation of these servers and for the content of the DNS
 zones they served has always rested with the IANA.
 1.2. As described in [Postel96], many new TLD's may be created
 shortly.  Servers for all new and existing iTLD's will be subject to
 the operational requirements given in [Postel96].  The set of servers
 for the root (".")  zone is likely to become disjoint from the set of
 servers for any TLD or group of TLD's, including those maintained by
 the InterNIC.

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 1.3. In spite of the similarities in operational requirements between
 the servers for the iTLD's and the servers for the root (".") zone,
 they are in fact different server sets with different administrators
 and slightly different operational requirements. It is likely that
 many contry code tld servers will have even more divergent
 operational requirements. That said, the requirements set down in
 this document could be successfully applied to any name server
 (whether root, top level, or any other level), but may be more
 draconian than necessary for servers other than those of the root
 (".") zone.
 Disclaimer:  The selection of name server locations and
              administrators, and the procedures for addressing
              noncompliance with these stated operational
              requirements, are outside the scope of this document.
 Definition:  For the purpose of this document, the term "zone master"
              shall be used to designate the administrative owner of
              the content of a zone.  This person is expected to have
              final responsibility for the selection and correct
              operation of all of the zone's servers.  For the root
              (".") zone, this is the IANA.

2 - Operational Requirements

 2.1. Name server software.  The zone master shall initially and
 periodically choose a name server package to run on all of the zone's
 servers.  It is expected that the BIND server will be used, at least
 initially, and that new versions or other servers will be specified
 from time to time.
   Rationale:  This requirement is based on the wide and free
               availability of BIND's source code, and the active
               analysis and development it constantly receives from
               several members of the IETF.
 Name server software upgrades will be specified and scheduled by the
 zone master, and must occur on all of a zone's servers within a
 specified 96 hour window.
   Rationale:  In some cases it has proven necessary to "cold start" a
               zone's servers in order to clear out oscillating bad
               data.  By forcing all software upgrades to happen at
               about the same time, it will be possible to coordinate
               a software change with a zone content change.

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 2.2. UDP checksums.  UDP checksums must be generated when sending
 datagrams, and verified when receiving them.
   Rationale:  Some vendors turn off UDP checksums for performance
               reasons, citing the presence of MAC-level frame checks
               (CRC, for example) as "strong enough."  This has been
               a disaster in actual practice.
 2.3. Dedicated host.  A name server host should have no other
 function, and no login accounts other than for system or network
 administrators.  No other network protocols should be served by a
 name server host (e.g., SMTP, NNTP, FTP, et al).  If login is
 permitted from other than the system console, then the login service
 must be by encrypted channel (e.g., Kerberized and encrypted
 rlogin/telnet, the secure shell (SSH), or an equivilent).
   Rationale:  Each additional service performed by a host makes it
               less reliable and potentially less secure, as well as
               complicating fault isolation procedures.  While name
               service does not consume very much in the way of system
               resources, it is thought best that a host do a few
               things well rather than many things poorly.
 2.4. Clock synchronization.  A name server host should synchronize
 its clock using the NTP protocol (currnet version) with
 authentication.  At least two NTP servers should be used.  As an
 exception to section 2.3 above, a name server host can be an NTP
 server as well.
   Rationale:  For distributed fault isolation reasons, synchronized
               time stamps in system event logs are quite helpful.
               NTP is easily spoofed by UDP blast attacks, thus the
               requirement for authentication between the name server
               host and its NTP servers.  A name server host is
               allowed to be an NTP server because it has been
               observed that a single host running both name service
               and stratum 1 NTP is still quite reliable and secure.
 2.5. Network interfaces.  Name servers must send UDP responses with
 an IP source address (and UDP source port number) equal to the IP
 destination address (and UDP destination port number) of the request.
 Also, a name server might have multiple real interfaces, but only one
 will be advertised in the zone's NS RRset and associated glue A RRs.
 The advertised address should be that of the "best" interface on the
 host, in terms of network performance and reliability to the largest
 number of destinations.

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   Rationale:  While not required by [RFC1035], many extant DNS
               implementations require the source address and port of
               a reply to match the destination address and port to
               which the request was sent.  The number of advertised
               addresses is limited to one (1) so that DNS delegation
               responses containing this name server can be as short
               as possible.
 2.6. Physical environment.  A name server host must be located in a
 secure space such as a locked computer room or a data center with
 restricted access.  The power supply should be redundant, using
 batteries, generators or some other means to protect against utility
 power failures.  Network connectivity should be redundant, so that a
 single wide area line failure cannot completely isolate the name
 server host from the rest of the network.
 2.7. Network security.  The system and network administrators should
 educate themselves about potential threats, and stay current on CERT
 bulletins regarding network breakins.  The system staff should
 periodically audit the name server host's activity logs and be able
 to detect breakins during or after the fact.
 2.8. Host performance.  As of the time of this writing, a name server
 must be able to answer 1,200 UDP transactions per second with less
 than 5 milliseconds of average latency.  Because the network is still
 growing at a high rate, the ability to grow to 2,000 transactions per
 second and still support a 5 millisecond latency is highly desirable.
 Note that this requirement affects both the host and the network
 infrastructure to which that host is attached.
 2.9. Response time.  The administrators responsible for a name server
 will respond to e-mail trouble reports within 24 hours.  Personnel
 issues such as vacations and illness will cause responsibilities to
 be delegated and/or reassigned rather than ignored.  After hours
 telephone numbers must be made available to the zone master for
 nonpublished use in emergencies.  An escalation contact name, e-mail
 address, and telephone number will also be made available to the zone
 master in the event of nonresponse through the normal channel.
 2.10. Zone transfer access control.  The name server shall be
 configured so that outbound zone transfers are permitted only to
 destinations on the server's local networks, and to whichever
 networks the zone master designates for remote debugging purposes.

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   Rationale:  Zone transfers can present a significant load on a name
               server, especially if several transfers are started
               simultaneously against the same server.  There is no
               operational reason to allow anyone outside the name
               server's and zone's administrators to transfer the
               entire zone.
 2.11. Zone transfer protocol.  DNS AXFR shall be used in preference
 to FTP or any other non-DNS transfer protocol.  DNS NOTIFY (see
 [NOTIFY]) and DNS IXFR (see [IXFR]) shall be supported and enabled
 when available.
   Rationale:  Historically, the common implementations of DNS
               (a.k.a., BIND) did not support zone transfer of the
               root (".") zone due to programming errors.  Thus, FTP
               was used.  In the future, DNS implementations which do
               not support zone transfer of all zones will not be
               considered suitable for use as root name servers.  The
               benefits of [IXFR] and [NOTIFY] should be obvious.
 2.12. Recursion shall be disabled for queries.
   Rationale:  Recursion is a major source of cache pollution, and can
               be a major drain on name server performance.  An
               organization's recursive DNS needs should be served by
               some other host than its root name server(s).  An
               exception is made for missing glue since it's possible
               that glue needed for some delegations will not be
               within or beneath any zone for which the server is
               authoritative.  Such glue must be fetched via
               recursive lookups to other servers.
 2.13. Outages shall be reported.  All outages, scheduled or not,
 shall be reported to the zone master via e-mail.  If an outage is
 unscheduled or if an outage is scheduled less than 24 hours in
 advance, then an additional notification of the zone master shall be
 made via telephone.  Extended or repeated outages may beget special
 handling by the zone master.
 2.14. Inverse name lookups.  The PTR RR associated with a server's
 primary interface address (that is, the address shown in in the
 zone's delegation) shall have its target specified by the zone

Manning & Vixie Informational [Page 5] RFC 2010 DNSSVR Criteria October 1996

   Rationale:  Since each organization has local control of their
               network's PTR RRs, and since it is necessary for the
               correct operation of some software that the forward and
               reverse lookups have symmetrical results, it is left
               up to the zone master to select the name for each
               authority server's primary address.

3 - Possible Selection Criteria

 3.1. Host population.  A server's location on the network should be
 such that it has a low IP hop count to a high number of end hosts.
 Duplication of service should be avoided, such that any given set of
 end hosts needs to have a low IP hop count to at most one authority
 server for any given zone.
 3.2. Infrastructure diversity.  A server's location on the network
 should be such that most failures capable of isolating it from a
 large number of end hosts are diverse from the failures capable of
 similarly isolating other authority servers for the same zone(s).

4 - Security Considerations

 See section 2.7.

5 - References

    Mockapetris, P., "Domain Names - Implementation and Specification",
    STD 13, RFC 1035, USC/Information Sciences Institute, November
    Postel, J., "New Registries and the Delegation of International Top
    Level Domains", Work in Progress.
    Ohta, M., "Incremental Zone Transfer", RFC 1995, August 1996.
    Vixie, P., "A Mechanism for Prompt Notification of Zone Changes",
    RFC 1996, August 1996.

6 - Acknowledgements

 Constructive comments have been received from:  Jon Postel, Michael
 Patton, Andrew Partan, Michael Dillon, Don Mitchell Steven Doyle,
 Owen DeLong and other members of the internet community.

Manning & Vixie Informational [Page 6] RFC 2010 DNSSVR Criteria October 1996

7 - Authors' Addresses

   Bill Manning
   4676 Admiralty Way
   Marina del Rey, CA 90292
   Phone: +1 310 822 1511
   Paul Vixie
   Internet Software Consortium
   Star Route Box 159A
   Woodside, CA 94062
   Phone: +1 415 747 0204

Manning & Vixie Informational [Page 7]

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