Re: [Lsr] Proposed Errata for RFCs 8919/8920

["Les Ginsberg (ginsberg)" <[e-mail]>]

Shraddha -

I believe we are in agreement on when zero length ABM ASLA sub-TLVs can be used and when they cannot.

The new text we proposed is:

"Link attributes MAY be advertised associated with zero-length Application Identifier Bit Masks for both standard applications and user-defined applications.
Such advertisements MUST be used by standard applications and/or user defined applications when no link attribute advertisements with a non-zero-length
Application Identifier Bit Mask and a matching Application Identifier Bit set are present for a given link. Otherwise, such advertisements MUST NOT be used."

This states both when zero-length ABM advertisements MUST be used and when they MUST NOT be used.

You have proposed different text:

"When an application specific link Attribute sub-TLV is advertised with one or more specific
standard application or user defined application bits set, all link attributes that are allowed in ASLA MUST
be used from the ASLA sub-TLVs having that specific application bit set.
For the purposes of such applications, link attributes MUST NOT be used from
ASLA sub-TLV with zero SABM & UDABM length."

This states when zero-length ABM advertisements MUST NOT be used - but it does not state when they MUST be used.
Instead, it states when non-zero length ABM advertisements MUST be used.
So this does not seem to be as complete as regards zero length ABM.

You seem to feel that there is confusion as to when non-zero ABM ASLA advertisements MUST be used - but I do not understand why that is the case.
You mention Maximum-Link-Bandwidth - for which there is a dedicated Section (4.2.1). The need for that section arises in order to make clear that different values for maximum-link-bandwidth are nonsensical and if they occur they all should be ignored.
But Section 4.2.1 also references Sections 4.2 and 6.2 to make clear that the same constraints regarding the use of zero length ABM advertisements apply to maximum-link-bandwidth.

So, I am not clear on what text is currently confusing, nor do I understand how your proposed text clarifies this confusion.

I am open to revising the proposed text - but I need more help from you to understand the source of confusion.

   Les


From: Lsr <[e-mail]> On Behalf Of Shraddha Hegde
Sent: Wednesday, June 16, 2021 7:46 AM
To: Les Ginsberg (ginsberg) <ginsberg=[e-mail]>; [e-mail]
Cc: DECRAENE Bruno IMT/OLN <[e-mail]>; Van De Velde, Gunter (Nokia - BE/Antwerp) <[e-mail]>
Subject: Re: [Lsr] Proposed Errata for RFCs 8919/8920

Hi,

I think that there may still be some ambiguity arising from the text below due to the fact that
There are attributes such as maximum-link-bandwidth which have special behaviour mentioned in later sections.

"Link attributes MAY be advertised associated with zero-length Application Identifier Bit Masks for both standard applications and user-defined applications.
Such advertisements MUST be used by standard applications and/or user defined applications when no link attribute advertisements with a non-zero-length
Application Identifier Bit Mask and a matching Application Identifier Bit set are present for a given link. Otherwise, such advertisements MUST NOT be used."


For example, If max link bandwidth attribute comes in a
Zero length SABM & UDABM and we have a Flex-algo specific ASLA
that does not have the max-link-bandwidth advertised, can
Flex-algo use max-link-bandwidth attribute?

My interpretation from modified text for ISIS is that,  it cannot use it.
I think there is no harm in re-iterating in order to avoid people reading is differently.

Link attributes MAY be advertised associated with zero-length Application Identifier Bit Masks for both standard applications and user-defined applications.
Such advertisements MUST be used by standard applications and/or user defined applications when no link attribute advertisements with a non-zero-length
Application Identifier Bit Mask and a matching Application Identifier Bit set are present for a given link. Otherwise, such advertisements MUST NOT be used.
In other words,
When an application specific link Attribute sub-TLV is advertised with one or more specific
standard application or user defined application bits set, all link attributes that are allowed in ASLA MUST
be used from the ASLA sub-TLVs having that specific application bit set.
For the purposes of such applications, link attributes MUST NOT be used from
ASLA sub-TLV with zero SABM & UDABM length.


Rgds
Shraddha



Juniper Business Use Only
From: Lsr <[e-mail]<mailto:[e-mail]>> On Behalf Of Les Ginsberg (ginsberg)
Sent: Tuesday, June 15, 2021 8:55 PM
To: [e-mail]<mailto:[e-mail]>
Cc: DECRAENE Bruno IMT/OLN <[e-mail]<mailto:[e-mail]>>; Van De Velde, Gunter (Nokia - BE/Antwerp) <[e-mail]<mailto:[e-mail]>>
Subject: [Lsr] Proposed Errata for RFCs 8919/8920

[External Email. Be cautious of content]


Folks -



Recent discussions on the list have highlighted some unintentional ambiguity in how ASLA advertisements are to be used. Please see https://mailarchive.ietf.org/arch/msg/lsr/prSLJDkMUnHm6h7VuCdn_Q7-1vg/<https://urldefense.com/v3/__https:/mailarchive.ietf.org/arch/msg/lsr/prSLJDkMUnHm6h7VuCdn_Q7-1vg/__;!!NEt6yMaO-gk!RK_eZNNu1y0aJvAqIaNwHTIFAjHWFJwW1UqyOO8ACxB0kof3jmD_dRkiPkbVLJyA$>



The following proposed Errata address this ambiguity and aligns language in the two RFCs.



We welcome comments on the proposed Errata before officially filing them.



  Les and Peter


Errata Explanation

Both RFC 8919 and RFC 8920 define advertising link attributes with zero length Standard Application Bit Mask (SABM) and zero length User Defined Application Bit Mask (UDABM)
as a means of advertising link attributes that can be used by any application. However, the text uses the word "permitted", suggesting that the use of such advertisements is "optional".
Such an interpretation could lead to interoperability issues and is not what was intended.

The replacement text below makes explicit the specific conditions when such advertisements MUST be used and the specific conditions under which they MUST NOT be used.

RFC 8919 Section 4.2:

OLD

"If link attributes are advertised associated with zero-length Application Identifier Bit Masks for both standard applications and user-defined applications,
then any standard application and/or any user-defined application is permitted to use that set of link attributes so long as there is not another set of attributes
advertised on that same link that is associated with a non-zero-length Application Identifier Bit Mask with a matching Application Identifier Bit set."

NEW

"Link attributes MAY be advertised associated with zero-length Application Identifier Bit Masks for both standard applications and user-defined applications.
Such advertisements MUST be used by standard applications and/or user defined applications when no link attribute advertisements with a non-zero-length
Application Identifier Bit Mask and a matching Application Identifier Bit set are present for a given link. Otherwise, such advertisements MUST NOT be used."

RFC 8919 Section 6.2

OLD

"Link attribute advertisements associated with zero-length Application Identifier Bit Masks for both standard applications and user-defined applications are usable
by any application, subject to the restrictions specified in Section 4.2. If support for a new application is introduced on any node in a network in the presence of such
advertisements, these advertisements are permitted to be used by the new application. If this is not what is intended, then existing advertisements MUST be readvertised
with an explicit set of applications specified before a new application is introduced."


NEW

"Link attribute advertisements associated with zero-length Application Identifier Bit Masks for both standard applications and user-defined applications are usable
by any application, subject to the restrictions specified in Section 4.2. If support for a new application is introduced on any node in a network in the presence of such
advertisements, the new application will use these advertisements, when the aforementioned restrictions are met. If this is not what is intended, then existing
advertisements MUST be readvertised with an explicit set of applications specified before a new application is introduced."



RFC 8920 Section 5

OLD

"If link attributes are advertised with zero-length Application Identifier Bit Masks for both standard applications and user-defined applications,
then any standard application and/or any user-defined application is permitted to use that set of link attributes. If support for a new application
is introduced on any node in a network in the presence of such advertisements, these advertisements are permitted to be used by the new
application. If this is not what is intended, then existing advertisements MUST be readvertised with an explicit set of applications specified
before a new application is introduced.

An application-specific advertisement (Application Identifier Bit Mask with a matching Application Identifier Bit set) for an attribute MUST
always be preferred over the advertisement of the same attribute with the zero-length Application Identifier Bit Masks for both standard
applications and user-defined applications on the same link."

NEW

"Link attributes MAY be advertised associated with zero-length Application Identifier Bit Masks for both standard applications and user-defined applications.
Such advertisements MUST be used by standard applications and/or user defined applications when no link attribute advertisements with a non-zero-length
Application Identifier Bit Mask and a matching Application Identifier Bit set are present for a given link. Otherwise, such advertisements MUST NOT be used."



RFC 8920 New Section between 12.1 and 12.2. Current sections following this new section will need to be renumbered.


12.2 Use of Zero-Length Application Identifier Bit Masks

"Link attribute advertisements associated with zero-length Application Identifier Bit Masks for both standard applications and user-defined applications are usable
by any application, subject to the restrictions specified in Section 5. If support for a new application is introduced on any node in a network in the presence of such
advertisements, the new application will use these advertisements, when the aforementioned restrictions are met. If this is not what is intended, then existing
advertisements MUST be readvertised with an explicit set of applications specified before a new application is introduced."