rfc1661.html

ppp协议英文文档.介绍ppp的和ldc等相关协议 好东西啊

      automaton.

   Length

      The Length field is two octets, and indicates the length of the
      LCP packet, including the Code, Identifier, Length and Data
      fields.  The Length MUST NOT exceed the MRU of the link.

      Octets outside the range of the Length field are treated as
      padding and are ignored on reception.  When a packet is received
      with an invalid Length field, the packet is silently discarded
      without affecting the automaton.

   Data

      The Data field is zero or more octets, as indicated by the Length
      field.  The format of the Data field is determined by the Code
      field.

5.1.  Configure-Request

   Description

      An implementation wishing to open a connection MUST transmit a
      Configure-Request.  The Options field is filled with any desired
      changes to the link defaults.  Configuration Options SHOULD NOT be
      included with default values.

      Upon reception of a Configure-Request, an appropriate reply MUST
      be transmitted.

   A summary of the Configure-Request packet format is shown below.  The
   fields are transmitted from left to right.

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Code      |  Identifier   |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Options ...
   +-+-+-+-+

   Code

      1 for Configure-Request.

   Identifier

      The Identifier field MUST be changed whenever the contents of the
      Options field changes, and whenever a valid reply has been
      received for a previous request.  For retransmissions, the
      Identifier MAY remain unchanged.

   Options

      The options field is variable in length, and contains the list of
      zero or more Configuration Options that the sender desires to
      negotiate.  All Configuration Options are always negotiated
      simultaneously.  The format of Configuration Options is further
      described in a later chapter.

5.2.  Configure-Ack

   Description

      If every Configuration Option received in a Configure-Request is
      recognizable and all values are acceptable, then the
      implementation MUST transmit a Configure-Ack.  The acknowledged
      Configuration Options MUST NOT be reordered or modified in any
      way.

      On reception of a Configure-Ack, the Identifier field MUST match
      that of the last transmitted Configure-Request.  Additionally, the
      Configuration Options in a Configure-Ack MUST exactly match those
      of the last transmitted Configure-Request.  Invalid packets are
      silently discarded.

   A summary of the Configure-Ack packet format is shown below.  The
   fields are transmitted from left to right.

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Code      |  Identifier   |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Options ...
   +-+-+-+-+

   Code

      2 for Configure-Ack.

   Identifier

      The Identifier field is a copy of the Identifier field of the
      Configure-Request which caused this Configure-Ack.

   Options

      The Options field is variable in length, and contains the list of
      zero or more Configuration Options that the sender is
      acknowledging.  All Configuration Options are always acknowledged
      simultaneously.

5.3.  Configure-Nak

   Description

      If every instance of the received Configuration Options is
      recognizable, but some values are not acceptable, then the
      implementation MUST transmit a Configure-Nak.  The Options field
      is filled with only the unacceptable Configuration Options from
      the Configure-Request.  All acceptable Configuration Options are
      filtered out of the Configure-Nak, but otherwise the Configuration
      Options from the Configure-Request MUST NOT be reordered.

      Options which have no value fields (boolean options) MUST use the
      Configure-Reject reply instead.

      Each Configuration Option which is allowed only a single instance
      MUST be modified to a value acceptable to the Configure-Nak
      sender.  The default value MAY be used, when this differs from the
      requested value.

      When a particular type of Configuration Option can be listed more
      than once with different values, the Configure-Nak MUST include a
      list of all values for that option which are acceptable to the
      Configure-Nak sender.  This includes acceptable values that were
      present in the Configure-Request.

      Finally, an implementation may be configured to request the
      negotiation of a specific Configuration Option.  If that option is
      not listed, then that option MAY be appended to the list of Nak'd
      Configuration Options, in order to prompt the peer to include that
      option in its next Configure-Request packet.  Any value fields for
      the option MUST indicate values acceptable to the Configure-Nak
      sender.

      On reception of a Configure-Nak, the Identifier field MUST match
      that of the last transmitted Configure-Request.  Invalid packets
      are silently discarded.

      Reception of a valid Configure-Nak indicates that when a new
      Configure-Request is sent, the Configuration Options MAY be
      modified as specified in the Configure-Nak.  When multiple
      instances of a Configuration Option are present, the peer SHOULD
      select a single value to include in its next Configure-Request
      packet.

      Some Configuration Options have a variable length.  Since the
      Nak'd Option has been modified by the peer, the implementation
      MUST be able to handle an Option length which is different from

      the original Configure-Request.

   A summary of the Configure-Nak packet format is shown below.  The
   fields are transmitted from left to right.

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Code      |  Identifier   |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Options ...
   +-+-+-+-+

   Code

      3 for Configure-Nak.

   Identifier

      The Identifier field is a copy of the Identifier field of the
      Configure-Request which caused this Configure-Nak.

   Options

      The Options field is variable in length, and contains the list of
      zero or more Configuration Options that the sender is Nak'ing.
      All Configuration Options are always Nak'd simultaneously.

5.4.  Configure-Reject

   Description

      If some Configuration Options received in a Configure-Request are
      not recognizable or are not acceptable for negotiation (as
      configured by a network administrator), then the implementation
      MUST transmit a Configure-Reject.  The Options field is filled
      with only the unacceptable Configuration Options from the
      Configure-Request.  All recognizable and negotiable Configuration
      Options are filtered out of the Configure-Reject, but otherwise
      the Configuration Options MUST NOT be reordered or modified in any
      way.

      On reception of a Configure-Reject, the Identifier field MUST
      match that of the last transmitted Configure-Request.
      Additionally, the Configuration Options in a Configure-Reject MUST

      be a proper subset of those in the last transmitted Configure-
      Request.  Invalid packets are silently discarded.

      Reception of a valid Configure-Reject indicates that when a new
      Configure-Request is sent, it MUST NOT include any of the
      Configuration Options listed in the Configure-Reject.

   A summary of the Configure-Reject packet format is shown below.  The
   fields are transmitted from left to right.

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Code      |  Identifier   |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Options ...
   +-+-+-+-+

   Code

      4 for Configure-Reject.

   Identifier

      The Identifier field is a copy of the Identifier field of the
      Configure-Request which caused this Configure-Reject.

   Options

      The Options field is variable in length, and contains the list of
      zero or more Configuration Options that the sender is rejecting.
      All Configuration Options are always rejected simultaneously.

5.5.  Terminate-Request and Terminate-Ack

   Description

      LCP includes Terminate-Request and Terminate-Ack Codes in order to
      provide a mechanism for closing a connection.

      An implementation wishing to close a connection SHOULD transmit a
      Terminate-Request.  Terminate-Request packets SHOULD continue to
      be sent until Terminate-Ack is received, the lower layer indicates
      that it has gone down, or a sufficiently large number have been
      transmitted such that the peer is down with reasonable certainty.

      Upon reception of a Terminate-Request, a Terminate-Ack MUST be
      transmitted.

      Reception of an unelicited Terminate-Ack indicates that the peer
      is in the Closed or Stopped states, or is otherwise in need of
      re-negotiation.

   A summary of the Terminate-Request and Terminate-Ack packet formats
   is shown below.  The fields are transmitted from left to right.

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Code      |  Identifier   |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    Data ...
   +-+-+-+-+

   Code

      5 for Terminate-Request;

      6 for Terminate-Ack.

   Identifier

      On transmission, the Identifier field MUST be changed whenever the
      content of the Data field changes, and whenever a valid reply has
      been received for a previous request.  For retransmissions, the
      Identifier MAY remain unchanged.

      On reception, the Identifier field of the Terminate-Request is
      copied into the Identifier field of the Terminate-Ack packet.

   Data

      The Data field is zero or more octets, and contains uninterpreted
      data for use by the sender.  The data may consist of any binary
      value.  The end of the field is indicated by the Length.

5.6.  Code-Reject

   Description

      Reception of a LCP packet with an unknown Code indicates that the
      peer is operating with a different version.  This MUST be reported
      back to the sender of the unknown Code by transmitting a Code-
      Reject.

      Upon reception of the Code-Reject of a code which is fundamental
      to this version of the protocol, the implementation SHOULD report
      the problem and drop the connection, since it is unlikely that the
      situation can be rectified automatically.

   A summary of the Code-Reject packet format is shown below.  The
   fields are transmitted from left to right.

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Code      |  Identifier   |