Re: [Idr] draft-ietf-idr-next-hop-capability
Aijun Wang <wangaijun@tsinghua.org.cn> Fri, 16 September 2022 15:10 UTC
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Date: Fri, 16 Sep 2022 23:10:20 +0800
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Cc: idr@ietf.org, Gyan Mishra <hayabusagsm@gmail.com>, draft-ietf-idr-next-hop-capability@ietf.org, draft-scudder-idr-entropy-label@ietf.org
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To: bruno.decraene@orange.com
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Subject: Re: [Idr] draft-ietf-idr-next-hop-capability
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Hi, Bruno: No. Let the “BGP Next-hop dependent Capabilities Attributes” transitive is more reasonable. There is also another drawback of your bellowing proposal: how to encode the RLD value? Keep still the current “Entropy Label Next-Hop dependent Capabilities” in your document? Then there will be two places to encode the same information. Aijun Wang China Telecom > On Sep 16, 2022, at 21:45, bruno.decraene@orange.com wrote: > > > Of-list, I’ve been told that some form of backward compatibility with a deployed software (namely ELCv2, minus the squatted code-point) is a significant aspect for some actors. > > I think that there may be a path to account for both the past history (ELCv2) and the future generic capabilities (BGP Next-Hop Capability) with the following attribute encoding: > -Transitive BGP attribute, code point TBD. > - Capability encoding : > > +---------------------------------------------------------+ > | Address Family Identifier (2 octets) | > +---------------------------------------------------------+ > | Subsequent Address Family Identifier (1 octet) | > +---------------------------------------------------------+ > | Length of Next Hop Network Address (1 octet) | > +---------------------------------------------------------+ > | Network Address of Next Hop (variable) | > +---------------------------------------------------------+ > > Followed by an optional set of NH Capabilities encoded as > +------------------------------+ > | Capability Code (2 octets) | > +------------------------------+ > | Capability Length (2 octets) | > +------------------------------+ > | Capability Value (variable) | > ~ ~ > +------------------------------+ > > > That way: > - Existing implementations see the same content as ELCv2/v3. All they need is to accept and ignore trailing octets > - Other BGP Next-Hop capabilities may be encoded as BGP Next-Hop capability code and allowing capability value. > > The main drawback that I can see is that if, in a distant future, one implementation would need to advertise some BGP Next-Hop Capabilities but without advertise ELC, we would need to define a BGP Next-Hop capability code to signal the non-support of ELC (negative capability announcement). > However, given the existing history (ELCv2), that may be seen as a reasonable way to merge both approaches into a single solution, with minimal impact for existing implementations (accept trailing octets, use a different codepoint). > > Hope this helps, > Regards, > Bruno > > > > > > > From: DECRAENE Bruno INNOV/NET > Sent: Friday, September 16, 2022 2:11 PM > To: idr@ietf.org; 'Gyan Mishra' <hayabusagsm@gmail.com> > Subject: draft-ietf-idr-next-hop-capability > > Dear WG, Gyan > > draft-ietf-idr-next-hop-capability provides the ability to advertise BGP Next-Hop dependent capabilities. This is typically useful for advertising data plane related capabilities. > The draft also defines a first BGP Next-Hop capability to advertise the Entropy Label Capability. As such the draft updates RFC6790. > > For this, the draft defines a new non-transitive BGP Attribute. > The use of a non-transitive attribute (vs a transitive attribute) has benefits and disadvantages, more specifically with regards to legacy implementations not supporting draft-ietf-idr-next-hop-capability. > > - the benefit of using a non-transitive attribute is that the attribute is automatically removed by implementation not supporting draft-ietf-idr-next-hop-capability, with no extra complexity (logic, data, code and related tests/bugs) as RFC 4271 already provides the non-transitivity. > - the cost of using a non-transitive attribute is that a BGP node which is both 1) propagating the BGP route while not in the data plane path (not changing the BGP Next-Hop) and 2) not supporting draft-ietf-idr-next-hop-capability will remove the attributes/Next-Hop capabilities even though it would not need to as the BGP Next-Hop (hence the Next-Hop capabilities) is unchanged. So essentially the benefit is for BGP Route Reflectors which do not support yet draft-ietf-idr-next-hop-capability. The benefit is likely to be transient and for a small portion of the nodes (e.g. 1%) however it’s definitely real and helps for incremental deployments. > > I have two questions for the WG: > - is the above pro & con analysis complete or are there points that would need to be added or removed ? > - given the pro & con, does the WG prefer the use of a non-transitive or a transitive capability? > > > Note that moving to a transitive attribute would require to add extra logic/code and extra data in the attribute (both being described in draft-scudder-idr-entropy-label) and in short: > - the extra data: capability Next-Hop (AFI, SAFI, length of Next-Hop field, Next-Hop address) > - the extra logic: if Next-Hop address is different in the attribute and in the BGP Next-Hop, then disregard and remove the attribute. > The editor and authors of draft-scudder would be welcome to join as co-authors. (To be transparent, the chairs and AD would likely impose a 5 or 6 authors limit) > > 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. > _______________________________________________ > Idr mailing list > Idr@ietf.org > https://www.ietf.org/mailman/listinfo/idr
- [Idr] draft-ietf-idr-next-hop-capability bruno.decraene
- Re: [Idr] draft-ietf-idr-next-hop-capability bruno.decraene
- Re: [Idr] draft-ietf-idr-next-hop-capability Aijun Wang
- Re: [Idr] draft-ietf-idr-next-hop-capability bruno.decraene
- Re: [Idr] draft-ietf-idr-next-hop-capability Aijun Wang
- Re: [Idr] draft-ietf-idr-next-hop-capability bruno.decraene