Network Working Group J. Postel
Request for Comments: 881 ISI
 November 1983
 The Domain Names Plan and Schedule
This RFC outlines a plan and schedule for the implementation of domain
style names throughout the DDN/ARPA Internet community. The
introduction of domain style names will impact all hosts on the DDN/ARPA
Internet.
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.
RFC 881 November 1983
The 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.
RFC 881 November 1983
The 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.
RFC 881 November 1983
The 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.
RFC 881 November 1983
The 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" and
RFC 881 November 1983
The 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 the
RFC 881 November 1983
The 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.
RFC 881 November 1983
The Domain Names Plan and Schedule 
The 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.]
RFC 881 November 1983
The 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 example
RFC 881 November 1983
The 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.