RFC 850 June 1983 Standard for Interchange of USENET Messages Mark R. Horton [ This memo is distributed as an RFC   only  to  make  this information  easily  accessible to researchers in the ARPA community.  It does not specify  an  Internet  standard. ]  1.  Introduction This document defines the standard format for  interchange of Network News articles among USENET sites.  It describes the format for  articles  themselves,  and  gives  partial standards for transmission of news.  The news transmission is not entirely standardized in order to give a good  deal of   flexibility   to   the  individual  hosts  to  choose transmission hardware and software, whether to batch news, and so on. There are five sections to  this  document.   Section  two section  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.  Article Format The primary consideration in choosing an article format is that  it  fit  in with existing tools as well as possible. Existing tools include both implementations  of  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 ARPANET, and this  format  meets  most  of  the  needs  of USENET.    Since   the   ARPANET   format  is  extensible, extensions to meet the  additional  needs  of  USENET  are easily  made  within the ARPANET standard.  Therefore, the rule is adopted that all  USENET  news  articles  must  be formatted as valid ARPANET mail messages, according to the ARPANET  standard RFC  822 .    This   standard   is   more restrictive  than the ARPANET standard, placing additional requirements on each article and forbidding use of certain ARPANET  features.   However, it should always be possible to use a tool expecting an ARPANET message  to  process  a news  article.   In  any  situation  where  this  standard conflicts with the ARPANET standard, RFC  822 should  be considered correct and this standard in error. - 1 - An example message is included to illustrate the fields. Relay-Version: version B 2.10 2/13/83; site cbosgd.UUCP Posting-Version: version B 2.10 2/13/83; site eagle.UUCP Path: cbosgd!mhuxj!mhuxt!eagle!jerry From:  jerry@eagle.uucp  (Jerry Schwarz) Newsgroups: net.general Subject: Usenet Etiquette -- Please Read Message-ID: < 642@eagle.UUCP > Date: Friday, 19-Nov-82 16:14:55 EST Followup-To: net.news Expires: Saturday, 1-Jan-83 00:00:00 EST Date-Received: Friday, 19-Nov-82 16:59:30 EST Organization: Bell Labs, Murray Hill The body of the article 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 articles  in  this  format  to ease upward conversion. From: cbosgd!mhuxj!mhuxt!eagle!jerry (Jerry Schwarz) Newsgroups: net.general 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 article comes here, after a blank line. Some news systems transmit news in the   "A"  format, which looks like this: Aeagle.642 net.general cbosgd!mhuxj!mhuxt!eagle!jerry Fri Nov 19 16:14:55 1982 Usenet Etiquette - Please Read The body of the article comes here, with no blank line. An article consists of several header lines, followed by a blank  line,  followed  by  the  body of the message.  The header lines consist of a keyword, a colon, a  blank,  and some  additional  information.   This  is  a subset of the ARPANET 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  ARPANET  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 ARPANET convention of continuation header lines (beginning with  a blank or tab) is allowed. - 2 - Certain  headers  are  required,   certain   headers   are optional.   Any unrecognized headers are allowed, and will be passed through unchanged.   The  required  headers  are Relay-Version,  Posting-Version,  From,  Date, Newsgroups, Subject,  Message-ID,  Path.   The  optional  headers  are Followup-To,  Date-Received,  Expires,  Reply-To,  Sender, References, Control, Distribution, Organization. 2.1  Required Headers 2.1.1   Relay-Version  This header line shows  the  version of  the  program  responsible for the transmission of this article over the immediate link, that is, the program that is  relaying the article from the next site.  For example, suppose site A sends an article to  site  B,  and  site  B forwards  the  article  to  site  C.   The  message  being transmitted from A to B would have a Relay-Version  header identifying  the  program  running  on  A, and the message transmitted from B to C would identify the program running on  B.  This header can be used to interpret older headers in an upward compatible way.  Relay-Version must always be the  first  in  a message; thus, all articles meeting this standard will begin with an upper case    "R".     No  other restrictions are placed on the order of header lines. The line contains two  fields,  separated  by  semicolons. The fields are the version and the full domain name of the site.  The version should identify the system program used (e.g.,   "B")    as  well  as  a version number and version date.  For example, the header line might contain Relay-Version: version B 2.10 2/13/83; site cbosgd.UUCP This header should not be passed on to  additional  sites. A  relay  program,  when  passing  an  article  on, should include only its own Relay-Version, not the  Relay-Version of  some other site.   (For upward compatibility with older software, if a Relay-Version is found in a header which is not the first line, it should be assumed to be moved by an older version of news and deleted.) 2.1.2   Posting-Version    This   header   identifies   the software  responsible  for  entering this message into the network.  It has the same  format  as  Relay-Version.   It will  normally  identify  the same site as the Message-ID, unless the posting site is serving  as  a  gateway  for  a message  that  already  contains a message ID generated by mail.   (While it is permissible for a gateway  to  use  an externally  generated message ID, the message ID should be checked to ensure it conforms to this standard and to  RFC 822.) - 3 - 2.1.3   From  The From line contains the electronic mailing address  of  the  person who sent the message, in the ARPA 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 article, unless the Sender header is present, in which case the From header might not be  verified.   Note  that  in  all site and domain names, upper  and  lower  case  are  considered  the  same,  thus mark@cbosgd.UUCP ,   mark@cbosgd.uucp ,  and  mark@CBosgD.UUcp are all equivalent.  User names may or  may  not  be  case sensitive,   for   example,    Billy@cbosgd.UUCP   might  be different from  BillY@cbosgd.UUCP.    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 ARPANET 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 article, or it appears before an electronic address enclosed in  angle  brackets. Thus, the three permissible forms are: From:  mark@cbosgd.UUCP From:  mark@cbosgd.UUCP  (Mark Horton) From: Mark Horton < mark@cbosgd.UUCP > Full names may contain any printing ASCII characters  from space through tilde, with the exceptions that they may not contain parentheses   "("   or   ")",   or  angle  brackets "<"   or  ">".     Additional restrictions may be placed on full names  by  the  mail  standard,  in  particular,  the characters  comma    ",",  colon  ":",  and semicolon   ";"  are inadvisable in full names. 2.1.4  Date  The Date line (formerly   "Posted")   is  the date,  in  a  format  that  must be acceptable both to the ARPANET and to the getdate routine, that the  article  was originally  posted  to  the  network.   This  date remains unchanged as the  article  is  propagated  throughout  the network.  One format that is acceptable to both is Weekday, DD-Mon-YY HH:MM:SS TIMEZONE Several examples of  valid  dates  appear  in  the  sample article above.  Note in particular that ctime format: Wdy Mon DD HH:MM:SS YYYY - 4 - is not acceptable because it is not a valid ARPANET  date. However, since older software still generates this format, news implementations are encouraged to accept this  format and translate it into an acceptable format. The contents of the TIMEZONE field is currently subject to worldwide time zone  abbreviations,  including  the  usual American  zones   (PST,  PDT, MST, MDT, CST, CDT, EST, EDT), the   other   North   American   zones    (Bering   through Newfoundland),  European  zones,  Australian zones, and so on.  Lacking a complete list at present (and unsure if  an unambiguous   list   exists),   authors  of  software  are encouraged to keep this code flexible, and  in  particular not  to  assume  that  time  zone  names are exactly three letters long.   Implementations  are  free  to  edit  this field,  keeping  the  time the same, but changing the time zone (with an appropriate adjustment   to  the  local  time shown) to a known time zone. 2.1.5   Newsgroups  The  Newsgroups  line  specifies  which newsgroup  or newsgroups the article belongs in.  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. Wildcards (e.g., the word  "all")   are never allowed in  a Newsgroups  line.  For example, a newsgroup   "net.all"  is illegal, although a newsgroup name     "net.sport.football"  is permitted. If an article is received with a Newsgroups  line  listing some  valid newsgroups and some invalid newsgroups, a site should  not  remove  invalid  newsgroups  from  the  list. Instead,  the  invalid  newsgroups should be ignored.  For example,  suppose  site  A  subscribes  to   the   classes "btl.all"   and   "net.all",    and exchanges news articles with site B,  which  subscribes  to    "net.all"   but  not "btl.all".       Suppose   A   receives   an  article  with "Newsgroups: net.micro,btl.general".      This  article  is passed  on  to  B because B receives net.micro, but B does not receive btl.general.  A must leave the Newsgroup  line unchanged.   If  it  were  to  remove   "btl.general",  the edited header could  eventually  reenter  the     "btl.all"  class,  resulting in an article that is not shown to users subscribing  to    "btl.general".     Also,  followups  from outside   "btl.all"   would not be shown to such users. - 5 - 2.1.6   Subject   The  Subject  line   (formerly    "Title") tells  what the article is about.  It should be suggestive enough of the contents of the article to enable  a  reader to  make  a  decision whether to read the article based on the  subject  alone.   If  the  article  is  submitted  in response  to another article (e.g., is a  "followup")  the default subject should  begin  with  the  four  characters "Re: "    and the References line is required.     (The user might wish to edit the subject of the  followup,  but  the default should begin with   "Re: ".) 2.1.7   Message-ID  The Message-ID line gives the article a unique  identifier.  The same message ID may not be reused during the lifetime of any article 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 article entered the network, including a domain that host is in, and unique  is  any  string  of  printing ASCII  characters,  not  including   "<", ">", or "@".  For example,  the   "unique"    part   could   be   an   integer representing  a  sequence number for articles submitted to the network, or a short string derived from the  date  and time  the article was created.  For example, valid message ID for an article submitted from  site  ucbvax  in  domain Berkeley.ARPA   would   be   "< 4123@ucbvax.Berkeley.ARPA >". 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,  nor  that  it  is  unique  in  the  first  14 characters. 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.   All characters  between  the  angle  brackets must be printing ASCII characters. 2.1.8   Path  This line shows the path the article 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,      thus - 6 - "cbosgd!mhuxj!mhuxt",    "cbosgd,  mhuxj,  mhuxt",     and "@cbosgd.uucp,@mhuxj.uucp,@mhuxt.uucp"      and       even "teklabs,   zehntel,    sri-unix@cca ! decvax"    are   valid entries.   (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 third example was   "teklabs".    Letters,  digits,  periods and  hyphens  are  considered  part  of  site 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 system. 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  travelled  to  reach  the  local  site. There  are  several  uses for this information.  One is to monitor USENET routing for performance  reasons.   Another is  to  establish  a path to reach new sites.  Perhaps the most important is to cut down on redundant USENET  traffic by failing to forward a message to a site that is known to have already received it.   In  particular,  when  site  A sends  an article to site B, the Path line includes    "A", so that site B will not immediately send the article  back to  site  A.   The  site  name  each site 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 site adds its own name to the front of a  path  when  it receives  a message from another site.  Thus, if a message with path A!X!Y!Z is passed from site A to site 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  sites  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.   Thus, sites are required to continue to keep the Path line  in  a  working reply  format  as much as possible, until January 1, 1984. 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 - 7 - existing  convention of placing the site name and an    "!"  at the front of the path, and of starting  the  path  with the  site  name,  an    "!",    and the user name, should be maintained at least until 1984. 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  article  to  the network,  and  should  be  verified by the software at the submitting site. For example, if John Smith is visiting CCA and  wishes  to post  an  article to the network, using friend Sarah Jones account, the message might read From:  smith@ucbvax.uucp  (John Smith) Sender: jones@cca.arpa (Sarah Jones) If a gateway  program  enters  a  mail  message  into  the network at site sri-unix, the lines might read From: John.Doe@CMU-CS-A.ARPA Sender: network@sri-unix.ARPA The primary purpose of this field is to be able  to  track down  articles 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  articles  are to be posted to the newsgroup(s) listed here.   If this  line  is not  present,  followups  are  posted  to the newsgroup(s) listed in the Newsgroups line, except  that  followups  to "net.general"   should instead go to   "net.followup". 2.2.4  Date-Received  This line (formerly  "Received")  is in  a  legal  USENET date format.  It records the date and time that the article was  first  received  on  the  local system.   If  this  line  is  present  in an article being transmitted from one host to another, the  receiving  host should  ignore  it  and  replace it with the current date. Since this field is intended for local use only,  no  site is  required  to support it.  However, no site should pass this field on to another site unchanged. - 8 - 2.2.5   Expires  This line,  if  present,  is  in  a  legal USENET  date  format.  It specifies a suggested expiration date for the article.  If not present, the  local  default expiration date is used. This field is intended to be used  to  clean  up  articles with  a  limited usefulness, or to keep important articles 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 sites have local  policies  for  expiration  of  news   (depending  on available disk space, for instance), users are discouraged from providing expiration dates for articles 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. 2.2.6   References  This field lists the  message  ID's  of any articles prompting the submission of this article.  It is required for all follow-up articles, and forbidden when a new subject is raised.  Implementations should provide a follow-up command, which allows a user to post a follow-up article.   This  command  should  generate  a Subject line which is the same as the original article, 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  article (including the angle brackets). If the original article does have a References  line,  the followup  article should have a References line containing the text of the original References line, a blank, and the message ID of the original article. The purpose of the References header is to allow  articles 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  may not make use of this header, but all automatically  generated  followups  should  generate  the References line for the benefit of systems that do use it, and manually generated followups (e.g. typed in well after the  original  article  has  been  printed by the machine) should be encouraged to include them as well. 2.2.7   Control  If an article contains a Control line, the article  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. - 9 - 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. 2.2.8   Distribution   This  line  is  used  to  alter  the distribution scope of the message.  It has the same format as 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 instead of the Newsgroups line.  Thus, a car for sale in New Jersey might have headers including Newsgroups: net.auto,net.wanted Distribution: nj.all so that  it  would  only  go  to  persons  subscribing  to net.auto  or  net.wanted within New Jersey.  The intent of this header is to further restrict the distribution  of  a newsgroup, not to increase it.  A local newsgroup, such as nj.crazy-eddie, will probably not be propagated  by  sites outside  New  Jersey  that do not show such a newsgroup as valid.  Wildcards in newsgroup names in  the  Distribution line are allowed.  Followup articles should default to the same Distribution line as the original  article,  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. 2.2.9   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 site names are often cryptic enough to make it  hard  to  recognize the organization by the electronic address. 3.  Control Messages This section lists the control messages currently defined. The  body  of  the  Control header 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 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. - 10 - Implementors  and  administrators  may  choose  to   allow control  messages  to  be automatically carried out, or to queue  them  for  manual  processing.   However,  manually processed messages should be dealt with promptly. 3.1  Cancel cancel <message ID> If an article with the given message ID is present on  the local  system,  the  article is cancelled.  This mechanism allows a user to cancel an article after the  article  has been distributed over the network. Only the author of the article or the local super user  is allowed  to  use  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  site   (say  "A")   to tell another site ("B")   that  a particular message has been received on  A. Suppose  that site A receives article   "ucbvax.1234",  and wishes to transmit the article to site  B.   A  sends  the control  message    "ihave  ucbvax.1234  A"   to site B (by posting it to newsgroup   "to.B").    B  responds  with  the control  message    "sendme  ucbvax.1234  B"  (on newsgroup to.A) if it has not already received  the  article.   Upon receiving the Sendme message, A sends the article to B. This protocol can be used to cut down on redundant traffic between  sites.  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 article 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. - 11 - 3.3  Newgroup newgroup <groupname> This control message creates a new newsgroup with the name given.  Since no articles 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. 3.4  Rmgroup rmgroup <groupname> This message removes a  newsgroup  with  the  given  name. Since  the  newsgroup  is  removed  from every site on the network, this  command  should  be  used  carefully  by  a responsible administrator. 3.5  Sendsys sendsys (no arguments) The    "sys"    file,  listing  all  neighbors   and   which newsgroups  are  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 site (plus one   line  for  the  local site),  containing four colon separated fields.  The first field has the site 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.  A sample response: From cbosgd!mark  Sun Mar 27 20:39:37 1983 Subject: response to your sendsys request To:  mark@cbosgd.UUCP - 12 - Responding-System: cbosgd.UUCP cbosgd:osg,cb,btl,bell,net,fa,to,test ucbvax:net,fa,to.ucbvax:L: cbosg:net,fa,bell,btl,cb,osg,to.cbosg:F:/usr/spool/outnews/cbosg cbosgb:osg,to.cbosgb:F:/usr/spool/outnews/cbosgb sescent:net,fa,bell,btl,cb,to.sescent:F:/usr/spool/outnews/sescent npois:net,fa,bell,btl,ug,to.npois:F:/usr/spool/outnews/npois mhuxi:net,fa,bell,btl,ug,to.mhuxi:F:/usr/spool/outnews/mhuxi 3.6  Senduuname senduuname       (no arguments) The   "uuname"   program is run, and the output is mailed to the  author  of the control message (Reply-to, if present, otherwise From).  This program lists all uucp neighbors of the  local site.  This information is used to make maps of the UUCP network.  The sys file is not  the  same  as  the UUCP   L.sys   file.   The  L.sys  file  should  never  be transmitted to another party without the  consent  of  the sites whose passwords are listed therein. It is optional for a site  to  provide  this  information. Some  reply  should  be  made to the author of the control message, so that a transmission error won't be blamed.  It is  also  permissible for a site to run the uuname program (or in some other way determine the   uucp  neighbors)  and edit  the output, either automatically or manually, before mailing the reply back to the  author.   The  file  should contain  one  site  per line, beginning with the uucp site name.  Additional information may be  included,  separated from the site name by a blank or tab.  The phone number or password for the site should NOT be included, as the reply is  considered  to  be  in the public domain.   (The uuname program will send only the site name and  not  the  entire contents  of  the  L.sys  file,  thus,  phone  numbers and passwords are not transmitted.) The purpose of this message is to  generate  and  maintain UUCP mail routing maps.  Thus, connections over which mail can be sent using the site!user syntax should be included, regardless  of whether the link is actually a UUCP link at the physical level.  If a mail router should  use  it,  it should   be  included.   Since  all  information  sent  in response to this message is optional, sites  are  free  to edit  the  list,  deleting secret or private links they do not wish to publicise. 3.7  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 article (Reply-to if present, otherwise From). - 13 - four 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 ARPANET, 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 article, 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 article on the standard input.) It is not  a  requirement  that  USENET  sites  have  mail systems  capable  of  understanding the ARPA 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  site 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  site  generating  or  forwarding  news messages must have an internet address that allows them to receive mail from sites 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 article 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". It is important that the article be sent  via  a  reliable mechansim, 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  article  will   never   be delivered.   If the article 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 article 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. - 14 - 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 article.  Another  problem  is  that  error  messages caused  by  the  mail  transmission  would  be sent to the originator of the news article, who has  no  control  over news  transmission  between two cooperating hosts and does not know who  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 article  into a mail message, such that the entire article (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 article,  and  then  attaching  whatever  mail headers  are convenient to generate.  The N's are attached to prevent any special lines  in  the  news  article  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 article.  A program on the  receiving  machine  receives  mail  to     "rnews", extracting  the  article itself and invoking the    "rnews"  program.  An example in this format might look like this: Date: Monday, 3-Jan-83 08:33:47 MST From:  news@cbosgd.UUCP Subject: network news article To:  rnews@npois.UUCP NRelay-Version: B 2.10  2/13/83 cbosgd.UUCP NPosting-Version: B 2.9 6/21/82 sask.UUCP NPath: cbosgd!mhuxj!harpo!utah-cs!sask!derek NFrom:  derek@sask.UUCP  (Derek Andrew) NNewsgroups: net.test NSubject: necessary test NMessage-ID: < 176@sask.UUCP > NDate: Monday, 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  article) and makes it harder for software to give different priorities  to  news and mail. - 15 - 4.3  Batching Since news articles are usually short, and since  a  large number  of  messages are often sent between two sites in a day, it may make sense to batch  news  articles.   Several articles  can  be  combined  into one large article, using conventions agreed upon in advance by the two sites.   One such  batching  scheme is described here; its use is still considered experimental. News articles are combined into a script, separated  by  a header of the form: ##!  rnews 1234 where 1234 is the length, in bytes, of the article.   Each such  line  is followed by an article containing the given number of bytes.   (The newline at the end of each line  of the  article  is counted as one byte, for purposes of this count, even if it is stored as CRLF.) For example, a batch of articles might look like this: #!  rnews 374 Relay-Version: version B 2.10 2/13/83; site cbosgd.UUCP Posting-Version: version B 2.10 2/13/83; site eagle.UUCP Path: cbosgd!mhuxj!mhuxt!eagle!jerry From:  jerry@eagle.uucp  (Jerry Schwarz) Newsgroups: net.general Subject: Usenet Etiquette -- Please Read Message-ID: < 642@eagle.UUCP > Date: Friday, 19-Nov-82 16:14:55 EST Here is an important message about USENET Etiquette. #!  rnews 378 Relay-Version: version B 2.10 2/13/83; site cbosgd.UUCP Posting-Version: version B 2.10 2/13/83; site eagle.UUCP Path: cbosgd!mhuxj!mhuxt!eagle!jerry From:  jerry@eagle.uucp  (Jerry Schwarz) Newsgroups: net.followup Subject: Notes on Etiquette article Message-ID: < 643@eagle.UUCP > Date: Friday, 19-Nov-82 17:24:12 EST 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. - 16 - five The News Propagation Algorithm This section describes the overall scheme  of  USENET  and the algorithm followed by sites in propagating news to the entire  network.   Since  all  sites   are   affected   by incorrectly  formatted articles 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,  each  arc  in the graph is a transmission path from one host to another host.  Each arc is  labelled with  a  newsgroup  pattern,  specifying  which  newsgroup classes are forwarded along  that  link.   Most  arcs  are bidirectional,  that  is,  if  site  A  sends  a  class of newsgroups to site B, then site B usually sends  the  same class  of  newsgroups to site A.  This bidirectionality is not, however, required. USENET is made up of many subnetworks.  Each subnet has  a name,  such  as    "net"   or   "btl".    The special subnet "net"    is defined to be USENET, although the union of all subnets may be a superset of USENET (because of sites that get local newsgroup classes but do not get net.all).  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 sites to be unable to post articles reaching the rest of the network.) An  article  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 site  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 sites  receiving  the  incoming article examine it to make sure they really want the article, accept it locally,  and then  in  turn forward the article to all their interest neighbors.   This  process  continues  until  the   entire network has seen the article. 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 site  A  sends an  article to site B, site B will send it back to site A, which will send it to site B, and so on.  One solution  to this  is  the history mechanism.  Each site keeps track of all articles  it  has  seen   (by   their  message  ID)  and whenever an article comes in that it has already seen, the incoming article is discarded immediately.  This  solution is   sufficient   to   prevent   loops,   but   additional optimizations can be made to  avoid  sending  articles  to sites that will simply throw them away. - 17 - One optimization is that an article 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 article originated on site A, then site  A has   already  seen  the  article.    (Origination  can  be determined by the Posting-Version line.) Thus, if an article is posted to  newsgroup     "net.misc", it  will match the pattern   "net.all"  (where  "all"  is a metasymbol that matches any string), and will be forwarded to  all  sites that subscribe to net.all (as determined by what their neighbors send them).  These sites make up  the "net"    subnetwork.   An article posted to    "btl.general"  will reach all sites receiving   "btl.all",  but  will  not reach  sites  that do not get   "btl.all".    In effect, the articles  reaches  the    "btl"    subnetwork.   An  article posted  to newsgroups   "net.micro,btl.general"  will reach all sites subscribing to either of the two classes. - 18 -