RFC 467 (rfc467) - Page 1 of 7

Proposed change to Host-Host Protocol: Resynchronization of connection status

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Network Working Group                                       J. Burchfiel
Request for Comments: 467                                   R. Tomlinson
NIC: 14741                                       Bolt Beranek and Newman
                                                        20 February 1973

                 Proposed Change To Host-Host Protocol
                Resynchronization Of Connection Status

I. Introduction

   The current Host-Host protocol (NIC #8246) contains no provisions for
   resynchronizing the status information kept at the two ends of each
   connection.  In particular, if either host suffers a service
   interruption, or if a control message is lost or corrupted in an
   interface or in the subnet, the status information at the two ends of
   the connection will be inconsistent.

   Since the current protocol provides no way to correct this condition,
   the NCP's at the two ends stay "confused" forever.  A frequent and
   frustrating symptom of this effect is the "lost allocate" phenomenon,
   where the receiving NCP believes that it has bit and message
   allocations outstanding, while the sending NCP believes that it does
   not have any allocation.  As a result, information flow over that
   connection can never be restarted.

   Use of the Host-Host RST (reset) command is inappropriate here, as it
   destroys all connections between the two hosts.  What is needed is a
   way to reset only the affected connection without disturbing any

   A second troublesome symptom of inconsistency in status information
   is the "half-closed" connection: after a service interruption or
   network partitioning, one NCP may believe that a connection is still
   open, while the other believes that the connection is closed. (Does
   not exist.)  When such an inconsistency is discovered, the "open" end
   of the connection should be closed.


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