Re: [Lsr] Roman Danyliw's No Objection on draft-ietf-lsr-isis-invalid-tlv-02: (with COMMENT)

Roman -

Thanx for the review.
Inline.

> -----Original Message-----
> From: Lsr <lsr-bounces@ietf.org> On Behalf Of Roman Danyliw via
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> Sent: Monday, July 13, 2020 7:40 AM
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> Subject: [Lsr] Roman Danyliw's No Objection on draft-ietf-lsr-isis-invalid-tlv-
> 02: (with COMMENT)
> 
> Roman Danyliw has entered the following ballot position for
> draft-ietf-lsr-isis-invalid-tlv-02: No Objection
> 
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> ----------------------------------------------------------------------
> COMMENT:
> ----------------------------------------------------------------------
> 
> I'm glad to see language clarifying error handling.  Thanks for the work on it.
> 
> Section 3.2.  Per “It is RECOMMENDED that implementations provide controls
> for
> the enablement of behaviors that are not backward compatible”, I want to
> double
> check that I’m understanding this  sentence correctly. RFC5304 provides
> normative guidance that isn’t backward compatible with ISO10589. RFC6233
> provide guidance that isn’t backward compatible with either RFC5304 or
> ISO10589.  Is the initial sentence effectively saying that implementations
> should support deployments in configurations that are not backward
> compatible
> (i.e., those using the newer TLVs)?  As these changes are covering security
> matters, I read “controls” in the cyber mitigation sense -- they prevent an
> action, not enable one.

[Les:] The recommendation is for implementations to provide control as to when the new (non-backwards compatible) behavior is used.
Without that, an implementation which adds support for (to use one example) sending the Purge Originator TLV in the presence of MD5 authentication would simply start sending it and risk the PDU not being accepted by implementations which had not yet added the support.

One way of reading this is that "including the POI TLV in purges w MD5 authentication" is "enablement" of a new feature. Another way of reading it might be "disablement" of the use of a new feature.
This seems to me to be a semantical distinction.

The recommendation to use "controls" also does not specify what the default behavior should be - that is up to the implementation.

   Les

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