Hi Peter,
Thank you for your answer and for your crystal clear email. As a side note, my reading of RFC 8920 is that this behaviour is different in OSPF. “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.” Not sure whether there was a technical reason for this difference, but it didn’t help be clarify by myself the RFC 8919 formulation. Thank you, --Bruno > -----Original Message----- > From: Peter Psenak [mailto:[email protected]] > Sent: Thursday, June 3, 2021 3:28 PM > To: DECRAENE Bruno INNOV/NET <[email protected]>; [email protected] > Subject: Re: [Lsr] RFC 8919 clarification > > 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 > > > > > ______________________________________________________________________ > ___________________________________________________ > > > > Ce message et ses pieces jointes peuvent contenir des informations > confidentielles ou privilegiees et ne doivent donc > > pas etre diffuses, exploites ou copies sans autorisation. Si vous avez recu > > ce > message par erreur, veuillez le signaler > > a l'expediteur et le detruire ainsi que les pieces jointes. Les messages > electroniques etant susceptibles d'alteration, > > Orange decline toute responsabilite si ce message a ete altere, deforme ou > falsifie. Merci. > > > > This message and its attachments may contain confidential or privileged > information that may be protected by law; > > they should not be distributed, used or copied without authorisation. > > If you have received this email in error, please notify the sender and > > delete this > message and its attachments. > > As emails may be altered, Orange is not liable for messages that have been > modified, changed or falsified. > > Thank you. > > _________________________________________________________________________________________________________________________ Ce message et ses pieces jointes peuvent contenir des informations confidentielles ou privilegiees et ne doivent donc pas etre diffuses, exploites ou copies sans autorisation. Si vous avez recu ce message par erreur, veuillez le signaler a l'expediteur et le detruire ainsi que les pieces jointes. Les messages electroniques etant susceptibles d'alteration, Orange decline toute responsabilite si ce message a ete altere, deforme ou falsifie. Merci. This message and its attachments may contain confidential or privileged information that may be protected by law; they should not be distributed, used or copied without authorisation. If you have received this email in error, please notify the sender and delete this message and its attachments. As emails may be altered, Orange is not liable for messages that have been modified, changed or falsified. Thank you.
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