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RFC 433 UNKNOWN SOCKETS · SERVICES

Socket number list

Well-known socket numbers that early ARPANET computers agreed to use for standard services.

On rfc-editor.org ↗
PUBLISHED
December 1972
AUTHORS
J. Postel
STREAM
Legacy
BUILDS ON
RFC 349 — Proposed Standard Socket Numbers
OBSOLETED BY
RFC 503 — Socket number list
TELNET SOCKET
1
FILE TRANSFER SOCKET
3
ECHO SOCKET
7
STANDARD FUNCTION RANGE
0-63
DOI
10.17487/RFC0433
LINEAGE · FROM THE RFC INDEXOpen full graph →
'72RFC 349Proposed Standard Socket Numbers'72RFC 433Socket number list'73RFC 503Socket number list

RFC text

Original text · RFC Editor View on rfc-editor.org ↗ 
Network Working Group                              Jon Postel (UCLA-NMC)
Request for Comments: 433                             Nancy Neigus (BBN)
NIC 13491                                               22 December 1972
Categories: Socket Numbers
References: 349

                       Socket Number List


The czar of socket numbers [Jon Postel] has established the
following assignments for socket numbers used for public
functions. Note that a socket number is a 40 bit quantity, the
first 8 bits being the host specification, the next 24 bits being
site specific, and the last 8 bits being user specified - these
last 8 bits are called the AEN [it stands for, cleverly enough,
Another Eightbit Number].

For the assignments here the value in the host field ranges
across all hosts (unless otherwise specified), the value in the
24 bit field is zero, and the AEN is indicated here.

General Assignments:

       Sockets         Assignment

       0 - 63          Network Wide Standard Functions
       64 - 127        Host Specific Functions
       128 - 239       Reserved for Future Use
       240 - 255       Any Experimental Function


Particular Assignments:

       Socket          Assignment

       1               Telnet
       3               File Transfer
       5               Remote Job Entry
       7               Echo
       9               Discard
       19              Character Generator [e.g. TTYTST]

       65              Speech Data Base @ ll-tx-2 (74)
       67              Datacomputer @ cca (31)

       241             NCP Measurement
       243             Survey Measurement
       245             LINK

The specifications for the assigned functions can be found in the
documents listed here:

               Telnet                  RFC 318
               File Transfer           RFC 354 & RFC 385
               Remote Job Entry        RFC 407
               Echo                    RFC 347
               Discard                 RFC 348
               Character Generator     RFC 429
               Speech Data Base        SUR 37
               Datacomputer            [Murray @ CCA]
               NCP Measurment          RFC 388
               Survey Data             [Kampe @ NMC]
               LINK                    [Bressler @ BBN]


It has come to our attention that there are several hosts
performing useful public services on sockets which conflict with
the above scheme. We hope we can resolve this problem with a
minimum of disruption.

The following is a tabulation of socket numbers together with the
services offered. This listing is presented as an aid to network
users. If you know of a socket/function which has been left out
or an entry which should be corrected or deleted please contact:

                       Jon Postel
                       3804 Boelter Hall
                       Computer Science Department
                       University of California
                       Los Angeles, CA. 90024

                       Phone: (213) 825-2368

                       NIC Ident = JBP

                               or

                       Nancy Neigus
                       Bolt Beranek and Newman
                       50 Moulton Street
                       Cambridge, Mass. 02139

                       Phone: (617) 661-0100

                       NIC Ident = NJN

We will be pleased to include socket/function information for
other than "offical" sockets [e.g Tip News].

   1   UCLA-NMC
      1   Telnet
      241 NCP Measurement
      243 Survey Data
   2    SRI-ARC
      1    Telnet
      3    File Transfer
      5    Echo
      7    CPYNET
      9    SYSTAT
      13   DATE-TIME
   3    UCSB
      1    Telnet
      5    UCSB RJS [not ARPANET standard]
      7    Echo
      9    Discard
   4    UTAH
      1    Telnet
      3    File Transfer
      5    Echo
      7    CPYNET
      9    SYSTAT
      13   DATE-TIME
   5    NCC
   6    MIT-Multics
      1    Telnet
   9   Harvard
      1    Telnet
      3    Sorry File Transfer
   10   LL-67
      1    Telnet
   11   SAIL
      1    Telnet
      3    File Transfer
   12   ILL-ANTS
   13   CASE
      1    Telnet
      3    File Transfer
      5    Echo
      7    CPYNET
      9    SYSTAT
      13   DATE-TIME
   14   CMU
      1    Telnet
      3    File Transfer
   15   ILLIAC-TENEX
      1    Telnet
      3    File Transfer
      5    Echo
      7    CPYNET
      9    SYSTAT
      13   DATE-TIME
   16   NASA-AMES
      1    Telnet
      3    File Transfer
      5    Sorry Remote Job Entry
      7    Echo
      9    Discard
      241 NCP Measurement
   23   USC-44
   31   CCA-TENEX
      1    Telnet
      3    File Transfer
      5    Echo
      9    SYSTAT
      11   NETSTAT
   35   UCSD
      1    Telnet
   65   UCLA-CCN
      1    Telnet
      7    Echo
      9    Discard
      11   NETPJS [EBCDIC]
      13   NETRJS [ASCII]
      15   NETRJS [TTY]
   66   SRI-AI
      1    Telnet
      3    DATE-TIME
      5    Echo
      7    CPYNET
      9    SYSTAT
      11   Sorry NETSTAT
   69   BBN-TENEX (a)
      1    Telnet
      3    File Transfer
      5    Echo
      7    CPYNET
      9    SYSTAT
      13   DATE-TIME
      15   NETSTAT
      17   Oneliners
      3604505 = x'370019' = o'15600031'   TIP News
   70   MIT-DMCG
      1    Telnet
      3    File Transfer
      7    Network Status
      9    Discard
   74   LL-TX-2
      1    Telnet
   78   CMU-alt
      1    Telnet
      3    File Transfer
   86   ISI-TENEX
      1    Telnet
      3    File Transfer
      5    Echo
      7    CPYNET
      9    SYSTAT
      13   DATE-TIME
   133  BBN-TENEXB
      1    Telnet
      3    File Transfer
      5    Echo
      7    CPYNET
      9    SYSTAT
      13   DATE-TIME
      15   NETSTAT
      17   Oneliners
   134  MIT-AI
      1    Telnet
      3    File Transfer
   198  MIT-Mathlab
      1    Telnet
      3    File Transfer

Following hosts not tested

   7    RAND
   8    SDC-ADEPT
   19   NBS-ANTS
   138  LL-TSP





     [ This RFC was put into machine readable form for entry ]
      [ into the online RFC archives by James Carlson 11/98 ]

AI ELI5

On this page
PROBLEMEarly ARPANET computers needed to know which numbered sockets to use for common services like Telnet, file transfer, and email, so clients could connect to the right service.
MECHANISMJon Postel established a numbering scheme: sockets 0-63 for network-wide standard functions, 64-127 for host-specific functions, 128-239 reserved, and 240-255 for experiments. The RFC assigns numbers to specific services like Telnet (socket 1), File Transfer (3), and Echo (7).
WHY IT MATTERSThis scheme became the standard for addressing services on the early ARPANET, though it was later replaced by the more flexible port concept in TCP/IP.

§1Socket Number Assignments

RFC 433 publishes the standard assignments for socket numbers used for public functions on the early ARPANET. Jon Postel, designated the czar of socket numbers, established a 40-bit addressing scheme where the first 8 bits identified the host, the next 24 bits were site-specific, and the final 8 bits (called the AEN, Another Eightbit Number) identified the specific service.

The RFC defines ranges for different categories of services and assigns numbers to well-known functions that all ARPANET sites could use.

A socket number is like a room number in a big office building. The first digits say which building, the last digits say what service is there.

§2Socket Number Ranges

The numbering scheme divides socket space into regions: sockets 0-63 are Network Wide Standard Functions available on all hosts, sockets 64-127 are Host Specific Functions, sockets 128-239 are reserved for future use, and sockets 240-255 are open for experimental functions.

Well-known services include Telnet (1), File Transfer (3), Remote Job Entry (5), Echo (7), Discard (9), and Character Generator (19). Some sockets like 241 (NCP Measurement) and 243 (Survey Measurement) serve network operations.

Low numbers like 1, 3, and 7 are for everyone to use. Higher numbers are for experiments or special sites.

§3Deployed Services

The RFC also lists actual services running on various ARPANET hosts using these sockets. UCLA-NMC offers Telnet (1) and measurement sockets (241, 243). SRI-ARC offers Telnet (1), File Transfer (3), Echo (5), CPYNET (7), and SYSTAT (9). BBN-TENEX and other major sites offer Telnet, File Transfer, and various network utilities on assigned sockets.

The RFC notes that some hosts run services on non-standard socket numbers and requests operators to report any missing or incorrect entries.

Different computers on the network offer different services on these numbered sockets, and the RFC lists which ones actually work.

§4Status Today

This RFC was replaced by RFC 503. The socket numbering scheme later evolved into the port concept in TCP/IP, which is still used today in modern networks.

This system of assigning service numbers got updated later, and the basic idea became how modern networks work.

§5References

[1]RFC 503Postel, J. and N. Neigus, "Socket Number List", RFC 503, December 1972.April 1973