Hi Bruno,
On 03/06/2021 14:55, [email protected] wrote:
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.
right.
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.
yes, that is correct.
- if we don’t have such S2 ASLA, that application (FlexAlgo) is not
permitted to fall back to legacy attributes.
well, if you have S1 as you mentioned above, S2 becomes irrelevant from
the flex-algo perspective. So you are right, flex-algo is not allowed to
use legacy advertisement in this case.
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.
correct.
As a consequence, if an attribute is
common to N set of applications, it needs to be advertised N times in N
ASLA.
depends. If the set of attributes that are common across N applications
represent the full set of attributes for all these N applications, you
simply advertise them once with SAMB/UDAMB including the bits for all N
applications. If the set of attributes for each application is
different, but there is one attribute that is common, you need to
include that attribute in ASLA advertisement for every app.
thanks,
Peter
Thanks for correcting/confirming.
Thanks,
Regards,
Bruno
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