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Label in a RESV message

  • From: "Sanford, Bill" <bill.sanford@netplane.com>
  • Date: Wed, 12 Dec 2001 16:55:02 -0500

I am confused about the label object in a RESV message.

In draft-ietf-mpls-rsvp-lsp-tunnel-09.txt, if you logically follow the
madatory objects (according to the BNF) in the RESV Message format, the
label is a mandatory object. In the note following the RESV Message and in
the next section, LSP Tunnel related Objects, it is considered to be
optional. Why wouldn't you want the label as a mandatory object? 


3.2. Resv Message

   The format of the Resv message is as follows:

      <Resv Message> ::=       <Common Header> [ <INTEGRITY> ]
                               <SESSION>  <RSVP_HOP>
                               <TIME_VALUES>
                               [ <RESV_CONFIRM> ]  [ <SCOPE> ]
                               [ <POLICY_DATA> ... ]
                               <STYLE> <flow descriptor list>

      <flow descriptor list> ::= <FF flow descriptor list>
                               | <SE flow descriptor>


      <FF flow descriptor list> ::= <FLOWSPEC> <FILTER_SPEC>
                               <LABEL> [ <RECORD_ROUTE> ]
                               | <FF flow descriptor list>
                               <FF flow descriptor>

      <FF flow descriptor> ::= [ <FLOWSPEC> ] <FILTER_SPEC> <LABEL>
                               [ <RECORD_ROUTE> ]

      <SE flow descriptor> ::= <FLOWSPEC> <SE filter spec list>

      <SE filter spec list> ::= <SE filter spec>
                               | <SE filter spec list> <SE filter spec>

      <SE filter spec> ::=     <FILTER_SPEC> <LABEL> [ <RECORD_ROUTE> ]

      Note:  LABEL and RECORD_ROUTE (if present), are bound to the
             preceding FILTER_SPEC.  No more than one LABEL and/or
             RECORD_ROUTE may follow each FILTER_SPEC.



4. LSP Tunnel related Objects

4.1. Label Object

   Labels MAY be carried in Resv messages. For the FF and SE styles, a
   label is associated with each sender.  The label for a sender MUST
   immediately follow the FILTER_SPEC for that sender in the Resv
   message.