Reduced Backus-Naur Form (RBNF) A Syntax Used in Various Protocol Specifications draft-farrel-rtg-common-bnf-07.txt

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Reduced Backus-Naur Form (RBNF)A Syntax Used in
Various ProtocolSpecificationsdraft-farrel-rtg-c
ommon-bnf-07.txt

• Adrian Farrel
• adrian_at_olddog.co.uk

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Background

• Many Routing Area (and related) documents define
  messages using Backus-Naur Format (BNF)
• RSVP (RFC 2205) (Transport Area)
• RSVP-TE (RFC 3209)
• RSVP-TE for GMPLS (RFC 3473)
• LMP (RFC 4204)
• PCEP (draft-ietf-pce-pcep)
• They use a common variant of BNF that is not
  formally documented anywhere

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Why Bother?

• Protocol extensions require a host of new I-Ds
  defining extensions to messages
• Many Discusses raised during IESG review
• Where is the definition of the formal language
  you use in this document?
• Attempted answer as used in RFC 2205 was
  rejected
• It does make sense to have a standard reference
• Help people to write new documents
• Enables automatic verification of the BNF
• Help people to understand existing documents
• Do we really need this document
• Maybe, maybe not
• It does no harm and it helps the review process

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Why Not Use an Existing Reference?

• Two existing key definitions
• Extended BNF (ISO/IEC 14977)
• Augmented BNF (RFC 5234)
• It turns out that the syntax used in existing
  RFCs differs slightly from these definitions
• We could have a specification that lists the
  differences
• That would be a bit messy
• We actually only need a small subset of the full
  BNF vocabulary and grammar

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What is in the draft?

• Rules
• Objects
• Constructs
• Messages
• Operators
• Assignment
• Concatenation
• Optional Presence
• Alternatives
• Repetition
• Grouping
• Editorial Conventions
• White Space
• Line Breaks
• Ordering
• Precedence rules
• Examples

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Arent the examples a bit convoluted?

• Some of them are!
• But nearly all of them come from real RFCs
• So, dont blame me
• The examples give impetus for
• A specification that helps us interpret the RFCs
• Recommendations on how to write BNF in future

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Document Status

• First version submitted early March
• Eighth revision submitted early November
• Reviews received from a bunch of people
• Thanks!
• Review requested several times in
• CCAMP, MPLS, PCE, RTGWG, RTG Area, TSVWG
• Now ready to be an RFC
• Standards Track
• But only mandatory in documents that cite it as a
  normative reference