Hi all,

In order to (try to) avoid interop issues, I have a clarification question on 
RFC 8919.

"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."
https://www.rfc-editor.org/rfc/rfc8919.html#name-application-specific-link-a

My reading is that if one ALSA "S1"  with a specific application bit set (e.g. 
X-Flag/FlexAlgo) advertises a set of attributes (A1, A2), then this ALSA (or 
the set of all ASLA occurrence with the X-Flag set) needs to advertise _all_ 
the attributes used by this application.

So:
- if we have another ALSA "S2" advertising zero-length Application Identifier 
Bit Masks for both standard applications and user-defined applications, that 
application (FlexAlgo) is not permitted to fall back to "S2" in order to learn 
a another attribute (A3). Regardless of whether S2 advertises the L-flag 
(legacy) or its own Link Attribute sub-sub-TLVs.
- if we don't have such S2 ASLA, that application (FlexAlgo) is not permitted 
to fall back to legacy attributes.

IOW, an ALSA for application X, does not advertise additional/more specific 
attributes for application X, but _all_ the attributes that application X is 
allowed to read. As a consequence, if an attribute is common to N set of 
applications, it needs to be advertised N times in N ASLA.

Thanks for correcting/confirming.

Thanks,
Regards,
Bruno


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