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Network Working Group                                         B. ManningRequest for Comments: 2010                                           ISICategory: Informational                                         P. Vixie                                                                     ISC                                                            October 1996Operational Criteria for Root Name ServersStatus 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.Abstract   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.Manning & Vixie              Informational                      [Page 1]

RFC 2010                    DNSSVR Criteria                 October 1996   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.Manning & Vixie              Informational                      [Page 2]

RFC 2010                    DNSSVR Criteria                 October 1996   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 tosection 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.Manning & Vixie              Informational                      [Page 3]

RFC 2010                    DNSSVR Criteria                 October 1996     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.Manning & Vixie              Informational                      [Page 4]

RFC 2010                    DNSSVR Criteria                 October 1996     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   master.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   Seesection 2.7.5 - References   [RFC1035]      Mockapetris, P., "Domain Names - Implementation and Specification",      STD 13,RFC 1035, USC/Information Sciences Institute, November      1987.   [Postel96]      Postel, J., "New Registries and the Delegation of International Top      Level Domains", Work in Progress.   [IXFR]      Ohta, M., "Incremental Zone Transfer",RFC 1995, August 1996.   [NOTIFY]      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 19967 - Authors' Addresses     Bill Manning     USC/ISI     4676 Admiralty Way     Marina del Rey, CA 90292     Phone: +1 310 822 1511     EMail: bmanning@isi.edu     Paul Vixie     Internet Software Consortium     Star Route Box 159A     Woodside, CA 94062     Phone: +1 415 747 0204     EMail: paul@vix.comManning & Vixie              Informational                      [Page 7]