Re: [Gen-art] GenART review of draft-ietf-pwe3-redundancy-06

"Bocci, Matthew (Matthew)" <> Wed, 11 April 2012 16:31 UTC

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From: "Bocci, Matthew (Matthew)" <>
To: Martin Thomson <>
Date: Wed, 11 Apr 2012 18:31:18 +0200
Thread-Topic: GenART review of draft-ietf-pwe3-redundancy-06
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Subject: Re: [Gen-art] GenART review of draft-ietf-pwe3-redundancy-06
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On 11/04/2012 16:55, "Martin Thomson" <> wrote:

>On 11 April 2012 06:44, Bocci, Matthew (Matthew)
><> wrote:
>> MB> Yes, it's really the communication mechanisms. Those details are
>> specified in the separate, standards-track,
>> draft-ietf-pwe3-redundancy-bit, which does impact interoperability.
>> Therefore I propose updating this sentence to clarify what is out of
>> scope.
>> "The mechanism for communicating the preferential forwarding status are
>> outside the scope of this document. "
>Since you have the reference, is the reason you don't want to
>reference it that you don't want a downref?

MB> No. This is a framework/requirements document, and
the WG made a specific decision early on to separate this from the
mechanism used to convey preferential forwarding status.

>>>Section 4.1: "Non-revertive behavior MUST be supported, while
>>>revertive behavior is OPTIONAL."
>>>The reason for this requirement is non-obvious (at least to me).  Some
>>>justification for it seems appropriate.
>> MB> This is an operator requirement to ensure that the protocols
>> in support of PW redundancy at least support non-revertive operation as
>> baseline. To implement a revertive behaviour, you will need to designate
>> one of the Pws
>So you had a choice: one mandatory, but which; or both mandatory.  The
>WG chose non-revertive as the only mandatory option.  I guess I was
>(obliquely) requesting that you provide motivation in the document,
>rather than just in response to my mail.

MB> I propose modifying the paragraph as follows:

 o  Non-revertive behavior MUST be supported, while revertive behavior
      is OPTIONAL. This avoids the need to designate one PW as primary
unless revertive
behavior is explicitly required.

>>>Section 4.1:    "Protection switchover can be triggered by the operator
>> MB> This requirement does have a protocol implication, both in terms of
>> the state machine and the ability to coordinate the state at both PEs in
>> the case
>> that a manual switchover is initiated from only one PE.
>The process that you describe doesn't address that requirement.  That
>process ensures that operator intervention doesn't cause a failure by
>ensuring that the operator is unable to disable a redundant PW by
>removing the only active path.  From the protocol perspective, you
>need a mechanism for signaling that a path is being administratively
>Requirement: Protection switchover can be initiated by either PE.
>Motivation: Operator intervention may be necessary to disable one part
>of a redundant PW.
>Product requirement: Operator intervention shall not be able to
>disable a PW by disabling the only available part of a redundant PW.
>(Excuse the sloppy terminology, it's been a while and I'm too lazy to
>get this right.)
>I don't have any real problem with your explanations, but it seems to
>me at least that it could be made clearer.  Don't feel obligated to
>change on my accord alone, but there are value in being really clear
>about these requirements.

MB> I propose modifying the paragraph as follows:

  o  Protection switchover can be initiated from a PE e.g. using
      a Manual lockout/force switchover, or it may be triggered by a
      signal failure i.e. a defect in the PW or PSN. Manual switchover may
be necessary 
if it is required to disable one PW in a redundant set. Both methods MUST
      be supported and signal failure triggers MUST be treated with a
      higher priority than any local or far-end manual