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Network Working Group                                          M. Horton
Request for Comments:  1036                       AT&T Bell Laboratories
Obsoletes: RFC-850                                              R. Adams
                                              Center for Seismic Studies
                                                           December 1987


              Standard for Interchange of USENET Messages



STATUS OF THIS MEMO

    This document defines the standard format for the interchange of
    network News messages among USENET hosts.  It updates and replaces
    RFC-850, reflecting version B2.11 of the News program.  This memo is
    disributed as an RFC to make this information easily accessible to
    the Internet community.  It does not specify an Internet standard.
    Distribution of this memo is unlimited.

1.  Introduction

    This document defines the standard format for the interchange of
    network News messages among USENET hosts.  It describes the format
    for messages themselves and gives partial standards for transmission
    of news.  The news transmission is not entirely in order to give a
    good deal of flexibility to the hosts to choose transmission
    hardware and software, to batch news, and so on.

    There are five sections to this document.  Section two defines the
    format.  Section three defines the valid control messages.  Section
    four specifies some valid transmission methods.  Section five
    describes the overall news propagation algorithm.

2.  Message Format

    The primary consideration in choosing a message format is that it
    fit in with existing tools as well as possible.  Existing tools
    include implementations of both mail and news.  (The notesfiles
    system from the University of Illinois is considered a news
    implementation.)  A standard format for mail messages has existed
    for many years on the Internet, and this format meets most of the
    needs of USENET.  Since the Internet format is extensible,
    extensions to meet the additional needs of USENET are easily made
    within the Internet standard.  Therefore, the rule is adopted that
    all USENET news messages must be formatted as valid Internet mail
    messages, according to the Internet standard RFC-822.  The USENET
    News standard is more restrictive than the Internet standard,



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    placing additional requirements on each message and forbidding use
    of certain Internet features.  However, it should always be possible
    to use a tool expecting an Internet message to process a news
    message.  In any situation where this standard conflicts with the
    Internet standard, RFC-822 should be considered correct and this
    standard in error.

    Here is an example USENET message to illustrate the fields.

              From: [e-mail] (Jerry Schwarz)
              Path: cbosgd!mhuxj!mhuxt!eagle!jerry
              Newsgroups: news.announce
              Subject: Usenet Etiquette -- Please Read
              Message-ID: <[e-mail]>
              Date: Fri, 19 Nov 82 16:14:55 GMT
              Followup-To: news.misc
              Expires: Sat, 1 Jan 83 00:00:00 -0500
              Organization: AT&T Bell Laboratories, Murray Hill

              The body of the message comes here, after a blank line.

      Here is an example of a message in the old format (before the
      existence of this standard). It is recommended that
      implementations also accept messages in this format to ease upward
      conversion.

               From: cbosgd!mhuxj!mhuxt!eagle!jerry (Jerry Schwarz)
               Newsgroups: news.misc
               Title: Usenet Etiquette -- Please Read
               Article-I.D.: eagle.642
               Posted: Fri Nov 19 16:14:55 1982
               Received: Fri Nov 19 16:59:30 1982
               Expires: Mon Jan 1 00:00:00 1990

               The body of the message comes here, after a blank line.

      Some news systems transmit news in the A format, which looks like
      this:

                Aeagle.642
                news.misc
                cbosgd!mhuxj!mhuxt!eagle!jerry
                Fri Nov 19 16:14:55 1982
                Usenet Etiquette - Please Read
                The body of the message comes here, with no blank line.

    A standard USENET message consists of several header lines, followed
    by a blank line, followed by the body of the message.  Each header



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    line consist of a keyword, a colon, a blank, and some additional
    information.  This is a subset of the Internet standard, simplified
    to allow simpler software to handle it.  The "From" line may
    optionally include a full name, in the format above, or use the
    Internet angle bracket syntax.  To keep the implementations simple,
    other formats (for example, with part of the machine address after
    the close parenthesis) are not allowed.  The Internet convention of
    continuation header lines (beginning with a blank or tab) is
    allowed.

    Certain headers are required, and certain other headers are
    optional.  Any unrecognized headers are allowed, and will be passed
    through unchanged.  The required header lines are "From", "Date",
    "Newsgroups", "Subject", "Message-ID", and "Path".  The optional
    header lines are "Followup-To", "Expires", "Reply-To", "Sender",
    "References", "Control", "Distribution", "Keywords", "Summary",
    "Approved", "Lines", "Xref", and "Organization".  Each of these
    header lines will be described below.

2.1.  Required Header lines

2.1.1.  From

    The "From" line contains the electronic mailing address of the
    person who sent the message, in the Internet syntax.  It may
    optionally also contain the full name of the person, in parentheses,
    after the electronic address.  The electronic address is the same as
    the entity responsible for originating the message, unless the
    "Sender" header is present, in which case the "From" header might
    not be verified.  Note that in all host and domain names, upper and
    lower case are considered the same, thus "[e-mail]",
    "[e-mail]", and "[e-mail]" are all equivalent.
    User names may or may not be case sensitive, for example,
    "[e-mail]" might be different from
    "[e-mail]".  Programs should avoid changing the case of
    electronic addresses when forwarding news or mail.

    RFC-822 specifies that all text in parentheses is to be interpreted
    as a comment.  It is common in Internet mail to place the full name
    of the user in a comment at the end of the "From" line.  This
    standard specifies a more rigid syntax.  The full name is not
    considered a comment, but an optional part of the header line.
    Either the full name is omitted, or it appears in parentheses after
    the electronic address of the person posting the message, or it
    appears before an electronic address which is enclosed in angle
    brackets.  Thus, the three permissible forms are:





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              From: [e-mail]
              From: [e-mail] (Mark Horton)
              From: Mark Horton <[e-mail]>

    Full names may contain any printing ASCII characters from space
    through tilde, except that they may not contain "(" (left
    parenthesis), ")" (right parenthesis), "<" (left angle bracket), or
    ">" (right angle bracket).  Additional restrictions may be placed on
    full names by the mail standard, in particular, the characters ","
    (comma), ":" (colon), "@" (at), "!" (bang), "/" (slash), "="
    (equal), and ";" (semicolon) are inadvisable in full names.

2.1.2.  Date

    The "Date" line (formerly "Posted") is the date that the message was
    originally posted to the network.  Its format must be acceptable
    both in RFC-822 and to the getdate(3) routine that is provided with
    the Usenet software.  This date remains unchanged as the message is
    propagated throughout the network.  One format that is acceptable to
    both is:

                      Wdy, DD Mon YY HH:MM:SS TIMEZONE

    Several examples of valid dates appear in the sample message above.
    Note in particular that ctime(3) format:

                          Wdy Mon DD HH:MM:SS YYYY

    is not acceptable because it is not a valid RFC-822 date.  However,
    since older software still generates this format, news
    implementations are encouraged to accept this format and translate
    it into an acceptable format.

    There is no hope of having a complete list of timezones.  Universal
    Time (GMT), the North American timezones (PST, PDT, MST, MDT, CST,
    CDT, EST, EDT) and the +/-hhmm offset specifed in RFC-822 should be
    supported.  It is recommended that times in message headers be
    transmitted in GMT and displayed in the local time zone.

2.1.3.  Newsgroups

    The "Newsgroups" line specifies the newsgroup or newsgroups in which
    the message belongs.  Multiple newsgroups may be specified,
    separated by a comma.  Newsgroups specified must all be the names of
    existing newsgroups, as no new newsgroups will be created by simply
    posting to them.





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    Wildcards (e.g., the word "all") are never allowed in a "News-
    groups" line.  For example, a newsgroup comp.all is illegal,
    although a newsgroup rec.sport.football is permitted.

    If a message is received with a "Newsgroups" line listing some valid
    newsgroups and some invalid newsgroups, a host should not remove
    invalid newsgroups from the list.  Instead, the invalid newsgroups
    should be ignored.  For example, suppose host A subscribes to the
    classes btl.all and comp.all, and exchanges news messages with host
    B, which subscribes to comp.all but not btl.all.  Suppose A receives
    a message with Newsgroups: comp.unix,btl.general.

    This message is passed on to B because B receives comp.unix, but B
    does not receive btl.general.  A must leave the "Newsgroups" line
    unchanged.  If it were to remove btl.general, the edited header
    could eventually re-enter the btl.all class, resulting in a message
    that is not shown to users subscribing to btl.general.  Also,
    follow-ups from outside btl.all would not be shown to such users.

2.1.4.  Subject

    The "Subject" line (formerly "Title") tells what the message is
    about.  It should be suggestive enough of the contents of the
    message to enable a reader to make a decision whether to read the
    message based on the subject alone.  If the message is submitted in
    response to another message (e.g., is a follow-up) the default
    subject should begin with the four characters "Re:", and the
    "References" line is required.  For follow-ups, the use of the
    "Summary" line is encouraged.

2.1.5.  Message-ID

    The "Message-ID" line gives the message a unique identifier.  The
    Message-ID may not be reused during the lifetime of any previous
    message with the same Message-ID.  (It is recommended that no
    Message-ID be reused for at least two years.)  Message-ID's have the
    syntax:

                     <string not containing blank or ">">

    In order to conform to RFC-822, the Message-ID must have the format:

                          <unique@full_domain_name>

    where full_domain_name is the full name of the host at which the
    message entered the network, including a domain that host is in, and
    unique is any string of printing ASCII characters, not including "<"
    (left angle bracket), ">" (right angle bracket), or "@" (at sign).



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    For example, the unique part could be an integer representing a
    sequence number for messages submitted to the network, or a short
    string derived from the date and time the message was created.  For
    example, a valid Message-ID for a message submitted from host ucbvax
    in domain "Berkeley.EDU" would be "<[e-mail]>".
    Programmers are urged not to make assumptions about the content of
    Message-ID fields from other hosts, but to treat them as unknown
    character strings.  It is not safe, for example, to assume that a
    Message-ID will be under 14 characters, that it is unique in the
    first 14 characters, nor that is does not contain a "/".

    The angle brackets are considered part of the Message-ID.  Thus, in
    references to the Message-ID, such as the ihave/sendme and cancel
    control messages, the angle brackets are included.  White space
    characters (e.g., blank and tab) are not allowed in a Message-ID.
    Slashes ("/") are strongly discouraged.  All characters between the
    angle brackets must be printing ASCII characters.

2.1.6.  Path

    This line shows the path the message took to reach the current
    system.  When a system forwards the message, it should add its own
    name to the list of systems in the "Path" line.  The names may be
    separated by any punctuation character or characters (except "."
    which is considered part of the hostname).  Thus, the following are
    valid entries:

                   cbosgd!mhuxj!mhuxt
                   cbosgd, mhuxj, mhuxt
                   @cbosgd.ATT.COM,@mhuxj.ATT.COM,@mhuxt.ATT.COM
                   teklabs, zehntel, sri-unix@cca!decvax

    (The latter path indicates a message that passed through decvax,
    cca, sri-unix, zehntel, and teklabs, in that order.) Additional
    names should be added from the left.  For example, the most recently
    added name in the fourth example was teklabs.  Letters, digits,
    periods and hyphens are considered part of host names; other
    punctuation, including blanks, are considered separators.

    Normally, the rightmost name will be the name of the originating
    system.  However, it is also permissible to include an extra entry
    on the right, which is the name of the sender.  This is for upward
    compatibility with older systems.

    The "Path" line is not used for replies, and should not be taken as
    a mailing address.  It is intended to show the route the message
    traveled to reach the local host.  There are several uses for this
    information.  One is to monitor USENET routing for performance



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    reasons.  Another is to establish a path to reach new hosts.
    Perhaps the most important use is to cut down on redundant USENET
    traffic by failing to forward a message to a host that is known to
    have already received it.  In particular, when host A sends a
    message to host B, the "Path" line includes A, so that host B will
    not immediately send the message back to host A.  The name each host
    uses to identify itself should be the same as the name by which its
    neighbors know it, in order to make this optimization possible.

    A host adds its own name to the front of a path when it receives a
    message from another host.  Thus, if a message with path "A!X!Y!Z"
    is passed from host A to host B, B will add its own name to the path
    when it receives the message from A, e.g., "B!A!X!Y!Z".  If B then
    passes the message on to C, the message sent to C will contain the
    path "B!A!X!Y!Z", and when C receives it, C will change it to
    "C!B!A!X!Y!Z".

    Special upward compatibility note:  Since the "From", "Sender", and
    "Reply-To" lines are in Internet format, and since many USENET hosts
    do not yet have mailers capable of understanding Internet format, it
    would break the reply capability to completely sever the connection
    between the "Path" header and the reply function.  It is recognized
    that the path is not always a valid reply string in older
    implementations, and no requirement to fix this problem is placed on
    implementations.  However, the existing convention of placing the
    host name and an "!"  at the front of the path, and of starting the
    path with the host name, an "!", and the user name, should be
    maintained when possible.

2.2.  Optional Headers

2.2.1.  Reply-To

    This line has the same format as "From".  If present, mailed replies
    to the author should be sent to the name given here.  Otherwise,
    replies are mailed to the name on the "From" line. (This does not
    prevent additional copies from being sent to recipients named by the
    replier, or on "To" or "Cc" lines.)  The full name may be optionally
    given, in parentheses, as in the "From" line.

2.2.2.  Sender

    This field is present only if the submitter manually enters a "From"
    line.  It is intended to record the entity responsible for
    submitting the message to the network.  It should be verified by the
    software at the submitting host.





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    For example, if John Smith is visiting CCA and wishes to post a
    message to the network, using friend Sarah Jones' account, the
    message might read:

              From: [e-mail] (John Smith)
              Sender: [e-mail] (Sarah Jones)

    If a gateway program enters a mail message into the network at host
    unix.SRI.COM, the lines might read:

              From: [e-mail]
              Sender: [e-mail]

    The primary purpose of this field is to be able to track down
    messages to determine how they were entered into the network.  The
    full name may be optionally given, in parentheses, as in the "From"
    line.

2.2.3.  Followup-To

    This line has the same format as "Newsgroups".  If present, follow-
    up messages are to be posted to the newsgroup or newsgroups listed
    here.  If this line is not present, follow-ups are posted to the
    newsgroup or newsgroups listed in the "Newsgroups" line.

    If the keyword poster is present, follow-up messages are not
    permitted.  The message should be mailed to the submitter of the
    message via mail.

2.2.4.  Expires

    This line, if present, is in a legal USENET date format.  It
    specifies a suggested expiration date for the message.  If not
    present, the local default expiration date is used.  This field is
    intended to be used to clean up messages with a limited usefulness,
    or to keep important messages around for longer than usual.  For
    example, a message announcing an upcoming seminar could have an
    expiration date the day after the seminar, since the message is not
    useful after the seminar is over.  Since local hosts have local
    policies for expiration of news (depending on available disk space,
    for instance), users are discouraged from providing expiration dates
    for messages unless there is a natural expiration date associated
    with the topic.  System software should almost never provide a
    default "Expires" line.  Leave it out and allow local policies to be
    used unless there is a good reason not to.






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2.2.5.  References

    This field lists the Message-ID's of any messages prompting the
    submission of this message.  It is required for all follow-up
    messages, and forbidden when a new subject is raised.
    Implementations should provide a follow-up command, which allows a
    user to post a follow-up message.  This command should generate a
    "Subject" line which is the same as the original message, except
    that if the original subject does not begin with "Re:" or "re:", the
    four characters "Re:" are inserted before the subject.  If there is
    no "References" line on the original header, the "References" line
    should contain the Message-ID of the original message (including the
    angle brackets).  If the original message does have a "References"
    line, the follow-up message should have a "References" line
    containing the text of the original "References" line, a blank, and
    the Message-ID of the original message.

    The purpose of the "References" header is to allow messages to be
    grouped into conversations by the user interface program.  This
    allows conversations within a newsgroup to be kept together, and
    potentially users might shut off entire conversations without
    unsubscribing to a newsgroup.  User interfaces need not make use of
    this header, but all automatically generated follow-ups should
    generate the "References" line for the benefit of systems that do
    use it, and manually generated follow-ups (e.g., typed in well after
    the original message has been printed by the machine) should be
    encouraged to include them as well.

    It is permissible to not include the entire previous "References"
    line if it is too long.  An attempt should be made to include a
    reasonable number of backwards references.

2.2.6.  Control

    If a message contains a "Control" line, the message is a control
    message.  Control messages are used for communication among USENET
    host machines, not to be read by users.  Control messages are
    distributed by the same newsgroup mechanism as ordinary messages.
    The body of the "Control" header line is the message to the host.

    For upward compatibility, messages that match the newsgroup pattern
    "all.all.ctl" should also be interpreted as control messages.  If no
    "Control" header is present on such messages, the subject is used as
    the control message.  However, messages on newsgroups matching this
    pattern do not conform to this standard.






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    Also for upward compatibility, if the first 4 characters of the
    "Subject:" line are "cmsg", the rest of the "Subject:" line should
    be interpreted as a control message.

2.2.7.  Distribution

    This line is used to alter the distribution scope of the message.
    It is a comma separated list similar to the "Newsgroups" line.  User
    subscriptions are still controlled by "Newsgroups", but the message
    is sent to all systems subscribing to the newsgroups on the
    "Distribution" line in addition to the "Newsgroups" line.  For the
    message to be transmitted, the receiving site must normally receive
    one of the specified newsgroups AND must receive one of the
    specified distributions.  Thus, a message concerning a car for sale
    in New Jersey might have headers including:

                   Newsgroups: rec.auto,misc.forsale
                   Distribution: nj,ny

    so that it would only go to persons subscribing to rec.auto or misc.
    for sale within New Jersey or New York.  The intent of this header
    is to restrict the distribution of a newsgroup further, not to
    increase it.  A local newsgroup, such as nj.crazy-eddie, will
    probably not be propagated by hosts outside New Jersey that do not
    show such a newsgroup as valid.  A follow-up message should default
    to the same "Distribution" line as the original message, but the
    user can change it to a more limited one, or escalate the
    distribution if it was originally restricted and a more widely
    distributed reply is appropriate.

2.2.8.  Organization

    The text of this line is a short phrase describing the organization
    to which the sender belongs, or to which the machine belongs.  The
    intent of this line is to help identify the person posting the
    message, since host names are often cryptic enough to make it hard
    to recognize the organization by the electronic address.

2.2.9.  Keywords

    A few well-selected keywords identifying the message should be on
    this line.  This is used as an aid in determining if this message is
    interesting to the reader.

2.2.10.  Summary

    This line should contain a brief summary of the message.  It is
    usually used as part of a follow-up to another message.  Again, it



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    is very useful to the reader in determining whether to read the
    message.

2.2.11.  Approved

    This line is required for any message posted to a moderated
    newsgroup.  It should be added by the moderator and consist of his
    mail address.  It is also required with certain control messages.

2.2.12.  Lines

    This contains a count of the number of lines in the body of the
    message.

2.2.13.  Xref

    This line contains the name of the host (with domains omitted) and a
    white space separated list of colon-separated pairs of newsgroup
    names and message numbers.  These are the newsgroups listed in the
    "Newsgroups" line and the corresponding message numbers from the
    spool directory.

    This is only of value to the local system, so it should not be
    transmitted.  For example, in:

               Path: seismo!lll-crg!lll-lcc!pyramid!decwrl!reid
               From: [e-mail] (Brian Reid)
               Newsgroups: news.lists,news.groups
               Subject: USENET READERSHIP SUMMARY REPORT FOR SEP 86
               Message-ID: <[e-mail]>
               Date: 1 Oct 86 11:26:15 GMT
               Organization: DEC Western Research Laboratory
               Lines: 441
               Approved: [e-mail]
               Xref: seismo news.lists:461 news.groups:6378

    the "Xref" line shows that the message is message number 461 in the
    newsgroup news.lists, and message number 6378 in the newsgroup
    news.groups, on host seismo.  This information may be used by
    certain user interfaces.

3.  Control Messages

    This section lists the control messages currently defined.  The body
    of the "Control" header line is the control message.  Messages are a
    sequence of zero or more words, separated by white space (blanks or
    tabs).  The first word is the name of the control message, remaining
    words are parameters to the message.  The remainder of the header



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    and the body of the message are also potential parameters; for
    example, the "From" line might suggest an address to which a
    response is to be mailed.

    Implementors and administrators may choose to allow control messages
    to be carried out automatically, or to queue them for annual
    processing.  However, manually processed messages should be dealt
    with promptly.

    Failed control messages should NOT be mailed to the originator of
    the message, but to the local "usenet" account.

3.1.  Cancel

                     cancel <Message-ID>


    If a message with the given Message-ID is present on the local
    system, the message is cancelled.  This mechanism allows a user to
    cancel a message after the message has been distributed over the
    network.

    If the system is unable to cancel the message as requested, it
    should not forward the cancellation request to its neighbor systems.

    Only the author of the message or the local news administrator is
    allowed to send this message.  The verified sender of a message is
    the "Sender" line, or if no "Sender" line is present, the "From"
    line.  The verified sender of the cancel message must be the same as
    either the "Sender" or "From" field of the original message.  A
    verified sender in the cancel message is allowed to match an
    unverified "From" in the original message.

3.2.  Ihave/Sendme

                   ihave <Message-ID list> [<remotesys>]
                   sendme <Message-ID list> [<remotesys>]

    This message is part of the ihave/sendme protocol, which allows one
    host (say A) to tell another host (B) that a particular message has
    been received on A.  Suppose that host A receives message
    "<[e-mail]>", and wishes to transmit the message to
    host B.

    A sends the control message "ihave <[e-mail]> A" to
    host B (by posting it to newsgroup to.B).  B responds with the
    control message "sendme <[e-mail]> B" (on newsgroup
    to.A), if it has not already received the message.  Upon receiving



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    the sendme message, A sends the message to B.

    This protocol can be used to cut down on redundant traffic between
    hosts.  It is optional and should be used only if the particular
    situation makes it worthwhile.  Frequently, the outcome is that,
    since most original messages are short, and since there is a high
    overhead to start sending a new message with UUCP, it costs as much
    to send the ihave as it would cost to send the message itself.

    One possible solution to this overhead problem is to batch requests.
    Several Message-ID's may be announced or requested in one message.
    If no Message-ID's are listed in the control message, the body of
    the message should be scanned for Message-ID's, one per line.

3.3.  Newgroup

                      newgroup <groupname> [moderated]

    This control message creates a new newsgroup with the given name.
    Since no messages may be posted or forwarded until a newsgroup is
    created, this message is required before a newsgroup can be used.
    The body of the message is expected to be a short paragraph
    describing the intended use of the newsgroup.

    If the second argument is present and it is the keyword moderated,
    the group should be created moderated instead of the default of
    unmoderated.  The newgroup message should be ignored unless there is
    an "Approved" line in the same message header.

3.4.  Rmgroup

                            rmgroup <groupname>

    This message removes a newsgroup with the given name.  Since the
    newsgroup is removed from every host on the network, this command
    should be used carefully by a responsible administrator.  The
    rmgroup message should be ignored unless there is an "Approved:"
    line in the same message header.













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3.5.  Sendsys
                           sendsys (no arguments)

    The sys file, listing all neighbors and the newsgroups to be sent to
    each neighbor, will be mailed to the author of the control message
    ("Reply-To", if present, otherwise "From").  This information is
    considered public information, and it is a requirement of membership
    in USENET that this information be provided on request, either
    automatically in response to this control message, or manually, by
    mailing the requested information to the author of the message.
    This information is used to keep the map of USENET up to date, and
    to determine where netnews is sent.

    The format of the file mailed back to the author should be the same
    as that of the sys file.  This format has one line per neighboring
    host (plus one line for the local host), containing four colon
    separated fields.  The first field has the host name of the
    neighbor, the second field has a newsgroup pattern describing the
    newsgroups sent to the neighbor.  The third and fourth fields are
    not defined by this standard.  The sys file is not the same as the
    UUCP L.sys file.  A sample response is:

      From: cbosgd!mark  (Mark Horton)
      Date: Sun, 27 Mar 83 20:39:37 -0500
      Subject: response to your sendsys request
      To: [e-mail]

      Responding-System: cbosgd.ATT.COM
      cbosgd:osg,cb,btl,bell,world,comp,sci,rec,talk,misc,news,soc,to,
            test
      ucbvax:world,comp,to.ucbvax:L:
      cbosg:world,comp,bell,btl,cb,osg,to.cbosg:F:/usr/spool/outnews
            /cbosg
      cbosgb:osg,to.cbosgb:F:/usr/spool/outnews/cbosgb
      sescent:world,comp,bell,btl,cb,to.sescent:F:/usr/spool/outnews
            /sescent
      npois:world,comp,bell,btl,ug,to.npois:F:/usr/spool/outnews/npois
      mhuxi:world,comp,bell,btl,ug,to.mhuxi:F:/usr/spool/outnews/mhuxi

3.6.  Version

                           version (no arguments)

    The name and version of the software running on the local system is
    to be mailed back to the author of the message ("Reply-to" if
    present, otherwise "From").

3.7.  Checkgroups



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RFC 1036              Standard for USENET Messages         December 1987


    The message body is a list of "official" newsgroups and their
    description, one group per line.  They are compared against the list
    of active newsgroups on the current host.  The names of any obsolete
    or new newsgroups are mailed to the user "usenet" and descriptions
    of the new newsgroups are added to the help file used when posting
    news.

4.  Transmission Methods

    USENET is not a physical network, but rather a logical network
    resting on top of several existing physical networks.  These
    networks include, but are not limited to, UUCP, the Internet, an
    Ethernet, the BLICN network, an NSC Hyperchannel, and a BERKNET.
    What is important is that two neighboring systems on USENET have
    some method to get a new message, in the format listed here, from
    one system to the other, and once on the receiving system, processed
    by the netnews software on that system.  (On UNIX systems, this
    usually means the rnews program being run with the message on the
    standard input. <1>)

    It is not a requirement that USENET hosts have mail systems capable
    of understanding the Internet mail syntax, but it is strongly
    recommended.  Since "From", "Reply-To", and "Sender" lines use the
    Internet syntax, replies will be difficult or impossible without an
    Internet mailer.  A host without an Internet mailer can attempt to
    use the "Path" header line for replies, but this field is not
    guaranteed to be a working path for replies.  In any event, any host
    generating or forwarding news messages must have an Internet address
    that allows them to receive mail from hosts with Internet mailers,
    and they must include their Internet address on their From line.

4.1.  Remote Execution

    Some networks permit direct remote command execution.  On these
    networks, news may be forwarded by spooling the rnews command with
    the message on the standard input.  For example, if the remote
    system is called remote, news would be sent over a UUCP link
    with the command:

                              uux - remote!rnews

    and on a Berknet:

                              net -mremote rnews







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RFC 1036              Standard for USENET Messages         December 1987


    It is important that the message be sent via a reliable mechanism,
    normally involving the possibility of spooling, rather than direct
    real-time remote execution.  This is because, if the remote system
    is down, a direct execution command will fail, and the message will
    never be delivered.  If the message is spooled, it will eventually
    be delivered when both systems are up.

4.2.  Transfer by Mail

    On some systems, direct remote spooled execution is not possible.
    However, most systems support electronic mail, and a news message
    can be sent as mail.  One approach is to send a mail message which
    is identical to the news message: the mail headers are the news
    headers, and the mail body is the news body.  By convention, this
    mail is sent to the user newsmail on the remote machine.

    One problem with this method is that it may not be possible to
    convince the mail system that the "From" line of the message is
    valid, since the mail message was generated by a program on a
    system different from the source of the news message.  Another
    problem is that error messages caused by the mail transmission
    would be sent to the originator of the news message, who has no
    control over news transmission between two cooperating hosts
    and does not know whom to contact.  Transmission error messages
    should be directed to a responsible contact person on the
    sending machine.

    A solution to this problem is to encapsulate the news message into a
    mail message, such that the entire message (headers and body) are
    part of the body of the mail message.  The convention here is that
    such mail is sent to user rnews on the remote system.  A mail
    message body is generated by prepending the letter N to each line of
    the news message, and then attaching whatever mail headers are
    convenient to generate.  The N's are attached to prevent any special
    lines in the news message from interfering with mail transmission,
    and to prevent any extra lines inserted by the mailer (headers,
    blank lines, etc.) from becoming part of the news message.  A
    program on the receiving machine receives mail to rnews, extracting
    the message itself and invoking the rnews program.  An example in
    this format might look like this:











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RFC 1036              Standard for USENET Messages         December 1987


                Date: Mon, 3 Jan 83 08:33:47 MST
                From: [e-mail]
                Subject: network news message
                To: [e-mail]

                NPath: cbosgd!mhuxj!harpo!utah-cs!sask!derek
                NFrom: [e-mail] (Derek Andrew)
                NNewsgroups: misc.test
                NSubject: necessary test
                NMessage-ID: <[e-mail]>
                NDate: Mon, 3 Jan 83 00:59:15 MST
                N
                NThis really is a test.  If anyone out there more than 6
                Nhops away would kindly confirm this note I would
                Nappreciate it.  We suspect that our news postings
                Nare not getting out into the world.
                N

    Using mail solves the spooling problem, since mail must always be
    spooled if the destination host is down.  However, it adds more
    overhead to the transmission process (to encapsulate and extract the
    message) and makes it harder for software to give different
    priorities to news and mail.

4.3.  Batching

    Since news messages are usually short, and since a large number of
    messages are often sent between two hosts in a day, it may make
    sense to batch news messages.  Several messages can be combined into
    one large message, using conventions agreed upon in advance by the
    two hosts.  One such batching scheme is described here; its use is
    highly recommended.

    News messages are combined into a script, separated by a header of
    the form:


                   #! rnews 1234

    where 1234 is the length of the message in bytes.  Each such line is
    followed by a message containing the given number of bytes.  (The
    newline at the end of each line of the message is counted as one
    byte, for purposes of this count, even if it is stored as <CARRIAGE
    RETURN><LINE FEED>.)  For example, a batch of message might look
    like this:






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RFC 1036              Standard for USENET Messages         December 1987


                #! rnews 239
                From: [e-mail] (Jerry Schwarz)
                Path: cbosgd!mhuxj!mhuxt!eagle!jerry
                Newsgroups: news.announce
                Subject: Usenet Etiquette -- Please Read
                Message-ID: <[e-mail]>
                Date: Fri, 19 Nov 82 16:14:55 EST
                Approved: [e-mail]

                Here is an important message about USENET Etiquette.
                #! rnews 234
                From: [e-mail] (Jerry Schwarz)
                Path: cbosgd!mhuxj!mhuxt!eagle!jerry
                Newsgroups: news.announce
                Subject: Notes on Etiquette message
                Message-ID: <[e-mail]>
                Date: Fri, 19 Nov 82 17:24:12 EST
                Approved: [e-mail]

                There was something I forgot to mention in the last
                message.

    Batched news is recognized because the first character in the
    message is #.  The message is then passed to the unbatcher for
    interpretation.

    The second argument (in this example rnews) determines which
    batching scheme is being used.  Cooperating hosts may use whatever
    scheme is appropriate for them.

5.  The News Propagation Algorithm

    This section describes the overall scheme of USENET and the
    algorithm followed by hosts in propagating news to the entire
    logical network.  Since all hosts are affected by incorrectly
    formatted messages and by propagation errors, it is important
    for the method to be standardized.

    USENET is a directed graph.  Each node in the graph is a host
    computer, and each arc in the graph is a transmission path from
    one host to another host.  Each arc is labeled with a newsgroup
    pattern, specifying which newsgroup classes are forwarded along
    that link.  Most arcs are bidirectional, that is, if host A
    sends a class of newsgroups to host B, then host B usually sends
    the same class of newsgroups to host A.  This bidirectionality
    is not, however, required.

    USENET is made up of many subnetworks.  Each subnet has a name, such



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RFC 1036              Standard for USENET Messages         December 1987


    as comp or btl.  Each subnet is a connected graph, that is, a path
    exists from every node to every other node in the subnet.  In
    addition, the entire graph is (theoretically) connected.  (In
    practice, some political considerations have caused some hosts to be
    unable to post messages reaching the rest of the network.)

    A message is posted on one machine to a list of newsgroups. That
    machine accepts it locally, then forwards it to all its neighbors
    that are interested in at least one of the newsgroups of the
    message.  (Site A deems host B to be "interested" in a newsgroup if
    the newsgroup matches the pattern on the arc from A to B.  This
    pattern is stored in a file on the A machine.)  The hosts receiving
    the incoming message examine it to make sure they really want the
    message, accept it locally, and then in turn forward the message to
    all their interested neighbors.  This process continues until the
    entire network has seen the message.

    An important part of the algorithm is the prevention of loops.  The
    above process would cause a message to loop along a cycle forever.
    In particular, when host A sends a message to host B, host B will
    send it back to host A, which will send it to host B, and so on.
    One solution to this is the history mechanism.  Each host keeps
    track of all messages it has seen (by their Message-ID) and
    whenever a message comes in that it has already seen, the incoming
    message is discarded immediately.  This solution is sufficient to
    prevent loops, but additional optimizations can be made to avoid
    sending messages to hosts that will simply throw them away.

    One optimization is that a message should never be sent to a machine
    listed in the "Path" line of the header.  When a machine name is
    in the "Path" line, the message is known to have passed through the
    machine.  Another optimization is that, if the message originated
    on host A, then host A has already seen the message.  Thus, if a
    message is posted to newsgroup misc.misc, it will match the pattern
    misc.all (where all is a metasymbol that matches any string), and
    will be forwarded to all hosts that subscribe to misc.all (as
    determined by what their neighbors send them).  These hosts make up
    the misc subnetwork.  A message posted to btl.general will reach all
    hosts receiving btl.all, but will not reach hosts that do not get
    btl.all.  In effect, the messages reaches the btl subnetwork.  A
    messages posted to newsgroups misc.misc,btl.general will reach all
    hosts subscribing to either of the two classes.

Notes

    <1>  UNIX is a registered trademark of AT&T.





Horton & Adams                                                 [Page 19]