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RFC 8919, "IS-IS Application-Specific Link Attributes", October 2020

Source of RFC: lsr (rtg)

Errata ID: 6630
Status: Reported
Type: Technical
Publication Format(s) : TEXT

Reported By: Les Ginsberg
Date Reported: 2021-07-05

Throughout the document, when it says:

Section 4.2:
OLD

If the SABM or UDABM Length in the Application Identifier Bit Mask
is greater than 8, the entire sub-TLV MUST be ignored.

(Later in 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.

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.

It should say:

Section 4.2
NEW

If the SABM or UDABM Length in the Application Identifier Bit Mask
is greater than 8, the entire sub-TLV MUST be ignored.

When SABM or UDABM Length is non-zero and the L-flag is NOT set, all
applications specified in the bit mask MUST use the link attribute
advertisements in the sub-TLV.

(Later in Section 4.2)
NEW

Link attributes MAY be advertised associated with zero-length
Application Identifier Bit Masks for both standard applications and
user-defined applications. Such link attribute 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 link attribute advertisements
MUST NOT be used.

Section 6.2
NEW

Link attributes MAY be advertised associated with zero-length
Application Identifier Bit Masks for both standard applications and
user-defined applications. Such link attribute 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 link attribute advertisements
MUST NOT be used.

Notes:

RFC 8919 defines advertising link attributes with zero
length Standard Application Bit Mask (SABM) and zero length User
Defined ApplicationBit 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.

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