rfc2840.txt

著名的RFC文档,其中有一些文档是已经翻译成中文的的.


RFC 2840                  TELNET KERMIT OPTION                  May 2000


6.2. EXAMPLE 2

   The Telnet server contains a Kermit server and starts a Kermit server
   immediately after a connection is made.  The Telnet client does not
   offer a Kermit server.

   Telnet Server                   Telnet Client
   -----------------------------   -----------------------------
   <starts negotiations>
   WILL KERMIT
   DO KERMIT
                                   <responds to negotiations>
                                   DO KERMIT
                                   SB KERMIT SOP <0x01>
                                   WONT KERMIT
   SB KERMIT SOP <0x01>

   <starts Kermit Server>
   SB KERMIT START-SERVER

   At this point the Telnet client knows that a Kermit server is on the
   other end of the connection, and so may customize its command set or
   menus to allow only those commands that are valid as a client of a
   Kermit server.



























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RFC 2840                  TELNET KERMIT OPTION                  May 2000


6.3. EXAMPLE 3

   Telnet server and Telnet client both contain a Kermit server.  Telnet
   client Kermit server is active whenever its terminal emulator is
   active, and not active at other times.  The Telnet server is used for
   shell access and does not start a Kermit Server unless requested.

   Telnet Server                 Telnet Client
   ---------------------------   -----------------------------
   <starts negotiations>
   WILL KERMIT
   DO KERMIT
                                 <responds to negotiations>
                                 DO KERMIT
                                 SB KERMIT SOP <0x01>
                                 WILL KERMIT
   SB KERMIT SOP <0x01>
                                 <telnet client enters terminal emulator>
                                 SB KERMIT START-SERVER

                                 <client leaves terminal emulator>
                                 SB KERMIT STOP-SERVER

                                 <client requests Kermit service>
                                 SB KERMIT REQ-START-SERVER
   <starts Kermit server>
   SB KERMIT RESP-START-SERVER
                                 <client sends Kermit FINISH packet>
   <stops Kermit server>
   SB KERMIT STOP-SERVER
                                 <client returns to terminal emulator>
                                 SB KERMIT START-SERVER



















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RFC 2840                  TELNET KERMIT OPTION                  May 2000


6.4. EXAMPLE 4

   Telnet server and Telnet client both contain a Kermit server.  Telnet
   client's Kermit server is active whenever the terminal emulator is
   active.  Telnet server is used solely for Kermit protocol and
   automatically starts a Kermit Server upon accepting the connection.

   Telnet Server                 Telnet Client
   ---------------------------   -----------------------------
   <starts negotiations>
   WILL KERMIT
   DO KERMIT
                                 <responds to negotiations>
                                 DO KERMIT
                                 SB KERMIT SOP <0x01>
                                 WILL KERMIT

   SB KERMIT SOP <0x01>
                                 <client enters terminal emulator>
                                 SB KERMIT START-SERVER

   <in response to DO>
   SB KERMIT SOP <0x01>
   SB KERMIT START-SERVER
                                 <client restricts command set to
                                  Kermit protocol commands>
                                 SB KERMIT STOP-SERVER

                                 <client performs Kermit protocol
                                  operations>

                                 <client want to enter terminal mode>
                                 SB KERMIT REQ-STOP-SERVER

   <Kermit Server refuses>
   SB KERMIT RESP-START-SERVER















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RFC 2840                  TELNET KERMIT OPTION                  May 2000


6.5. EXAMPLE 5

   This is an example of something that should not be allowed to happen.
   Some Telnet clients that implement file transfer capabilities are
   designed to accept incoming connections.  In this situation the
   Telnet Client acts as a pseudo Telnet Server but without the ability
   to provide shell access or many of the other functions associated
   with Telnet.  If both Telnet clients support this option and contain
   a Kermit server that is active during terminal emulation there is the
   potential for a deadlock situation if scripting is also supported.
   This is because Telnet clients that support a script language do not
   process input while waiting for the next command to be issued.

   Telnet Client One             Telnet Client Two
   ---------------------------   -----------------------------
   <starts negotiations>
   WILL KERMIT
   DO KERMIT
                                 <responds to WILL>
                                 DO KERMIT
                                 SB KERMIT SOP <0x01>

   <in response to DO>
   SB KERMIT SOP <0x01>
   SB KERMIT START-SERVER
                                 <responds to DO>
                                 WILL KERMIT
                                 SB KERMIT START-SERVER

   <client one restricts command
    set to Kermit protocol and
    disables Kermit Server>
   SB KERMIT STOP-SERVER
                                 <client two restricts command
                                  set to Kermit protocol and
                                  disables Kermit Server>
                                 SB KERMIT STOP-SERVER

   At this point both clients have restricted their command set to
   Kermit Protocol commands.  However, in both cases neither side is
   processing input.  Therefore the following restriction MUST be
   enforced: A Telnet partner may not restrict the command set if it
   accepted the incoming connection.








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RFC 2840                  TELNET KERMIT OPTION                  May 2000


7. SECURITY

   Implementors of this Telnet Option must enforce appropriate user
   authentication and file system access restrictions in conjunction
   with their implementation of the Kermit file transfer protocol.
   These issues are beyond the scope of this document.

8. REFERENCES

   [BCP] Bradner, S.,  "Key words for use in RFCs to Indicate
         Requirement Levels", BCP 14, RFC 2119, March 1997.

   [KER] da Cruz, Frank, "Kermit, A File Transfer Protocol", Digital
         Press/ Butterworth Heinemann, Newton, MA, ISBN 0-932376-88-6
         (1987).

   [IKS] da Cruz, F. and J. Altman, "Internet Kermit Service", RFC 2839,
         May 2000.

   [TEL] Postel, J. and J. Reynolds, "Telnet Protocol Specification",
         STD 8, RFC 854, May 1983.

   [TEL] Postel, J. and J. Reynolds, "Telnet Option Specification", STD
         8, RFC 855, May 1983.


9. AUTHORS' ADDRESSES

   Jeffrey E. Altman

   EMail:[e-mail]


   Frank da Cruz

   EMail: [e-mail]


   The Kermit Project
   Columbia University
   612 West 115th Street
   New York NY 10025-7799
   USA
   http://www.columbia.edu/kermit/
   http://www.kermit-project.org/






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RFC 2840                  TELNET KERMIT OPTION                  May 2000


10.  Full Copyright Statement

   Copyright (C) The Internet Society (2000).  All Rights Reserved.

   This document and translations of it may be copied and furnished to
   others, and derivative works that comment on or otherwise explain it
   or assist in its implementation may be prepared, copied, published
   and distributed, in whole or in part, without restriction of any
   kind, provided that the above copyright notice and this paragraph are
   included on all such copies and derivative works.  However, this
   document itself may not be modified in any way, such as by removing
   the copyright notice or references to the Internet Society or other
   Internet organizations, except as needed for the purpose of
   developing Internet standards in which case the procedures for
   copyrights defined in the Internet Standards process must be
   followed, or as required to translate it into languages other than
   English.

   The limited permissions granted above are perpetual and will not be
   revoked by the Internet Society or its successors or assigns.

   This document and the information contained herein is provided on an
   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
   TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
   BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Acknowledgement

   Funding for the RFC Editor function is currently provided by the
   Internet Society.



















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