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Network Working Group                                          J. PostelRequest for Comments: 881                                            ISI                                                           November 1983The Domain Names Plan and ScheduleThis RFC outlines a plan and schedule for the implementation of domainstyle names throughout the DDN/ARPA Internet community.  Theintroduction of domain style names will impact all hosts on the DDN/ARPAInternet.The Plan   Introduction      Domain style names are being introduced in the Internet to allow a      controlled delegation of the authority and responsibility for      adding hosts to the system.  This also allows a subdivision of the      task of maintaining information about hosts.      The subdivision will be based on administrative authority or      organization boundaries (not necessarily network boundaries).      Certain requirements will be placed on organizations wishing to be      "top level" domains.  Initially, all the hosts in the Internet      will be in the domain "ARPA".  As soon as is practical a second      domain, "DDN", will be introduced.  Other domains may be added      after that, provided the requirements listed below are met.      Domain names will be supported in the long run by a system of      special servers called "domain servers" which will be used to      translate names to addresses.  While this system of domain servers      is being created and programs are being converted to use them, the      existing host tables will evolve to include domain style names.      The domain server design also provides for mapping mailbox      addresses to the host name of the mail server for that mailbox.      This feature allows mailboxes to be related to an organization      rather than to a specific host.      This plan will be implemented in the ARPA community.  After the      domain system is demonstrated in the ARPA community, the DDN      Program Management Office (DDN-PMO) will determine the schedule      for implementation of the domain system in the DDN community.      This approach will cause some extra steps in the ARPA community      implementation, and may limit communication between the ARPA and      DDN communities in some ways.  The details and implications of      this two phase approach are discussed more fully below.Postel                                                          [Page 1]

RFC 881                                                    November 1983The Domain Names Plan and Schedule   A Catch 22      There is a problem in introducing domain style names: a great deal      of software has to be changed.  Some groups would like to start      using domain style names right away, and other groups don't want      to see them or use them for a very long time.  Communication      patterns are very complex and as soon as domain style names are      allowed and used by a few groups they will start showing up almost      everywhere.  This argues that everyone should be prepared for them      before they are used at all.  However, we know that with people      being people and with so many of people involved, the probability      of everyone being ready in any reasonable time period is nearly      zero.  The way out of this situation is to set up a reasonable      schedule for experimenting with domain style names and authorizing      their use.  People that get ready on schedule should have no      problems with these names.   Evolution of the Table      Nearly all the hosts in the Internet now use some form of host      table based on the master file "HOSTS.TXT" maintained by the      Network Information Center (NIC).      One way to introduce domain style names is to add to the entries      in this table names in the domain style.  In particular, make the      first name in each entry the official host name in the ARPA      domain.         For example, the current entry for USC-ISIF is:            HOST : 10.2.0.52 : USC-ISIF,ISIF : DEC-1090T : TOPS20 :            TCP/TELNET,TCP/SMTP,TCP/FTP,TCP/FINGER,UDP/TFTP :         This could become:            HOST : 10.2.0.52 : USC-ISIF.ARPA,USC-ISIF,ISIF : DEC-1090T :            TOPS20 : TCP/TELNET,TCP/SMTP,TCP/FTP,TCP/FINGER,UDP/TFTP :      For some hosts and programs this could be done today with no      disruptions, but for others substantial problems could occur.  For      example, with over five hundred entries in the table the addition      of 500 names could exceed the space allocated to store the table      in some programs.  (One could argue that these programs are going      to blow up soon anyway as new host entries are added to the      table.)  Another problem is that period (or dot, ".") is not now a      legal character in host names and some programs may not be able to      parse these new names.Postel                                                          [Page 2]

RFC 881                                                    November 1983The Domain Names Plan and Schedule      The plan is to make such a domain style name table available in      parallel with the regular table for a few months, then to replace      the regular table with this domain style table.  The dates for      these changes is given in the schedule below.      So far, no new domains have been introduced.  Only a table with      all the entries having official names in the ARPA domain has been      provided.  This should allow programs to be constructed to deal      with domain style names in a general way without any special hacks      to add or delete the string ".ARPA" to or from host names.      The introduction of new domains is tied to the provision of domain      servers by those domains.  As new domains meet the requirements      and are authorized they will also be added to the host table.  No      new domains will be added before master table is converted to the      domain style entries.      In the long run the Internet will become too complex and change      too fast to keep a master table of all the hosts.  At some point      the master table will be reduced to simply the entries for the      domain servers for the top level domains.  By this time all normal      translation of host names into addresses should take place by      consulting domain servers.   Conversion to Servers      As soon as domain servers become available programs should be      converted to use them to translate names into addresses.  The      details of these procedures are given in RFCs 882 and 883.      The general idea is that a host no longer keeps a complete host      table but rather makes a request on the domain server each time a      name must be translated to an address.  The code module in the      host that implements the protocol to do this is called a      "resolver".  The resolver may keep a cache of recently translated      names and addresses for improved performance.      Many hosts have a library function or system call that is used to      access the host table to translate names to addresses.  It ought      to be possible to replace this function or call with the resolver      module such that most programs would not know which method was      used to accomplish the name to address translation.Postel                                                          [Page 3]

RFC 881                                                    November 1983The Domain Names Plan and Schedule   Requirements on a Domain      There are several requirements that must be met to establish a      domain.  In general it must be responsibly managed.  There must be      a responsible person to serve as a coordinator for domain related      questions,  there must be a robust name service, it must be of at      least a minimum size,  and the domain must be registered with the      central domain administrator.      Responsible Person:         An individual must be identified who has authority for the         administration of the names within the domain, and who takes         responsibility for the behavior of the hosts in the domain in         their interactions with hosts outside the domain.         The operation of a name server should not be taken on lightly.         There are some difficult problems in providing an adequate         service, primarily the problems in keeping the data base up to         date, and keeping the service operating.         If some host in a domain somehow misbehaves in interactions         with hosts outside the domain (e.g., consistently violates         protocols), the responsible person for the domain must be able         to take action to eliminate the problem.      Domain Servers:         A robust and reliable domain service must be provided.  One way         of meeting this requirement is to provide at least two         independent domain servers for the domain.  The data base can,         of course, be the same.  The database can be prepared and         copied to each domain server.  But, the servers should be in         separate machines on independent power supplies, et cetera;         basically as physically independent as can be and yet in the         same domain.  They should have no common point of failure.         One of the difficult problems in operating a domain server is         the acquisition and maintenance of the data.  In this case the         data is the host names and addresses.  In some environments         this information changes fairly rapidly and keeping up-to-date         data may be difficult.  This is one motivation for sub-domains.         One may wish to create sub-domains until the rate of change of         the data in a sub-domain domain server data base is easily         managed.         The concepts and implementation details of the domain server         are given in RFCs 882 and 883.Postel                                                          [Page 4]

RFC 881                                                    November 1983The Domain Names Plan and Schedule      Minimum Size:         The domain must be of at least a minimum size.  Several         measures of size may be used in combination in making this         test.  Measures may include: (a) the number of host computers         in the domain, (b) the number of people with primary mailboxes         in the domain, (c) the amount of traffic that crosses the         boundary of the domain [packets/day or mail items/week].         Specific threshold values for these measures will be         established before new domains are authorized.         There is no requirement to form a domain because some set of         hosts is above the minimum size.      Registration:         The administrator must register the domain with the central         authority.  The central authority must be satisfied that the         requirements are met before authorization for the domain is         granted.         The administrator of a domain is required to make sure that         host and sub-domain names within that jurisdiction conform to         the standard name conventions and are unique with in that         domain.         If sub-domains are set up the administrator may wish to pass         along some of his authority and responsibility to a sub-domain         administrator.   Mailbox Support      The design of the domain servers provides two levels of support      for mail.      The first, called "agent binding", is that the right hand part of      the typical mail box (Y in X@Y) can be mapped a host that will      either accept the mail as the destination or accept the mail for      forwarding.      The second, called "mailbox binding", is to map the entire mailbox      (X@Y) to a destination (this mechanism can also support some      mailing list functions).      Agent binding can be used to establish mailboxes that are based on      an organization name rather than a host name.         For example, an organization, "BLAT", with hosts "BLAT-20" andPostel                                                          [Page 5]

RFC 881                                                    November 1983The Domain Names Plan and Schedule         "BLAT-VAX" in the ARPA domain could set up mailboxes of the         form "user@BLAT.ARPA" and use the domain server mechanisms for         mapping these to the host that accepts the mail for the         organization.      Mailbox binding will allow different mappings for individual      mailboxes of an organization or host to the destination host.  It      will also provide for aliases and mailing groups.         Mailbox binding requires adding information on individual         mailboxes to the domain server database.  This could be a         substantial increase in the database size and management         responsibility.   The ARPA Community and the DDN Community      This plan will be put into effect in the ARPA community.      The DDN community will adopt the domain style names, but will      continue with the present scheme of a centrally maintained table      copied periodically by each host.  Once the use of domain servers      has been demonstrated by use in the ARPA community, the DDN-PMO      will establish a schedule for implementing the domain system in      the DDN community.      This means that there may be a period of a year or more with the      two communities using different schemes for distributing      information about host names and addresses.      Specifically:         The NIC will maintain a table a "HOSTS.TXT" style table for use         by DDN hosts.  This table will contain domain style names for         all DDN hosts (e.g., USC-ISIA.DDN).  Since this is the only         information DDN hosts will use to translate host names to         Internet Addresses, this table must also contain names and         addresses of ARPA community hosts of interest to DDN users         (e.g., USC-ISIF.ARPA).         There will be a domain server with data for the DDN domain.         That is, hosts in the ARPA community that use the domain system         of resolvers and servers will be able to access servers that         have the data base covering the DDN community.      It is quite likely that the table for the use of the DDN hosts      will be incomplete with respect to coverage of the ARPA community      and any new domains that are established.  One motivation for the      domain system is the subdivision of name management to avoid thePostel                                                          [Page 6]

RFC 881                                                    November 1983The Domain Names Plan and Schedule      difficulty of keeping a global table of all hosts.  As the ARPA      community moves to significant use of the domains system the      maintenance of a global table for use by the DDN community will      become very difficult.      This means that DDN hosts might not be able to look up the names      of some ARPA community hosts in their local tables.  In some cases      this might result in an inability establish communication from a      DDN hosts to such "unknown" ARPA community hosts.         The most likely case is for a computer mail message sent from         an ARPA community user on a host know to name servers but not         in the central table to a user on a DDN community host that         relies on a local copy of the central table.  When the DDN user         attempts to answer this message his mail program will attempt         to look up the host name.  This will fail, and the most likely         result is that the mail program will tell the user that there         is no such host!      Please note that DDN community hosts are permitted (even      encouraged) to implement the domain system in parallel with the      ARPA community.  However, there is no requirement that they do so      until called for in the schedule to be established by the DDN-PMO.Postel                                                          [Page 7]

RFC 881                                                    November 1983The Domain Names Plan and ScheduleThe Schedule   04-Oct-83  The ARPANET/MILNET Logical Split   02-Nov-83  Publish Domain Name Documents      This Plan and Schedule (RFC-881), Domain Names - Concepts and      Facilities (RFC-882), and Domain Names - Implementation      Specification (RFC-883).   16-Nov-83  Make Available Domain Style Host Table      Create a copy a modified version of the HOSTS.TXT table named      DHOSTS.TXT with an additional name (as the first name) in each      entry of the form "official-host-name.ARPA".   15-Dec-83  Final Specification of simple Query & Reply Protocol   Available      This specification covers the protocol procedures and message      formats for the simple queries and replies to support translating      host names to internet addresses only.   15-Dec-83  Make Limited Domain Server & Resolvers Available      An example limited domain server running on TOPS-20 and example      limited resolvers running on each of TOPS-20 and VAX-Berkeley-Unix      should be made available for testing and copying.  This simple      version would be able to do queries and responses for host name to      internet address translation only, and the servers would still use      the global table.  This simple server would not refer the resolver      to another server.  This simple server and these resolvers operate      in datagram mode only.  However, this would allow user programs to      begin to use the servers.   01-Feb-84  Specification of Domain Requirements Available      Detailed requirements for qualifying a set of hosts as a domain,      and procedure for registering new domains is published.   15-Feb-84  The ARPANET/MILNET Access Controls      MILNET access controls installed in the MILNET/ARPANET gateways      and TAC user access controls put into effect (see DDN MGT Bulletin      16). [Date approximate.]Postel                                                          [Page 8]

RFC 881                                                    November 1983The Domain Names Plan and Schedule   07-Mar-84  Replace Main Host Table with Domain Style Host Table      The DHOSTS.TXT becomes HOSTS.TXT.   14-Mar-84  Final Specification of Query & Reply Protocol Available      This specification covers the protocol procedures and message      formats for the all queries and replies between resolvers and      servers.   14-Mar-84  Make Improved Domain Servers & Resolvers Available      An example improved domain server running on TOPS-20 and example      improved resolvers running on each of TOPS-20 and      VAX-Berkeley-Unix should be made available for testing and      copying.  This version should be able to do any of the defined      query and response operations, and should support segmented data      base by refering resolvers to other servers if necessary.  This      server loads zone data from local master files only, and only at      program start up.  This server and these resolvers operate with      either datagram or reliable connection style communication.  This      version does not support the data base update portion of the      server protocol.   04-Apr-84  Domain Servers for ARPA Domain Available      Authoritative domain servers for the ARPA domain will be available      for regular use.   02-May-84  Introduce New Domains in the Main Host Table      Add the DDN domain.  Most MILNET hosts will change to the DDN      domain.  Authoritative domain servers for the DDN domain will be      available for regular use.  HOSTS.TXT is updated.   02-May-84  Establish a New Top Level Domains Only Table      Start a new table, DOMAINS.TXT, that lists only the top level      domains and the entries for their domain servers.   16-May-84  Final Specification of Maintenance Protocol Available      This specification covers the protocol procedures and message      formats for the data base update exchanges between servers.   16-May-84  Make Improved Domain Servers & Resolvers Available      An example improved domain server running on TOPS-20 and examplePostel                                                          [Page 9]

RFC 881                                                    November 1983The Domain Names Plan and Schedule      improved resolvers running on each of TOPS-20 and      VAX-Berkeley-Unix should be made available for testing and      copying.  This version should be able to do any of the defined      query and response operations, and should support segmented data      base by refering resolvers to other servers if necessary.  This      server loads zone data from local master files and remote servers,      and only at program start up.  This server and these resolvers      operate with either datagram or reliable connection style      communication.   06-Jun-84  Permit the Introduction of New Domains      Organizations meeting the requirements for establishing new      domains will be allowed to begin use of new domain names.  New      domains must be registered, meet the requirements (including      running domain servers), and will be added to the HOSTS.TXT table.   18-Jul-84  Final Specification of Complete Protocol Available      This specification covers the protocol procedures and message      formats for the complete domain names system.   18-Jul-84  Make Full Domain Servers & Resolvers Available      At this point an example domain server and an example resolver      running on each of TOPS-20 and VAX-Berkeley-Unix should be made      available for testing and copying.  This version should be able to      do any of the defined query and response operations, and should      support segmented data base by refering resolvers to other servers      if necessary.  This version should support the data base update      portion of the server protocol, including data aging and dynamic      zone updating from remote servers.  This is a full implementation      of the protocol.   05-Sep-84  Discontinue the Full Host Table for the ARPA Community      Stop maintaining the HOSTS.TXT table for the ARPA community.  The      HOSTS.TXT table continues to be used in the DDN community with      complete data for the DDN domain, however the data for the ARPA      and other domains may no longer be complete or fully up to date.   03-Oct-84  DDN-PMO Schedules DDN Implementation      The DDN-PMO establishes the schedule for the implementation of the      domain system in the DDN community.Postel                                                         [Page 10]