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1.1 ! root 1: .ds h0 "RFC xxx ! 2: .ds h1 DRAFT ! 3: .ds h2 % ! 4: .ds f0 "Standard for Interchange of USENET Messages ! 5: .ds f1 ! 6: .ds f2 "October 20, 1986 ! 7: .mt ! 8: Standard for Interchange of USENET Messages ! 9: [Obsoletes RFC 850] ! 10: .au ! 11: Mark R. Horton ! 12: .ai ! 13: AT&T Bell Laboratories ! 14: Columbus, OH 43213 ! 15: .au ! 16: Revised for B 2.11 news by Rick Adams ! 17: .hn ! 18: Introduction ! 19: .pg ! 20: This document defines the standard format for the interchange ! 21: of network News messages among USENET hosts. ! 22: It describes the format for messages themselves, ! 23: and gives partial standards for transmission of news. ! 24: The news transmission is not entirely standardized ! 25: in order to give a good deal of flexibility ! 26: to the individual hosts to choose transmission hardware and software, ! 27: whether to batch news, ! 28: and so on. ! 29: .pg ! 30: There are five sections to this document. ! 31: Section two defines the format. ! 32: Section three defines the valid control messages. ! 33: Section four specifies some valid transmission methods. ! 34: Section five describes the overall news propagation algorithm. ! 35: .hn ! 36: Message Format ! 37: .pg ! 38: The primary consideration in choosing a message format is ! 39: that it fit in with existing tools as well as possible. ! 40: Existing tools include both implementations of mail and news. ! 41: (The ! 42: .i notesfiles ! 43: system from the University of Illinois ! 44: is considered a news implementation.) ! 45: A standard format for mail messages has existed for many years on the ARPANET, ! 46: and this format meets most of the needs of USENET. ! 47: Since the ARPANET format is extensible, ! 48: extensions to meet the additional needs of USENET ! 49: are easily made within the ARPANET standard. ! 50: Therefore, ! 51: the rule is adopted that all USENET news messages ! 52: must be formatted as valid ARPANET mail messages, ! 53: according to the ARPANET standard RFC 822. ! 54: This standard is more restrictive than the ARPANET standard, ! 55: placing additional requirements on each message ! 56: and forbidding use of certain ARPANET features. ! 57: However, ! 58: it should always be possible to use a tool ! 59: expecting an ARPANET message to process a news message. ! 60: In any situation where this standard conflicts with the ARPANET standard, ! 61: RFC 822 should be considered correct and this standard in error. ! 62: .pg ! 63: An example message is included to illustrate the fields. ! 64: .sd ! 65: From: [email protected] (Jerry Schwarz) ! 66: Path: cbosgd!mhuxj!mhuxt!eagle!jerry ! 67: Newsgroups: news.announce ! 68: Subject: Usenet Etiquette -- Please Read ! 69: Message-ID: <[email protected]> ! 70: Date: Fri, 19 Nov 82 16:14:55 GMT ! 71: Followup-To: news.misc ! 72: Expires: Sat, 1 Jan 83 00:00:00 -0500 ! 73: Organization: AT&T Bell Laboratories, Murray Hill ! 74: ! 75: The body of the message comes here, after a blank line. ! 76: .ed ! 77: Here is an example of a message in the old format ! 78: (before the existence of this standard). ! 79: It is recommended that implementations also accept messages ! 80: in this format to ease upward conversion. ! 81: .sd ! 82: From: cbosgd!mhuxj!mhuxt!eagle!jerry (Jerry Schwarz) ! 83: Newsgroups: news.misc ! 84: Title: Usenet Etiquette -- Please Read ! 85: Article-I.D.: eagle.642 ! 86: Posted: Fri Nov 19 16:14:55 1982 ! 87: Received: Fri Nov 19 16:59:30 1982 ! 88: Expires: Mon Jan 1 00:00:00 1990 ! 89: ! 90: The body of the message comes here, after a blank line. ! 91: .ed ! 92: Some news systems transmit news in the ! 93: .pa A ! 94: format, ! 95: which looks like this: ! 96: .sd ! 97: Aeagle.642 ! 98: news.misc ! 99: cbosgd!mhuxj!mhuxt!eagle!jerry ! 100: Fri Nov 19 16:14:55 1982 ! 101: Usenet Etiquette - Please Read ! 102: The body of the message comes here, with no blank line. ! 103: .ed ! 104: .pg ! 105: A message consists of several header lines, ! 106: followed by a blank line, ! 107: followed by the body of the message. ! 108: The header lines consist of a keyword, ! 109: a colon, ! 110: a blank, ! 111: and some additional information. ! 112: This is a subset of the ARPANET standard, ! 113: simplified to allow simpler software to handle it. ! 114: The ! 115: .hf From ! 116: line may optionally include a full name, ! 117: in the format above, ! 118: or use the ARPANET angle bracket syntax. ! 119: To keep the implementations simple, ! 120: other formats ! 121: (for example, ! 122: with part of the machine address after the close parenthesis) ! 123: are not allowed. ! 124: The ARPANET convention of continuation header lines ! 125: (beginning with a blank or tab) ! 126: is allowed. ! 127: .pg ! 128: Certain headers are required, ! 129: and certain other headers are optional. ! 130: Any unrecognized headers are allowed, ! 131: and will be passed through unchanged. ! 132: The required headers are ! 133: .hf From , ! 134: .hf Date , ! 135: .hf Newsgroups , ! 136: .hf Subject , ! 137: .hf Message-ID , ! 138: and ! 139: .hf Path . ! 140: The optional headers are ! 141: .hf Followup-To , ! 142: .hf Expires , ! 143: .hf Reply-To , ! 144: .hf Sender , ! 145: .hf References , ! 146: .hf Control , ! 147: .hf Distribution , ! 148: .hf Keywords , ! 149: .hf Summary , ! 150: .hf Approved , ! 151: .hf Lines , ! 152: .hf Xref , ! 153: and ! 154: .hf Organization . ! 155: .hn 2 ! 156: Required Headers ! 157: .hn 3 ! 158: From ! 159: .pg ! 160: The ! 161: .hf From ! 162: line contains the electronic mailing address of the person who sent the message, ! 163: in the ARPA internet syntax. ! 164: It may optionally also contain the full name of the person, ! 165: in parentheses, ! 166: after the electronic address. ! 167: The electronic address is the same as the entity responsible ! 168: for originating the message, ! 169: unless the ! 170: .hf Sender ! 171: header is present, ! 172: in which case the ! 173: .hf From ! 174: header might not be verified. ! 175: Note that in all host and domain names, ! 176: upper and lower case are considered the same, ! 177: thus ! 178: .cf [email protected] , ! 179: .cf [email protected] , ! 180: and ! 181: .cf [email protected] ! 182: are all equivalent. ! 183: User names may or may not be case sensitive, for example, ! 184: .cf [email protected] ! 185: might be different from ! 186: .cf [email protected] . ! 187: Programs should avoid changing the case of electronic addresses ! 188: when forwarding news or mail. ! 189: .pg ! 190: RFC 822 specifies that all text in parentheses is to be interpreted as a comment. ! 191: It is common in ARPANET mail to place the full name of the user ! 192: in a comment at the end of the ! 193: .hf From ! 194: line. ! 195: This standard specifies a more rigid syntax. ! 196: The full name is not considered a comment, ! 197: but an optional part of the header line. ! 198: Either the full name is omitted, ! 199: or it appears in parentheses after the electronic address ! 200: of the person posting the message, ! 201: or it appears before an electronic address which is enclosed in angle brackets. ! 202: Thus, ! 203: the three permissible forms are: ! 204: .sd ! 205: From: [email protected] ! 206: From: [email protected] (Mark Horton) ! 207: From: Mark Horton <[email protected]> ! 208: .ed ! 209: Full names may contain any printing ASCII characters from space through tilde, ! 210: except that they may not contain ! 211: \&\*(lq(\*(rq (left parenthesis), ! 212: \&\*(lq)\*(rq (right parenthesis), ! 213: \&\*(lq<\*(rq (left angle bracket), ! 214: or \*(lq>\*(rq (right angle bracket). ! 215: Additional restrictions may be placed on full names by the mail standard, ! 216: in particular, ! 217: the characters ! 218: \&\*(lq,\*(rq (comma), ! 219: \&\*(lq:\*(rq (colon), ! 220: \&\*(lq@\*(rq (at), ! 221: \&\*(lq!\*(rq (bang), ! 222: \&\*(lq/\*(rq (slash), ! 223: \&\*(lq=\*(rq (equal), ! 224: and \*(lq;\*(rq (semicolon) are inadvisable in full names. ! 225: .hn 3 ! 226: Date ! 227: .pg ! 228: The ! 229: .hf Date ! 230: line (formerly ! 231: .hf Posted ) ! 232: is the date, ! 233: in a format that must be acceptable both to the ARPANET ! 234: and to the ! 235: .i getdate (3) ! 236: routine, ! 237: that the message was originally posted to the network. ! 238: This date remains unchanged as the message is propagated ! 239: throughout the network. ! 240: One format that is acceptable to both is: ! 241: .sd c ! 242: \f2Wdy\fP, \f2DD\fP\ \f2Mon\fP\ \f2YY\fP \f2HH\fP:\f2MM\fP:\f2SS\fP \f2TIMEZONE\fP ! 243: .ed ! 244: Several examples of valid dates appear in the sample ! 245: message above. ! 246: Note in particular that ! 247: .i ctime (3) ! 248: format: ! 249: .sd c ! 250: \f2Wdy\fP \f2Mon\fP \f2DD\fP \f2HH\fP:\f2MM\fP:\f2SS\fP \f2YYYY\fP ! 251: .ed ! 252: is ! 253: .i not ! 254: acceptable because it is not a valid ARPANET date. ! 255: However, ! 256: since older software still generates this format, ! 257: news implementations are encouraged to accept this format ! 258: and translate it into an acceptable format. ! 259: .pg ! 260: There is no hope of having a complete list of timezones. ! 261: Universal Time (GMT), the North American timezones ! 262: (PST, PDT, MST, MDT, CST, CDT, EST, EDT) and the ! 263: +/\-hhmm offset specifed in RFC822 should be supported. ! 264: It is recommended that times in message headers be transmitted in GMT ! 265: and displayed in the local time zone. ! 266: .hn 3 ! 267: Newsgroups ! 268: .pg ! 269: The ! 270: .hf Newsgroups ! 271: line specifies the newsgroup or newsgroups in which the message belongs. ! 272: Multiple newsgroups may be specified, separated by a comma. ! 273: Newsgroups specified must all be the names of existing newsgroups, ! 274: as no new newsgroups will be created by simply posting to them. ! 275: .pg ! 276: Wildcards ! 277: .i e\f1.\fPg ., ( ! 278: the word ! 279: .ng all) ! 280: are never allowed in a ! 281: .hf Newsgroups ! 282: line. ! 283: For example, ! 284: a newsgroup ! 285: .ng comp.all ! 286: is illegal, ! 287: although a newsgroup name ! 288: .ng rec.sport.football ! 289: is permitted. ! 290: .pg ! 291: If a message is received with a ! 292: .hf Newsgroups ! 293: line listing some valid newsgroups and some invalid newsgroups, ! 294: a host should not remove invalid newsgroups from the list. ! 295: Instead, ! 296: the invalid newsgroups should be ignored. ! 297: For example, ! 298: suppose host ! 299: .cn A ! 300: subscribes to the classes ! 301: .ng btl.all ! 302: and ! 303: .ng comp.all , ! 304: and exchanges news messages with host ! 305: .cn B , ! 306: which subscribes to ! 307: .ng comp.all ! 308: but not ! 309: .ng btl.all . ! 310: Suppose ! 311: .cn A ! 312: receives a message with ! 313: .sd c ! 314: Newsgroups: comp.unix,btl.general ! 315: .ed ! 316: This message is passed on to ! 317: .cn B ! 318: because ! 319: .cn B ! 320: receives ! 321: .ng comp.unix , ! 322: but ! 323: .cn B ! 324: does not receive ! 325: .ng btl.general . ! 326: .cn A ! 327: must leave the ! 328: .hf Newsgroups ! 329: line unchanged. ! 330: If it were to remove ! 331: .ng btl.general , ! 332: the edited header could eventually re-enter the ! 333: .ng btl.all ! 334: class, ! 335: resulting in a message that is not shown to users subscribing to ! 336: .ng btl.general . ! 337: Also, ! 338: follow-ups from outside ! 339: .ng btl.all ! 340: would not be shown to such users. ! 341: .hn 3 ! 342: Subject ! 343: .pg ! 344: The ! 345: .hf Subject ! 346: line ! 347: (formerly ! 348: .hf Title ) ! 349: tells what the message is about. ! 350: It should be suggestive enough of the contents of the message ! 351: to enable a reader to make a decision whether to read the message ! 352: based on the subject alone. ! 353: If the message is submitted in response to another message ! 354: .i e\f1.\fPg ., ( ! 355: is a ! 356: .i follow-up ) ! 357: the default subject should begin with the four characters \*(lqRe: \*(rq ! 358: and the ! 359: .hf References ! 360: line is required. ! 361: For follow-ups, the use of the ! 362: .hf Summary ! 363: line is encouraged. ! 364: .hn 3 ! 365: Message-ID ! 366: .pg ! 367: The ! 368: .hf Message-ID ! 369: line gives the message a unique identifier. ! 370: The Message-ID may not be reused during the lifetime of any previous message ! 371: with the same Message-ID. ! 372: (It is recommended that no Message-ID be reused for at least two years.) ! 373: Message-ID's have the syntax ! 374: .sd c ! 375: <\f2string not containing blank or \*(lq>\*(rq\fP> ! 376: .ed ! 377: In order to conform to RFC 822, ! 378: the Message-ID must have the format ! 379: .sd c ! 380: <\f2unique\fP@\f2full_domain_name\fP> ! 381: .ed ! 382: where ! 383: .i "full_domain_name" ! 384: is the full name of the host at which the message entered the network, ! 385: including a domain that host is in, ! 386: and ! 387: .i unique ! 388: is any string of printing ASCII characters, ! 389: not including ! 390: \*(lq<\*(rq (left angle bracket), ! 391: \*(lq>\*(rq (right angle bracket), ! 392: or \*(lq@\*(rq (at sign). ! 393: For example, ! 394: the ! 395: .i unique ! 396: part could be an integer representing a sequence number ! 397: for messages submitted to the network, ! 398: or a short string derived from the date and time the message was created. ! 399: For example, ! 400: a valid Message-ID for a message submitted from host ! 401: .cn ucbvax ! 402: in domain ! 403: .cf Berkeley.EDU ! 404: would be ! 405: .cf <[email protected]> . ! 406: Programmers are urged not to make assumptions ! 407: about the content of Message-ID fields from other hosts, ! 408: but to treat them as unknown character strings. ! 409: It is not safe, ! 410: for example, ! 411: to assume that a Message-ID will be under 14 characters, ! 412: that it is unique in the first 14 characters, nor that ! 413: is does not contain a \*(lq/\*(rq. ! 414: .pg ! 415: The angle brackets are considered part of the Message-ID. ! 416: Thus, ! 417: in references to the Message-ID, ! 418: such as the ! 419: .pa ihave/sendme ! 420: and ! 421: .pa cancel ! 422: control messages, ! 423: the angle brackets are included. ! 424: White space characters ! 425: .i e\f1.\fPg ., ( ! 426: blank and tab) ! 427: are not allowed in a Message-ID. ! 428: Slashes (\*(lq/\*(rq) are strongly discouraged. ! 429: All characters between the angle brackets must be printing ASCII characters. ! 430: .hn 3 ! 431: Path ! 432: .pg ! 433: This line shows the path the message took to reach the current system. ! 434: When a system forwards the message, ! 435: it should add its own name to the list of systems in the ! 436: .hf Path ! 437: line. ! 438: The names may be separated by any punctuation character or characters ! 439: (except \*(lq.\*(rq which is considered part of the hostname). ! 440: Thus, the following are valid entries: ! 441: .sd c ! 442: cbosgd!mhuxj!mhuxt ! 443: cbosgd, mhuxj, mhuxt ! 444: @cbosgd.ATT.COM,@mhuxj.ATT.COM,@mhuxt.ATT.COM ! 445: teklabs, zehntel, sri-unix@cca!decvax ! 446: .ed ! 447: (The latter path indicates a message that passed through ! 448: .cn decvax , ! 449: .cn cca , ! 450: .cn sri-unix , ! 451: .cn zehntel , ! 452: and ! 453: .cn teklabs , ! 454: in that order.) ! 455: Additional names should be added from the left. ! 456: For example, ! 457: the most recently added name in the third example was ! 458: .cn teklabs . ! 459: Letters, ! 460: digits, ! 461: periods and hyphens are considered part of host names; ! 462: other punctuation, ! 463: including blanks, ! 464: are considered separators. ! 465: .pg ! 466: Normally, ! 467: the rightmost name will be the name of the originating system. ! 468: However, ! 469: it is also permissible to include an extra entry on the right, ! 470: which is the name of the sender. ! 471: This is for upward compatibility with older systems. ! 472: .pg ! 473: The ! 474: .hf Path ! 475: line is not used for replies, ! 476: and should not be taken as a mailing address. ! 477: It is intended to show the route ! 478: the message traveled to reach the local host. ! 479: There are several uses for this information. ! 480: One is to monitor USENET routing for performance reasons. ! 481: Another is to establish a path to reach new hosts. ! 482: Perhaps the most important use is to cut down on redundant USENET traffic ! 483: by failing to forward a message to a host that is ! 484: known to have already received it. ! 485: In particular, when host ! 486: .cn A ! 487: sends a message to host ! 488: .cn B , ! 489: the ! 490: .hf Path ! 491: line includes ! 492: .cn A , ! 493: so that host ! 494: .cn B ! 495: will not immediately send the message back to host ! 496: .cn A . ! 497: The name each host uses to identify itself should be ! 498: the same as the name by which its neighbors know it, ! 499: in order to make this optimization possible. ! 500: .pg ! 501: A host adds its own name to the front of a path ! 502: when it receives a message from another host. ! 503: Thus, if a message with path ! 504: .cf A!X!Y!Z ! 505: is passed from host ! 506: .cn A ! 507: to host ! 508: .cn B , ! 509: .cn B ! 510: will add its own name to the path when it receives the message from ! 511: .cn A , ! 512: .i e\f1.\fPg ., ! 513: .cf \*(lqB!A!X!Y!Z\*(rq . ! 514: If ! 515: .cn B ! 516: then passes the message on to ! 517: .cn C , ! 518: the message sent to ! 519: .cn C ! 520: will contain the path ! 521: .cf B!A!X!Y!Z , ! 522: and when ! 523: .cn C ! 524: receives it, ! 525: .cn C ! 526: will change it to ! 527: .cf C!B!A!X!Y!Z . ! 528: .pg ! 529: Special upward compatibility note: ! 530: Since the ! 531: .hf From , ! 532: .hf Sender , ! 533: and ! 534: .hf Reply-To ! 535: lines are in internet format, ! 536: and since many USENET hosts do not yet have mailers ! 537: capable of understanding internet format, ! 538: it would break the reply capability to completely sever the connection ! 539: between the ! 540: .hf Path ! 541: header and the reply function. ! 542: It is recognized that the path is not always a valid reply string ! 543: in older implementations, ! 544: and no requirement to fix this problem is placed on implementations. ! 545: However, ! 546: the existing convention of placing the host name and an ! 547: .cf ! ! 548: at the front of the path, ! 549: and of starting the path with the host name, ! 550: an ! 551: .cf ! , ! 552: and the user name, ! 553: should be maintained when possible. ! 554: .hn 2 ! 555: Optional Headers ! 556: .hn 3 ! 557: Reply-To ! 558: .pg ! 559: This line has the same format as ! 560: .hf From . ! 561: If present, ! 562: mailed replies to the author should be sent to the name given here. ! 563: Otherwise, ! 564: replies are mailed to the name on the ! 565: .hf From ! 566: line. ! 567: (This does not prevent additional copies from being sent to recipients ! 568: named by the replier, ! 569: or on ! 570: .hf To ! 571: or ! 572: .hf Cc ! 573: lines.) ! 574: The full name may be optionally given, ! 575: in parentheses, ! 576: as in the ! 577: .hf From ! 578: line. ! 579: .hn 3 ! 580: Sender ! 581: .pg ! 582: This field is present only if the submitter manually enters a ! 583: .hf From ! 584: line. ! 585: It is intended to record the entity responsible ! 586: for submitting the message to the network. ! 587: It should be verified by the software at the submitting host. ! 588: .pg ! 589: For example, ! 590: if John Smith is visiting CCA and wishes to post a message to the network, ! 591: using friend Sarah Jones' account, ! 592: the message might read ! 593: .sd ! 594: From: [email protected] (John Smith) ! 595: Sender: [email protected] (Sarah Jones) ! 596: .ed ! 597: If a gateway program enters a mail message into the network at host ! 598: .cn unix.SRI.COM , ! 599: the lines might read ! 600: .sd ! 601: From: [email protected] ! 602: Sender: [email protected] ! 603: .ed ! 604: The primary purpose of this field is to be able to track down messages ! 605: to determine how they were entered into the network. ! 606: The full name may be optionally given, ! 607: in parentheses, ! 608: as in the ! 609: .hf From ! 610: line. ! 611: .hn 3 ! 612: Followup-To ! 613: .pg ! 614: This line has the same format as ! 615: .hf Newsgroups . ! 616: If present, ! 617: follow-up messages are to be posted ! 618: to the newsgroup or newsgroups listed here. ! 619: If this line is not present, ! 620: follow-ups are posted to the newsgroup or newsgroups listed in the ! 621: .hf Newsgroups ! 622: line. ! 623: .pg ! 624: If the keyword ! 625: .i poster ! 626: is present, follow-up messages are not permitted. The message should ! 627: be mailed to the submitter of the message via mail. ! 628: .hn 3 ! 629: Expires ! 630: .pg ! 631: This line, ! 632: if present, ! 633: is in a legal USENET date format. ! 634: It specifies a suggested expiration date for the message. ! 635: If not present, ! 636: the local default expiration date is used. ! 637: .P ! 638: This field is intended to be used to clean up ! 639: messages with a limited usefulness, ! 640: or to keep important messages around for longer than usual. ! 641: For example, ! 642: a message announcing an upcoming seminar ! 643: could have an expiration date the day after the seminar, ! 644: since the message is not useful after the seminar is over. ! 645: Since local hosts have local policies for expiration of news ! 646: (depending on available disk space, ! 647: for instance), ! 648: users are discouraged from providing expiration dates for messages ! 649: unless there is a natural expiration date associated with the topic. ! 650: System software should almost never provide a default ! 651: .hf Expires ! 652: line. ! 653: Leave it out and allow local policies to be used ! 654: unless there is a good reason not to. ! 655: .hn 3 ! 656: References ! 657: .pg ! 658: This field lists the Message-ID's of any messages prompting ! 659: the submission of this message. ! 660: It is required for all follow-up message, ! 661: and forbidden when a new subject is raised. ! 662: Implementations should provide a follow-up command, ! 663: which allows a user to post a follow-up message. ! 664: This command should generate a ! 665: .hf Subject ! 666: line which is the same as the original message, ! 667: except that if the original subject does not begin ! 668: with \*(lqRe: \*(rq or \*(lqre: \*(rq, ! 669: the four characters \*(lqRe: \*(rq are inserted before the subject. ! 670: If there is no ! 671: .hf References ! 672: line on the original header, ! 673: the ! 674: .hf References ! 675: line should contain the Message-ID of the original message ! 676: (including the angle brackets). ! 677: If the original message does have a ! 678: .hf References ! 679: line, ! 680: the follow-up message should have a ! 681: .hf References ! 682: line containing the text of the original ! 683: .hf References ! 684: line, ! 685: a blank, ! 686: and the Message-ID of the original message. ! 687: .pg ! 688: The purpose of the ! 689: .hf References ! 690: header is to allow messages to be grouped into conversations ! 691: by the user interface program. ! 692: This allows conversations within a newsgroup to be kept together, ! 693: and potentially users might shut off entire conversations ! 694: without unsubscribing to a newsgroup. ! 695: User interfaces need not make use of this header, ! 696: but all automatically generated follow-ups should generate the ! 697: .hf References ! 698: line for the benefit of systems that do use it, ! 699: and manually generated follow-ups ! 700: .i e\f1.\fPg ., ( ! 701: typed in well after the original message has been printed by the machine) ! 702: should be encouraged to include them as well. ! 703: .pg ! 704: It is permissible to not include the entire previous ! 705: .hf References ! 706: line if it is too long. An attempt should be made to include a reasonable ! 707: number of backwards references. ! 708: .hn 3 ! 709: Control ! 710: .pg ! 711: If a message contains a ! 712: .hf Control ! 713: line, ! 714: the message is a control message. ! 715: Control messages are used for communication among USENET host machines, ! 716: not to be read by users. ! 717: Control messages are distributed by the same newsgroup mechanism ! 718: as ordinary messages. ! 719: The body of the ! 720: .hf Control ! 721: header line is the message to the host. ! 722: .pg ! 723: For upward compatibility, ! 724: messages that match the newsgroup pattern ! 725: .ng all.all.ctl ! 726: should also be interpreted as control messages. ! 727: If no ! 728: .hf Control ! 729: header is present on such messages, ! 730: the subject is used as the control message. ! 731: However, ! 732: messages on newsgroups matching this pattern do not conform to this standard. ! 733: .pg ! 734: Also for upward compatibility, ! 735: if the first 4 characters of the ! 736: .hf Subject: ! 737: line are \*(lqcmsg\*(rq, the rest of the ! 738: .hf Subject: ! 739: line should be interpreted as a control message. ! 740: .hn 3 ! 741: Distribution ! 742: .pg ! 743: This line is used to alter the distribution scope of the message. ! 744: It is a comma separated list similar to the ! 745: .hf Newsgroups ! 746: line. User subscriptions are still controlled by ! 747: .hf Newsgroups , ! 748: but the message is sent to all systems subscribing to the newsgroups ! 749: on the ! 750: .hf Distribution ! 751: line in addition to the ! 752: .hf Newsgroups ! 753: line. ! 754: For the message to be transmitted, the receiving site must normally receive ! 755: one of the specified newsgroups ! 756: .b AND ! 757: must receive one of the specified distributions. ! 758: Thus, ! 759: a car for sale in New Jersey might have headers including ! 760: .sd ! 761: Newsgroups: rec.auto,misc.forsale ! 762: Distribution: nj,ny ! 763: .ed ! 764: so that it would only go to persons subscribing to ! 765: .ng rec.auto ! 766: or ! 767: .ng misc.forsale ! 768: within New Jersey or New York. ! 769: The intent of this header is to restrict the distribution of a newsgroup ! 770: further, not to increase it. A local newsgroup, such as ! 771: .ng nj.crazy-eddie , ! 772: will probably not be propagated by hosts outside New Jersey ! 773: that do not show such a newsgroup as valid. ! 774: A follow-up message should default to the same ! 775: .hf Distribution ! 776: line as the original message, but the user can change it to a more limited one, ! 777: or escalate the distribution if it was originally restricted ! 778: and a more widely distributed reply is appropriate. ! 779: .hn 3 ! 780: Organization ! 781: .pg ! 782: The text of this line is a short phrase describing the organization ! 783: to which the sender belongs, ! 784: or to which the machine belongs. ! 785: The intent of this line is to help identify the person posting the message, ! 786: since host names are often cryptic enough to make it hard ! 787: to recognize the organization by the electronic address. ! 788: .hn 3 ! 789: Keywords ! 790: .pg ! 791: A few, well selected keywords identifying the message should be on ! 792: this line. This is used as an aid in determining if this message is ! 793: interesting to the reader. ! 794: .hn 3 ! 795: Summary ! 796: .pg ! 797: This line should contain a brief summary of the message. It is ! 798: usually used as part of a follow-up to another message. Again, it is ! 799: very useful to the reader in determining whether to read the message. ! 800: .hn 3 ! 801: Approved ! 802: .pg ! 803: This line is required for any message posted to a moderated newsgroup. ! 804: It should be added by the moderator and consist of his mail address. ! 805: It is also required with certain control messages. ! 806: .hn 3 ! 807: Lines ! 808: .pg ! 809: This contains a count of the number of lines in the body of the message. ! 810: .hn 3 ! 811: Xref ! 812: .pg ! 813: This line contains the name of the host (with domains omitted) and a ! 814: white space separated list of colon separated pairs of newsgroup names ! 815: and message numbers. These are the newsgroups listed in the ! 816: .hf Newsgroups ! 817: line and the corresponding message numbers from the spool directory. ! 818: .pg ! 819: This is only of value to the local system, so it should not be transmitted. ! 820: For example, in: ! 821: .sd c ! 822: Path: seismo!lll-crg!lll-lcc!pyramid!decwrl!reid ! 823: From: [email protected] (Brian Reid) ! 824: Newsgroups: news.lists,news.groups ! 825: Subject: USENET READERSHIP SUMMARY REPORT FOR SEP 86 ! 826: Message-ID: <[email protected]> ! 827: Date: 1 Oct 86 11:26:15 GMT ! 828: Organization: DEC Western Research Laboratory ! 829: Lines: 441 ! 830: Approved: [email protected] ! 831: Xref: seismo news.lists:461 news.groups:6378 ! 832: .ed ! 833: the ! 834: .hf Xref ! 835: line shows that the message is message number 461 in the newsgroup ! 836: .b news.lists , ! 837: and message number 6378 in the newsgroup ! 838: .b news.groups , ! 839: on host ! 840: .i seismo . ! 841: This information may be used by certain user interfaces. ! 842: .hn 1 ! 843: Control Messages ! 844: .pg ! 845: This section lists the control messages currently defined. ! 846: The body of the ! 847: .hf Control ! 848: header is the control message. ! 849: Messages are a sequence of zero or more words, ! 850: separated by white space (blanks or tabs). ! 851: The first word is the name of the control message, ! 852: remaining words are parameters to the message. ! 853: The remainder of the header and the body of the message ! 854: are also potential parameters; ! 855: for example, ! 856: the ! 857: .hf From ! 858: line might suggest an address to which a response is to be mailed. ! 859: .pg ! 860: Implementors and administrators may choose to allow control messages ! 861: to be carried out automatically, ! 862: or to queue them for manual processing. ! 863: However, ! 864: manually processed messages should be dealt with promptly. ! 865: .pg ! 866: Failed control messages should NOT be mailed to the originator of the message, ! 867: but to the local \*(lqusenet\*(rq account. ! 868: .hn 2 ! 869: Cancel ! 870: .pg l ! 871: .sd ! 872: cancel <Message-ID> ! 873: .ed ! 874: If a message with the given Message-ID is present on the local system, ! 875: the message is cancelled. ! 876: This mechanism allows a user to cancel a message ! 877: after the message has been distributed over the network. ! 878: .pg ! 879: If the system is unable to cancel the message as requested, it should not ! 880: forward the cancellation request to its neighbor systems. ! 881: .pg ! 882: Only the author of the message or the local news administrator ! 883: is allowed to send this message. ! 884: The verified sender of a message is the ! 885: .hf Sender ! 886: line, ! 887: or if no ! 888: .hf Sender ! 889: line is present, ! 890: the ! 891: .hf From ! 892: line. ! 893: The verified sender of the cancel message must be the same ! 894: as either the ! 895: .hf Sender ! 896: or ! 897: .hf From ! 898: field of the original message. ! 899: A verified sender in the cancel message is allowed to match an unverified ! 900: .hf From ! 901: in the original message. ! 902: .hn 2 ! 903: Ihave/Sendme ! 904: .pg l ! 905: .sd ! 906: ihave <Message-ID list> [<remotesys>] ! 907: sendme <Message-ID list> [<remotesys>] ! 908: .ed ! 909: This message is part of the ! 910: .pa ihave/sendme ! 911: protocol, ! 912: which allows one host ! 913: (say ! 914: .cn A ) ! 915: to tell another host ! 916: .cn B ) ( ! 917: that a particular message has been received on ! 918: .cn A . ! 919: Suppose that host ! 920: .cn A ! 921: receives message ! 922: .cf <[email protected]> , ! 923: and wishes to transmit the message to host ! 924: .cn B . ! 925: .cn A ! 926: sends the control message ! 927: .cf "ihave <[email protected]> A" ! 928: to host ! 929: .cn B ! 930: (by posting it to newsgroup ! 931: .bi B ). \f3to.\fP ! 932: .cn B ! 933: responds with the control message ! 934: .cf "sendme <[email protected]> B" ! 935: (on newsgroup ! 936: .bi A ) \f3to.\fP ! 937: if it has not already received the message. ! 938: Upon receiving the ! 939: .pa sendme ! 940: message, ! 941: .cn A ! 942: sends the message to ! 943: .cn B . ! 944: .pg ! 945: This protocol can be used to cut down on redundant traffic between hosts. ! 946: It is optional and should be used ! 947: only if the particular situation makes it worthwhile. ! 948: Frequently, ! 949: the outcome is that, ! 950: since most original messages are short, ! 951: and since there is a high overhead to start sending a new message with UUCP, ! 952: it costs as much to send the ! 953: .pa ihave ! 954: as it would cost to send the message itself. ! 955: .pg ! 956: One possible solution to this overhead problem is to batch requests. ! 957: Several Message-ID's may be announced or requested in one message. ! 958: If no Message-ID's are listed in the control message, ! 959: the body of the message should be scanned for Message-ID's, ! 960: one per line. ! 961: .hn 2 ! 962: Newgroup ! 963: .sd ! 964: newgroup <groupname> [moderated] ! 965: .ed ! 966: .pg ! 967: This control message creates a new newsgroup with the given name. ! 968: Since no messages may be posted or forwarded until a newsgroup is created, ! 969: this message is required before a newsgroup can be used. ! 970: The body of the message is expected to be a short paragraph ! 971: describing the intended use of the newsgroup. ! 972: .pg ! 973: If the second argument is present and it is the keyword ! 974: .i moderated , ! 975: the group should be created moderated instead of the default of unmoderated. ! 976: The ! 977: .pa newgroup ! 978: message should be ignored unless there is an ! 979: .hf Approved ! 980: line in the same message header. ! 981: .hn 2 ! 982: Rmgroup ! 983: .sd ! 984: rmgroup <groupname> ! 985: .ed ! 986: .pg ! 987: This message removes a newsgroup with the given name. ! 988: Since the newsgroup is removed from every host on the network, ! 989: this command should be used carefully by a responsible administrator. ! 990: The rmgroup message should be ignored unless there is an ! 991: .hf Approved: ! 992: line in the same message header. ! 993: .hn 2 ! 994: Sendsys ! 995: .sd ! 996: sendsys (no arguments) ! 997: .ed ! 998: .pg ! 999: The ! 1000: .i sys ! 1001: file, ! 1002: listing all neighbors and which newsgroups are sent to each neighbor, ! 1003: will be mailed to the author of the control message ! 1004: .hf Reply-To , ( ! 1005: if present, ! 1006: otherwise ! 1007: .hf From ). ! 1008: This information is considered public information, ! 1009: and it is a requirement of membership in USENET ! 1010: that this information be provided on request, ! 1011: either automatically in response to this control message, ! 1012: or manually, ! 1013: by mailing the requested information to the author of the message. ! 1014: This information is used to keep the map of USENET up to date, ! 1015: and to determine where netnews is sent. ! 1016: .pg ! 1017: The format of the file mailed back to the author ! 1018: should be the same as that of the ! 1019: .i sys ! 1020: file. ! 1021: This format has one line per neighboring host ! 1022: (plus one line for the local host), ! 1023: containing four colon separated fields. ! 1024: The first field has the host name of the neighbor, ! 1025: the second field has a newsgroup pattern ! 1026: describing the newsgroups sent to the neighbor. ! 1027: The third and fourth fields are not defined by this standard. ! 1028: The ! 1029: .i sys ! 1030: file is ! 1031: .b not ! 1032: the same as the UUCP ! 1033: .i L.sys ! 1034: file. ! 1035: A sample response is: ! 1036: .sd ! 1037: From: cbosgd!mark (Mark Horton) ! 1038: Date: Sun, 27 Mar 83 20:39:37 -0500 ! 1039: Subject: response to your sendsys request ! 1040: To: [email protected] ! 1041: ! 1042: Responding-System: cbosgd.ATT.COM ! 1043: cbosgd:osg,cb,btl,bell,world,comp,sci,rec,talk,misc,news,soc,to,test ! 1044: ucbvax:world,comp,to.ucbvax:L: ! 1045: cbosg:world,comp,bell,btl,cb,osg,to.cbosg:F:/usr/spool/outnews/cbosg ! 1046: cbosgb:osg,to.cbosgb:F:/usr/spool/outnews/cbosgb ! 1047: sescent:world,comp,bell,btl,cb,to.sescent:F:/usr/spool/outnews/sescent ! 1048: npois:world,comp,bell,btl,ug,to.npois:F:/usr/spool/outnews/npois ! 1049: mhuxi:world,comp,bell,btl,ug,to.mhuxi:F:/usr/spool/outnews/mhuxi ! 1050: .ed ! 1051: .hn 2 ! 1052: Senduuname ! 1053: .pg l ! 1054: .sd ! 1055: senduuname (no arguments) ! 1056: .ed ! 1057: The ! 1058: .i uuname (1) ! 1059: program is run, ! 1060: and the output is mailed to the author of the control message ! 1061: .hf Reply-to , ( ! 1062: if present, ! 1063: otherwise ! 1064: .hf From ). ! 1065: This program lists all UUCP neighbors of the local host. ! 1066: This information is used to make maps of the UUCP network. ! 1067: The ! 1068: .i L.sys ! 1069: file should ! 1070: .b never ! 1071: be transmitted to another party ! 1072: without the consent of the hosts whose passwords are listed therein. ! 1073: .pg ! 1074: It is optional for a host to provide this information. ! 1075: Some reply should be made to the author of the control message, ! 1076: so that a transmission error won't be blamed. ! 1077: It is also permissible for a host to run the ! 1078: .i uuname ! 1079: program ! 1080: (or in some other way determine the UUCP neighbors) ! 1081: and edit the output, ! 1082: either automatically or manually, ! 1083: before mailing the reply back to the author. ! 1084: The file should contain one host per line, ! 1085: beginning with the UUCP host name. ! 1086: Additional information may be included, ! 1087: separated from the host name by a blank or tab. ! 1088: The phone number or password for the host should ! 1089: .ng not ! 1090: be included, ! 1091: as the reply is considered to be in the public domain. ! 1092: (The ! 1093: .i uuname ! 1094: program will send only the host name and not the entire contents of the ! 1095: .i L.sys ! 1096: file, ! 1097: thus, ! 1098: phone numbers and passwords are not transmitted.) ! 1099: .pg ! 1100: The purpose of this message was to generate and maintain UUCP mail routing maps. ! 1101: Thus, connections over which mail can be sent using the ! 1102: .cf host!user ! 1103: syntax should be included, ! 1104: regardless of whether the link is actually a UUCP link at the physical level. ! 1105: If a mail router should use it, ! 1106: it should be included. ! 1107: Since all information sent in response to this message is optional, ! 1108: hosts are free to edit the list, ! 1109: deleting secret or private links they do not wish to publicize. ! 1110: This control message is not used any more. ! 1111: .hn 2 ! 1112: Version ! 1113: .pg l ! 1114: .sd ! 1115: version (no arguments) ! 1116: .ed ! 1117: The name and version of the software running on the local system ! 1118: is to be mailed back to the author of the message ! 1119: .hf Reply-to "" ( ! 1120: if present, ! 1121: otherwise ! 1122: .hf From ). ! 1123: .hn 2 ! 1124: checkgroups ! 1125: .pg ! 1126: The message body is a list of \*(lqofficial\*(rq newsgroups and their ! 1127: description, one group per line. They are compared against the list ! 1128: of active newsgroups on the current host. The names of any obsolete or new ! 1129: newsgroups are mailed to the user \*(lqusenet\*(rq and descriptions of the ! 1130: new newsgroups are added to the help file used when posting news. ! 1131: .hn 1 ! 1132: Transmission Methods ! 1133: .pg ! 1134: USENET is not a physical network, ! 1135: but rather a logical network ! 1136: resting on top of several existing physical networks. ! 1137: These networks include, ! 1138: but are not limited to, ! 1139: UUCP, ! 1140: the ARPANET, ! 1141: an Ethernet, ! 1142: the BLICN network, ! 1143: an NSC Hyperchannel, ! 1144: and a BERKNET. ! 1145: What is important is that two neighboring systems on USENET ! 1146: have some method to get a new message, ! 1147: in the format listed here, ! 1148: from one system to the other, ! 1149: and once on the receiving system, ! 1150: processed by the netnews software on that system. ! 1151: (On ! 1152: .ux ! 1153: systems, ! 1154: this usually means the ! 1155: .i rnews ! 1156: program being run with the message on the standard input.) ! 1157: .pg ! 1158: It is not a requirement that USENET hosts have mail systems ! 1159: capable of understanding the ARPA Internet mail syntax, ! 1160: but it is strongly recommended. ! 1161: Since ! 1162: .hf From , ! 1163: .hf Reply-To , ! 1164: and ! 1165: .hf Sender ! 1166: lines use the Internet syntax, ! 1167: replies will be difficult or impossible without an internet mailer. ! 1168: A host without an internet mailer can attempt to use the ! 1169: .hf Path ! 1170: header line for replies, ! 1171: but this field is not guaranteed to be a working path for replies. ! 1172: In any event, ! 1173: any host generating or forwarding news messages ! 1174: must have an internet address that allows them ! 1175: to receive mail from hosts with internet mailers, ! 1176: and they must include their internet address on their From line. ! 1177: .hn 2 ! 1178: Remote Execution ! 1179: .pg ! 1180: Some networks permit direct remote command execution. ! 1181: On these networks, ! 1182: news may be forwarded by spooling the ! 1183: .i rnews ! 1184: command with the message on the standard input. ! 1185: For example, ! 1186: if the remote system is called ! 1187: .cn remote , ! 1188: news would be sent over a UUCP link with the command ! 1189: .sd c ! 1190: uux \- remote!rnews ! 1191: .ed ! 1192: and on a Berknet, ! 1193: .sd c ! 1194: net \-mremote rnews ! 1195: .ed ! 1196: It is important that the message be sent via a reliable mechanism, ! 1197: normally involving the possibility of spooling, ! 1198: rather than direct real-time remote execution. ! 1199: This is because, ! 1200: if the remote system is down, ! 1201: a direct execution command will fail, ! 1202: and the message will never be delivered. ! 1203: If the message is spooled, ! 1204: it will eventually be delivered when both systems are up. ! 1205: .hn 2 ! 1206: Transfer by Mail ! 1207: .pg ! 1208: On some systems, ! 1209: direct remote spooled execution is not possible. ! 1210: However, ! 1211: most systems support electronic mail, ! 1212: and a news message can be sent as mail. ! 1213: One approach is to send a mail message ! 1214: which is identical to the news message: ! 1215: the mail headers are the news headers, ! 1216: and the mail body is the news body. ! 1217: By convention, ! 1218: this mail is sent to the user ! 1219: .i newsmail ! 1220: on the remote machine. ! 1221: .pg ! 1222: One problem with this method is that it may not be possible to convince ! 1223: the mail system that the ! 1224: .hf From ! 1225: line of the message is valid, ! 1226: since the mail message was generated by a program ! 1227: on a system different from the source of the news message. ! 1228: Another problem is that error messages caused by the mail transmission ! 1229: would be sent to the originator of the news message, ! 1230: who has no control over news transmission between two cooperating hosts ! 1231: and does not know who to contact. ! 1232: Transmission error messages should be directed to a responsible ! 1233: contact person on the sending machine. ! 1234: .pg ! 1235: A solution to this problem is to encapsulate the news message ! 1236: into a mail message, such that the entire message ! 1237: (headers and body) ! 1238: are part of the body of the mail message. ! 1239: The convention here is that such mail is sent to user ! 1240: .i rnews ! 1241: on the remote system. ! 1242: A mail message body is generated by prepending the letter ! 1243: .qp N ! 1244: to each line of the news message, ! 1245: and then attaching whatever mail headers are convenient to generate. ! 1246: The ! 1247: .qp N 's ! 1248: are attached to prevent any special lines in the news message ! 1249: from interfering with mail transmission, ! 1250: and to prevent any extra lines inserted by the mailer ! 1251: (headers, ! 1252: blank lines, ! 1253: etc.) ! 1254: from becoming part of the news message. ! 1255: A program on the receiving machine receives mail to ! 1256: .i rnews , ! 1257: extracting the message itself and invoking the ! 1258: .i rnews ! 1259: program. ! 1260: An example in this format might look like this: ! 1261: .sd ! 1262: Date: Mon, 3 Jan 83 08:33:47 MST ! 1263: From: [email protected] ! 1264: Subject: network news message ! 1265: To: [email protected] ! 1266: ! 1267: NPath: cbosgd!mhuxj!harpo!utah-cs!sask!derek ! 1268: NFrom: [email protected] (Derek Andrew) ! 1269: NNewsgroups: misc.test ! 1270: NSubject: necessary test ! 1271: NMessage-ID: <[email protected]> ! 1272: NDate: Mon, 3 Jan 83 00:59:15 MST ! 1273: N ! 1274: NThis really is a test. If anyone out there more than 6 ! 1275: Nhops away would kindly confirm this note I would ! 1276: Nappreciate it. We suspect that our news postings ! 1277: Nare not getting out into the world. ! 1278: N ! 1279: .ed ! 1280: .pg ! 1281: Using mail solves the spooling problem, ! 1282: since mail must always be spooled if the destination host is down. ! 1283: However, ! 1284: it adds more overhead to the transmission process ! 1285: (to encapsulate and extract the message) ! 1286: and makes it harder for software to give different priorities ! 1287: to news and mail. ! 1288: .hn 2 ! 1289: Batching ! 1290: .pg ! 1291: Since news messages are usually short, ! 1292: and since a large number of messages ! 1293: are often sent between two hosts in a day, ! 1294: it may make sense to batch news messages. ! 1295: Several messages can be combined into one large message, ! 1296: using conventions agreed upon in advance by the two hosts. ! 1297: One such batching scheme is described here; ! 1298: its use is highly recommended. ! 1299: .pg ! 1300: News messages are combined into a script, separated by a header of the form: ! 1301: .sd ! 1302: #! rnews 1234 ! 1303: .ed ! 1304: where ! 1305: .i 1234 ! 1306: is the length, ! 1307: in bytes, ! 1308: of the message. ! 1309: Each such line is followed by a message containing the given number of bytes. ! 1310: (The newline at the end of each line of the message is counted as one byte, ! 1311: for purposes of this count, even if it is stored as ! 1312: .qc "CARRIAGE RETURN\s+2><\s-2LINE FEED" \&.) ! 1313: For example, ! 1314: a batch of message might look like this: ! 1315: .sd ! 1316: #! rnews 239 ! 1317: From: [email protected] (Jerry Schwarz) ! 1318: Path: cbosgd!mhuxj!mhuxt!eagle!jerry ! 1319: Newsgroups: news.announce ! 1320: Subject: Usenet Etiquette -- Please Read ! 1321: Message-ID: <[email protected]> ! 1322: Date: Fri, 19 Nov 82 16:14:55 EST ! 1323: Approved: [email protected] ! 1324: ! 1325: Here is an important message about USENET Etiquette. ! 1326: #! rnews 234 ! 1327: From: [email protected] (Jerry Schwarz) ! 1328: Path: cbosgd!mhuxj!mhuxt!eagle!jerry ! 1329: Newsgroups: news.announce ! 1330: Subject: Notes on Etiquette message ! 1331: Message-ID: <[email protected]> ! 1332: Date: Fri, 19 Nov 82 17:24:12 EST ! 1333: Approved: [email protected] ! 1334: ! 1335: There was something I forgot to mention in the last message. ! 1336: .ed ! 1337: Batched news is recognized because the first character in the message is ! 1338: .qp # . ! 1339: The message is then passed to the unbatcher for interpretation. ! 1340: .pg ! 1341: The second argument (in this example ! 1342: .i rnews ), ! 1343: determines which batching scheme is being used. Cooperating hosts ! 1344: may use whatever scheme is appropriate for them. ! 1345: .hn 1 ! 1346: The News Propagation Algorithm ! 1347: .pg ! 1348: This section describes the overall scheme of USENET and the algorithm ! 1349: followed by hosts in propagating news to the entire network. ! 1350: Since all hosts are affected by incorrectly formatted messages ! 1351: and by propagation errors, ! 1352: it is important for the method to be standardized. ! 1353: .pg ! 1354: USENET is a directed graph. ! 1355: Each node in the graph is a host computer, ! 1356: and each arc in the graph is a transmission path ! 1357: from one host to another host. ! 1358: Each arc is labeled with a newsgroup pattern, ! 1359: specifying which newsgroup classes are forwarded along that link. ! 1360: Most arcs are bidirectional, ! 1361: that is, ! 1362: if host ! 1363: .cn A ! 1364: sends a class of newsgroups to host ! 1365: .cn B , ! 1366: then host ! 1367: .cn B ! 1368: usually sends the same class of newsgroups to host ! 1369: .cn A . ! 1370: This bidirectionality is not, ! 1371: however, ! 1372: required. ! 1373: .pg ! 1374: USENET is made up of many subnetworks. ! 1375: Each subnet has a name, ! 1376: such as ! 1377: .ng comp ! 1378: or ! 1379: .ng btl . ! 1380: Each subnet is a connected graph, ! 1381: that is, ! 1382: a path exists from every node to every other node in the subnet. ! 1383: In addition, ! 1384: the entire graph is ! 1385: (theoretically) ! 1386: connected. ! 1387: (In practice, ! 1388: some political considerations have caused some hosts ! 1389: to be unable to post messages reaching the rest of the network.) ! 1390: .pg ! 1391: A message is posted on one machine to a list of newsgroups. ! 1392: That machine accepts it locally, ! 1393: then forwards it to all its neighbors that are interested ! 1394: in at least one of the newsgroups of the message. ! 1395: (Site ! 1396: .cn A ! 1397: deems host ! 1398: .cn B ! 1399: to be \*(lqinterested\*(rq in a newsgroup ! 1400: if the newsgroup matches the pattern on the arc from ! 1401: .cn A ! 1402: to ! 1403: .cn B . ! 1404: This pattern is stored in a file on the ! 1405: .cn A ! 1406: machine.) ! 1407: The hosts receiving the incoming message examine it ! 1408: to make sure they really want the message, ! 1409: accept it locally, ! 1410: and then in turn forward the message to all ! 1411: .i their ! 1412: interested neighbors. ! 1413: This process continues until the entire network has seen the message. ! 1414: .pg ! 1415: An important part of the algorithm is the prevention of loops. ! 1416: The above process would cause a message to loop along a cycle forever. ! 1417: In particular, ! 1418: when host ! 1419: .cn A ! 1420: sends a message to host ! 1421: .cn B , ! 1422: host ! 1423: .cn B ! 1424: will send it back to host ! 1425: .cn A , ! 1426: which will send it to host ! 1427: .cn B , ! 1428: and so on. ! 1429: One solution to this is the history mechanism. ! 1430: Each host keeps track of all messages it has seen ! 1431: (by their Message-ID) ! 1432: and whenever a message comes in that it has already seen, ! 1433: the incoming message is discarded immediately. ! 1434: This solution is sufficient to prevent loops, ! 1435: but additional optimizations can be made to avoid sending messages to hosts ! 1436: that will simply throw them away. ! 1437: .pg ! 1438: One optimization is that a message should never be sent to a machine ! 1439: listed in the ! 1440: .hf Path ! 1441: line of the header. ! 1442: When a machine name is in the ! 1443: .hf Path ! 1444: line, ! 1445: the message is known to have passed through the machine. ! 1446: Another optimization is that, if the message originated on host ! 1447: .cn A , ! 1448: then host ! 1449: .cn A ! 1450: has already seen the message. ! 1451: .P ! 1452: Thus, ! 1453: if a message is posted to newsgroup ! 1454: .ng misc.misc , ! 1455: it will match the pattern ! 1456: .ng misc.all ! 1457: (where ! 1458: .ng all ! 1459: is a metasymbol that matches any string), ! 1460: and will be forwarded to all hosts that subscribe to ! 1461: .ng misc.all ! 1462: (as determined by what their neighbors send them). ! 1463: These hosts make up the ! 1464: .ng misc ! 1465: subnetwork. ! 1466: A message posted to ! 1467: .ng btl.general ! 1468: will reach all hosts receiving ! 1469: .ng btl.all , ! 1470: but will not reach hosts that do not get ! 1471: .ng btl.all . ! 1472: In effect, ! 1473: the messages reaches the ! 1474: .ng btl ! 1475: subnetwork. ! 1476: A messages posted to newsgroups ! 1477: .ng misc.misc,btl.general ! 1478: will reach all hosts subscribing to either of the two classes.
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