RFC 840

Official protocols

📅 published April 1983, from ietf

Official Protocols 🎀

okay bestie, this is RFC 840, and it's giving 1983 💅 It was written by J. Postel at ISI and dated April 1983, in the Network Working Group. The header doesn't list a category, and it doesn't say what it obsoletes or updates. Its whole job is to be the official list of which documents define the Internet's protocols, plus notes on any changes that were planned. Think of it as the "who's who" of the early internet 🦋

So the basic idea: to first order, the official protocols are the ones in the Internet Protocol Transition Workbook (IPTW) from March 1982. Some protocols in use aren't in the IPTW, though, and a few IPTW protocols got revised, which the document notes. The mail protocols got their own volume, "Internet Mail Protocols", dated November 1982. There's also the Internet Protocol Implementers Guide (IPIG), dated August 1982, for extra protocol info. And some protocols, especially the Telnet Options, haven't been touched in years, so they live in the old ARPANET Protocol Handbook (APH) from January 1978 🧚

This doc is organized like a sketchy outline 📝 Each entry is a protocol, like Transmission Control Protocol, and every entry has notes on status, specification, comments, other references, dependencies, and contact:

Status is one of: required, recommended, elective, or experimental.
Specification names the documents that define the protocol.
Comments cover differences from the spec or problems with the protocol.
Other references list docs that comment on or expand on the protocol.
Dependencies list the other protocols this one calls on.
Contact is a person who can answer questions about the protocol.

The status needs a little more explaining, so here's the tea ☕

required: all hosts must implement the required protocol.
recommended: all hosts are encouraged to implement the recommended protocol.
elective: hosts may implement or not the elective protocol.
experimental: hosts should not implement the experimental protocol unless they are participating in the experiment and have coordinated their use of this protocol with the contact person.
none: this is not a protocol.

Overview

Catenet Model

STATUS: None

SPECIFICATION: IEN 48 (in IPTW)

COMMENTS:

This one gives an overview of how the Internet is organized and the principles behind it ✨ It could be revised and expanded, so there's room for a glow-up.

OTHER REFERENCES: (none listed)

DEPENDENCIES: (none listed)

CONTACT: Postel@USC-ISIF

Network Level

Internet Protocol (IP)

STATUS: Required

SPECIFICATION: RFC 791 (in IPTW)

COMMENTS:

A few minor problems have been noted in this document, but the big one is confusion in the route options 🙈 Route options have a pointer that says which octet of the route is next to be used. The confusing part is between the phrases "the pointer is relative to this option" and "the smallest legal value for the pointer is 4". If you're confused, just forget about the relative part, because the pointer begins at 4.

Another important point is the alternate reassembly procedure suggested in RFC 815.

Also, ICMP is officially part of IP. You haven't completed an implementation of IP if it doesn't include ICMP 💀

OTHER REFERENCES:

RFC 815 (in IPIG) - IP Datagram Reassembly Algorithms
RFC 814 (in IPIG) - Names, Addresses, Ports, and Routes
RFC 816 (in IPIG) - Fault Isolation and Recovery
RFC 817 (in IPIG) - Modularity and Efficiency in Protocol Implementation

DEPENDENCIES: (none listed)

CONTACT: Postel@USC-ISIF

Internet Control Message Protocol (ICMP)

STATUS: Required

SPECIFICATION: RFC 792 (in IPTW)

COMMENTS:

A few minor errors in the document have been noted. People also suggested extra types of redirect message and extra destination unreachable messages, so ICMP has some main-character potential 🌈

OTHER REFERENCES: (none listed)

DEPENDENCIES: Internet Protocol

CONTACT: Postel@USC-ISIF

Host Level

User Datagram Protocol (UDP)

STATUS: Recommended

SPECIFICATION: RFC 768 (in IPTW)

COMMENTS:

The only change noted for the UDP spec is a small clarification. If a padding octet is used when computing the checksum, it isn't transmitted and it isn't counted in the length. Tiny detail, big vibes 🫶

OTHER REFERENCES: (none listed)

DEPENDENCIES: Internet Protocol

CONTACT: Postel@USC-ISIF

Transmission Control Protocol (TCP)

STATUS: Recommended

SPECIFICATION: RFC 793 (in IPTW)

COMMENTS:

Okay, TCP got SO many comments and corrections 😭 Most of them are document bugs rather than protocol bugs, so the protocol itself is fine, the writing just needs a little love.

Here's the list of what needs fixing:

Event Processing Section: There are many minor corrections and clarifications needed in this section.
Push: Some phrases still give a "record mark" flavor to the push. These should be clarified further. The push is not a record mark.
Listening Servers: Several comments came in about difficulties contacting listening servers. There should be some discussion of implementation issues for servers, plus some notes on alternative models of system and process organization for servers.
Maximum Segment Size: The maximum segment size option should be generalized and clarified. It can be used to either increase or decrease the maximum segment size from the default, and the default should be established more clearly. The default is based on the default maximum Internet Datagram size, which is 576 octets counting the IP and TCP headers. The option counts only the segment data. For each of IP and TCP, the minimum header is 20 octets and the maximum header is 60 octets. So the default maximum data segment could be anywhere from 456 to 536 octets. The current proposal is to set it at 536 data octets 🎀
Idle Connections: People asked about automatically closing idle connections. The answer is that idle connections are ok and should not be closed. Idle connections happen in several cases, for example in Telnet when a user is thinking for a long time after a message from the server computer before their next input. There is no TCP "probe" mechanism, and none is needed.
Queued Receive Data on Closing: In several places it isn't clear what to do with data the TCP has received but not yet passed to the user, especially when the connection is closing. In general, the data is to be kept so it can be given to the user if they do a RECV call.
Out of Order Segments: The description says segments that arrive out of order (meaning not exactly the next segment to be processed) may be kept on hand. It should also point out that there's a very large performance penalty for not doing so. Don't skip this one, bestie 💖
User Time Out: This is the time out started on an open or send call. If it occurs, the user should be notified, but the connection should not be closed and the TCB should not be deleted. If the user wants to give up, they should explicitly ABORT the connection.

OTHER REFERENCES:

RFC 813 (in IPIG) - Window and Acknowledgement Strategy in TCP
RFC 814 (in IPIG) - Names, Addresses, Ports, and Routes
RFC 816 (in IPIG) - Fault Isolation and Recovery
RFC 817 (in IPIG) - Modularity and Efficiency in Protocol Implementation

DEPENDENCIES: Internet Protocol

CONTACT: Postel@USC-ISIF

Host Monitoring Protocol (HMP)

STATUS: Elective

SPECIFICATION: IEN 197

COMMENTS:

This is a good tool for debuging protocol implementations in small remotely located computers 🔥 It's also used to monitor Internet gateways and the TACs.

OTHER REFERENCES: (none listed)

DEPENDENCIES: Internet Protocol

CONTACT: Hinden@BBN-UNIX

Cross Net Debugger (XNET)

STATUS: Elective

SPECIFICATION: IEN 158

COMMENTS:

This specification should be updated and reissued as an RFC. Hello, glow-up era 🌸

OTHER REFERENCES:

RFC 643

DEPENDENCIES: Internet Protocol

CONTACT: Postel@USC-ISIF

Exterior Gateway Protocol (EGP)

STATUS: Experimental

SPECIFICATION: RFC 827

COMMENTS:

Please discuss any plans for implementation or use of this protocol with the contact 🧚

OTHER REFERENCES: (none listed)

DEPENDENCIES: Internet Protocol

CONTACT: Postel@USC-ISIF

      Number   Name                                   RFC   NIC  APH USE
      ------   ------------------------------------   ---  ----- --- ---
         0     Binary Transmission                    ...  15389 yes yes
         1     Echo                                   ...  15390 yes yes
         2     Reconnection                           ...  15391 yes  no
         3     Suppress Go Ahead                      ...  15392 yes yes
         4     Approximate Message Size Negotiation   ...  15393 yes  no
         5     Status                                 651  31154 yes yes
         6     Timing Mark                            ...  16238 yes yes
         7     Remote Controlled Trans and Echo       726  39237 yes  no
         8     Output Line Width                      ...  20196 yes  no
         9     Output Page Size                       ...  20197 yes  no
        10     Output Carriage-Return Disposition     652  31155 yes  no
        11     Output Horizontal Tabstops             653  31156 yes  no
        12     Output Horizontal Tab Disposition      654  31157 yes  no
        13     Output Formfeed Disposition            655  31158 yes  no
        14     Output Vertical Tabstops               656  31159 yes  no
        15     Output Vertical Tab Disposition        657  31160 yes  no
        16     Output Linefeed Disposition            658  31161 yes  no
        17     Extended ASCII                         698  32964 yes  no
        18     Logout                                 727  40025 yes  no
        19     Byte Macro                             735  42083 yes  no
        20     Data Entry Terminal                    732  41762 yes  no
        21     SUPDUP                             734 736  42213 yes  no
        22     SUPDUP Output                          749  45449  no  no
        23     Send Location                          779  -----  no  no
       255     Extended-Options-List                  ...  16239 yes yes

STATUS: Elective 🌸

SPECIFICATION: (in APH)

COMMENTS:

Okay so there's an open question about some of these. ngl most of the options are only implemented by like, a handful of hosts, so maybe they should just be eliminated. 🙈 They all need to be studied, and the useful ones should be reissued as RFCs. ✨

The USE column in the table above shows which options are in general use. 💅

These are the recommended ones: Binary Transmission, Echo, Suppress Go Ahead, Status, Timing Mark, and Extended Options List. 🫶

A lot of these will need revising before they work with TCP. 🦋

OTHER REFERENCES: none listed

DEPENDENCIES: Telnet

CONTACT: Postel@USC-ISIF

File Transfer Protocol (FTP) 📂

STATUS: Recommended 💖

SPECIFICATION: RFC 765 (in IPTW)

COMMENTS:

There are a bunch of minor corrections to make. The big changes are deleting the mail commands, and clarifying how the data connection is managed, which is badly needed. 😭 There's also a suggestion to add some directory manipulation commands (RFC 775). 🗂️

Even though the MAIL features are defined in this document, they are not to be used. SMTP is the protocol to use for all mail service in the Internet. 📬

Data Connection Management:

a. Default Data Connection Ports: All FTP implementations must support use of the default data connection ports, and only the User-PI may initiate the use of non-default ports. 🔒
b. Negotiating Non-Default Data Ports: The User-PI may specify a non-default user side data port with the PORT command. The User-PI may ask the server side to identify a non-default server side data port with the PASV command. Since a connection is defined by the pair of addresses, either of these actions is enough to get a different data connection. Still, it is permitted to do both commands to use new ports on both ends of the data connection. 🎀
c. Reuse of the Data Connection: When using the stream mode of data transfer, the end of the file must be indicated by closing the connection. This causes a problem if multiple files are going to be transferred in the session, because TCP has to hold the connection record for a time out period to guarantee reliable communication. So the connection can not be reopened right away. 😤

There are two solutions to this problem. The first is to negotiate a non-default port (as in (b) above). The second is to use another transfer mode. 🧚

A comment on transfer modes: the stream transfer mode is inherently unreliable, because you can't tell whether the connection closed prematurely or not. The other transfer modes (Block, Compressed) don't close the connection to indicate end of file. They have enough FTP encoding that the data connection can be parsed to find the end of the file. So with these modes, you can leave the data connection open for multiple file transfers. 🦋

Why this was not a problem with the old NCP FTP:

The NCP was designed with only the ARPANET in mind. The ARPANET provides very reliable service, and the NCP counted on it. If any packet of data from an NCP connection was lost or damaged by the network, the NCP could not recover. It is a tribute to the ARPANET designers that the NCP FTP worked so well. 👑

TCP is designed to provide reliable connections over many different types of networks and interconnections of networks. TCP has to cope with a set of networks that can not promise to work as well as the ARPANET. TCP must make its own provisions for end-to-end recovery from lost or damaged packets. This is why the connection phase-down time-out is needed. The NCP never had to deal with acknowledgements, retransmissions, or many other things TCP must do to make a connection reliable in a more complex world. 🌈

LIST and NLST:

There's some confusion about the LIST and NLST commands, and about what is appropriate to return. Some clarification and motivation for these commands should be added to the specification. 🤔

OTHER REFERENCES:

RFC 678 - Document File Format Standards 📚

DEPENDENCIES: Transmission Control Protocol

CONTACT: Postel@USC-ISIF

Trivial File Transfer Protocol (TFTP) 🍓

STATUS: Elective ✨

SPECIFICATION: RFC 783 (in IPTW)

COMMENTS:

No known problems with this specification. It's in use in several local networks. 💜

OTHER REFERENCES: none listed

DEPENDENCIES: User Datagram Protocol

CONTACT: Postel@USC-ISIF

Simple Mail Transfer Protocol (SMTP) 💌

STATUS: Recommended 💖

SPECIFICATION: RFC 821

COMMENTS:

This has been revised since the IPTW. It's in the "Internet Mail Protocols" volume of November 1982. RFC 788 (in IPTW) is obsolete. 🍒

There were lots of misunderstandings and errors in the early implementations. Some documentation of these problems can be found in the file [ISIF]<SMTP>MAIL.ERRORS. 🙈

Some minor differences between RFC 821 and RFC 822 should be resolved. 🫠

OTHER REFERENCES:

RFC 822 - Mail Header Format Standards

This has been revised since the IPTW. It's in the "Internet Mail Protocols" volume of November 1982. RFC 733 (in IPTW) is obsolete. Further revision of RFC 822 is needed to correct some minor errors in the details of the specification. ✉️

DEPENDENCIES: Transmission Control Protocol

CONTACT: Postel@USC-ISIF

Remote Job Entry (RJE) 🖨️

STATUS: Elective 🌷

SPECIFICATION: RFC 407 (in APH)

COMMENTS:

Some changes are needed for use with TCP. 🛠️

No known active implementations. 🥲

OTHER REFERENCES: none listed

DEPENDENCIES: File Transfer Protocol, Transmission Control Protocol

CONTACT: Postel@USC-ISIF

Remote Job Service (NETRJS) 🧾

STATUS: Elective 🌸

SPECIFICATION: RFC 740 (in APH)

COMMENTS:

Used with the UCLA IBM OS system. 💻

Please discuss any plans for implementing or using this protocol with the contact. 💬

Revision in progress. 🚧

OTHER REFERENCES: none listed

DEPENDENCIES: Transmission Control Protocol

CONTACT: Braden@USC-ISIA

Remote Telnet Service 🔌

STATUS: Elective 🌼

SPECIFICATION: RFC 818

COMMENTS: none listed

OTHER REFERENCES: none listed

DEPENDENCIES: Telnet, Transmission Control Protocol

CONTACT: Postel@USC-ISIF

Graphics Protocol 🎨

STATUS: Elective 🩷

SPECIFICATION: NIC 24308 (in APH)

COMMENTS:

Very minor changes are needed for use with TCP. ✨

No known active implementations. 🥺

OTHER REFERENCES: none listed

DEPENDENCIES: Telnet, Transmission Control Protocol

CONTACT: Postel@USC-ISIF

Echo Protocol 🪞

STATUS: Recommended 💖

SPECIFICATION: RFC 347

COMMENTS:

This specification should be revised for use with TCP and reissued. 🔁

OTHER REFERENCES: none listed

DEPENDENCIES: Transmission Control Protocol or User Datagram Protocol

CONTACT: Postel@USC-ISIF

Discard Protocol 🗑️

STATUS: Elective 🌙

SPECIFICATION: RFC 348

COMMENTS:

This specification should be revised for use with TCP and reissued. 🔁

OTHER REFERENCES: none listed

DEPENDENCIES: Transmission Control Protocol or User Datagram Protocol

CONTACT: Postel@USC-ISIF

Character Generator Protocol 🔤

STATUS: Elective 🎀

SPECIFICATION: RFC 429

COMMENTS:

This specification should be revised for use with TCP and reissued. 🔁

OTHER REFERENCES: none listed

DEPENDENCIES: Transmission Control Protocol or User Datagram Protocol

CONTACT: Postel@USC-ISIF

Quote of the Day Protocol 💬

STATUS: Elective 🌟

SPECIFICATION: RFC xxx

COMMENTS:

Open a connection to this server. It sends you a quote (as a character string) and closes the connection. This should be described in an RFC. 📝

OTHER REFERENCES: none listed

DEPENDENCIES: Transmission Control Protocol or User Datagram Protocol

CONTACT: Postel@USC-ISIF

Active Users Protocol 👀

STATUS: Elective 🦄

SPECIFICATION: RFC xxx

COMMENTS:

Open a connection to this server. It sends you a list of the currently logged in users (as a character string) and closes the connection. This should be described in an RFC. 📝

OTHER REFERENCES: none listed

DEPENDENCIES: Transmission Control Protocol or User Datagram Protocol

CONTACT: Postel@USC-ISIF

Finger Protocol 🖐️

STATUS: Elective 🌸

SPECIFICATION: RFC 742 (in APH)

COMMENTS:

Some extensions have been suggested. 💡

Some changes are needed for TCP. 🛠️

OTHER REFERENCES: none listed

DEPENDENCIES: Transmission Control Protocol

CONTACT: Postel@USC-ISIF

NICNAME Protocol 🪪

STATUS: Elective 💜

SPECIFICATION: RFC 812 (in IPTW)

COMMENTS:

Okay so this one is the ARPANET directory lookup thing 📇 It accesses the ARPANET Directory database 💖

OTHER REFERENCES: (nothing listed) DEPENDENCIES: Transmission Control Protocol CONTACT: Feinler@SRI-NIC 🧚

HOSTNAME Protocol 🌸

STATUS: Elective SPECIFICATION: RFC 811 (in IPTW) ✨ COMMENTS: It accesses the Registered Internet Hosts database, aka HOSTS.TXT 📄 OTHER REFERENCES: RFC 810 - Host Table Specification DEPENDENCIES: Transmission Control Protocol CONTACT: Feinler@SRI-NIC

Host Name Server Protocol 💀

STATUS: Experimental SPECIFICATION: IEN 116 (in IPTW) COMMENTS: Okay, bestie, this spec has some significant problems 😭

The name syntax is out of date. 🙈
The protocol details are ambiguous. In particular, the length octet either does or doesn't include itself and the op code. Literally which one?? 💀
The extensions are not supported by any known implementation. Not one. 🫠

Work is in progress on a significant revision 🛠️ Further implementations of this protocol are not advised, so please don't go building new stuff on it. 🚫

Please discuss any plans for implementation or use of this protocol with the contact. 💌

OTHER REFERENCES: (nothing listed) DEPENDENCIES: User Datagram Protocol CONTACT: Postel@USC-ISIF 👑

CSNET Mailbox Name Server Protocol 🎀

STATUS: Experimental SPECIFICATION: CS-DN-2 COMMENTS: Same energy as before: if you have plans to implement or use this protocol, talk to the contact first 🫶 OTHER REFERENCES: (nothing listed) DEPENDENCIES: Transmission Control Protocol CONTACT: Solomon@UWISC 🦋

Daytime Protocol ☀️

STATUS: Elective SPECIFICATION: RFC xxx 🙃 COMMENTS: This one is super simple. You open a connection to the server, it sends you the date and time as a character string, and then it closes the connection. Iconic. 💅 It should be described in an RFC, but for now the RFC is still RFC xxx, so it's giving placeholder energy 😭

OTHER REFERENCES: (nothing listed) DEPENDENCIES: Transmission Control Protocol or User Datagram Protocol CONTACT: Postel@USC-ISIF 💜

Time Server Protocol ⏰

STATUS: Recommended 🌈 SPECIFICATION: IEN 142 COMMENTS: Two ways to get the time, and both are giving main character energy ✨

Open a connection to this server, and it sends you the date and time as a 32-bit number, then closes the connection.
Or send a user datagram, and it sends back a datagram containing the date and time as a 32-bit number.

No known problems 🎉 The specification should be reissued as an RFC, so that's the next glow-up 🦋

OTHER REFERENCES: (nothing listed) DEPENDENCIES: Transmission Control Protocol or User Datagram Protocol CONTACT: Postel@USC-ISIF 🍓

DCNET Time Server Protocol (Internet Clock Service) 🕰️

STATUS: Elective SPECIFICATION: RFC 778 COMMENTS: (nothing listed) OTHER REFERENCES: (nothing listed) DEPENDENCIES: Internet Control Message Protocol CONTACT: Mills@LINKABIT-DCN6 🌸

SUPDUP Protocol 🧸

STATUS: Elective SPECIFICATION: RFC 734 (in APH) COMMENTS: (nothing listed) OTHER REFERENCES: (nothing listed) DEPENDENCIES: Transmission Control Protocol CONTACT: Admin.MRC@SU-SCORE 💅

Internet Message Protocol (MPM) 📬

STATUS: Experimental SPECIFICATION: RFC 753 COMMENTS: This is an experimental multimedia mail transfer protocol 🎞️ The implementation is called a Message Processing Module, or MPM. Cute name, no cap 🥰

Please discuss any plans for implementation or use of this protocol with the contact. 🫶

OTHER REFERENCES: RFC 767 - Structured Document Formats DEPENDENCIES: Transmission Control Protocol CONTACT: Postel@USC-ISIF 💖

Appendices 🎀

Assigned Numbers 🔢

STATUS: None SPECIFICATION: RFC 820 COMMENTS: This one describes the fields of various protocols that are assigned specific values for actual use, and it lists the currently assigned values. Very organized, very iconic 📋

Issued January 1983, replaces RFC 790 in IPTW ⏳

OTHER REFERENCES: (nothing listed) CONTACT: Postel@USC-ISIF 👑

Pre-emption ⚡

STATUS: Elective SPECIFICATION: RFC 794 (in IPTW) COMMENTS: Describes how to do pre-emption of TCP connections. It's all about who gets to cut in line 🚦 OTHER REFERENCES: (nothing listed) CONTACT: Postel@USC-ISIF 💜

Service Mappings 🗺️

STATUS: None SPECIFICATION: RFC 795 (in IPTW) COMMENTS: This one describes the mapping of the IP type of service field onto the parameters of some specific networks. Mapping, but make it fashion 🧚

Out of date, needs revision 🥺

OTHER REFERENCES: (nothing listed) CONTACT: Postel@USC-ISIF 🌈

Address Mappings 🏠

STATUS: None SPECIFICATION: RFC 796 (in IPTW) COMMENTS: This one describes the mapping of the IP address field onto the address field of some specific networks. Same vibe as the last one, so yes, it's also out of date and needs revision 💀🫶

OTHER REFERENCES: (nothing listed) CONTACT: Postel@USC-ISIF 🦋

📦 where this page comes from

ietf: rfc840 1983-04
💖 girlified by claude-haiku-5-5 on 2026-10-18: a language model's rewrite of the original, under its terms