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Church Of The
Swimming Elephant

4.1 Message Header Format Connected: An Internet Encyclopedia
4.1 Message Header Format

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Next: 4.2 OPEN Message Format

4.1 Message Header Format

4.1 Message Header Format

Each message has a fixed-size header. There may or may not be a data portion following the header, depending on the message type. The layout of these fields is shown below:

       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
      |                                                               |
      +                                                               +
      |                                                               |
      +                                                               +
      |                           Marker                              |
      +                                                               +
      |                                                               |
      |          Length               |      Type     |


         This 16-octet field contains a value that the receiver of the
         message can predict.  If the Type of the message is OPEN, or if
         the OPEN message carries no Authentication Information (as an
         Optional Parameter), then the Marker must be all ones.
         Otherwise, the value of the marker can be predicted by some a
         computation specified as part of the authentication mechanism
         (which is specified as part of the Authentication Information)
         used.  The Marker can be used to detect loss of synchronization
         between a pair of BGP peers, and to authenticate incoming BGP


         This 2-octet unsigned integer indicates the total length of the
         message, including the header, in octets.  Thus, e.g., it
         allows one to locate in the transport-level stream the (Marker
         field of the) next message.  The value of the Length field must
         always be at least 19 and no greater than 4096, and may be
         further constrained, depending on the message type.  No
         "padding" of extra data after the message is allowed, so the
         Length field must have the smallest value required given the
         rest of the message.


         This 1-octet unsigned integer indicates the type code of the
         message.  The following type codes are defined:

                                    1 - OPEN
                                    2 - UPDATE
                                    3 - NOTIFICATION
                                    4 - KEEPALIVE

Next: 4.2 OPEN Message Format

Connected: An Internet Encyclopedia
4.1 Message Header Format


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