Hi I do not quite get the same warm and fuzzy from the definition when thinking about multicast…..
The mapping of the binding SID to local policy is still IMO per path state. For a simple p2p path it is pretty straightforward as the mapping can be to a common policy abstraction at every node (send to ‘x’) . In the case of multicast, the mapping would be unique at every node that had state for the binding SID (send copy to ‘a’ and ‘b’, send copy to ‘m’ and ‘q’ etc.) . So some means of disseminating the mappings is required, and correlating them with the SID. So the difference between a binding SID and a global SID for multicast IMO is choice of terminology. So you have to decide if the whole “avoiding per path state” discussion is simply a desirable goal, or a strict admonition. A bulk overprovisioning model to eliminate per path state will not work for multicast. Cheers Dave From: spring <spring-boun...@ietf.org> On Behalf Of Alexander Vainshtein Sent: Tuesday, June 19, 2018 6:38 AM To: bruno.decra...@orange.com; Stewart Bryant <stewart.bry...@gmail.com> Cc: SPRING WG List <spring@ietf.org>; Rob Shakir <robjs=40google....@dmarc.ietf.org> Subject: Re: [spring] Updating the SPRING WG Charter Bruno, Stewart and all, I have looked up Section 5 “Binding Segment” of the Segment Routing Architecture<https://tools.ietf.org/html/draft-ietf-spring-segment-routing-15> draft, and it says: In order to provide greater scalability, network opacity, and service independence, SR utilizes a Binding SID (BSID). The BSID is bound to an SR policy, instantiation of which may involve a list of SIDs. Any packets received with active segment = BSID are steered onto the bound SR Policy. A BSID may either be a local or a global SID. If local, a BSID SHOULD be allocated from the SRLB. If global, a BSID MUST be allocated from the SRGB. Use of a BSID allows the instantiation of the policy (the SID list) to be stored only on the node(s) which need to impose the policy. Direction of traffic to a node supporting the policy then only requires imposition of the BSID. If the policy changes, this also means that only the nodes imposing the policy need to be updated. Users of the policy are not impacted. From my POV this definition is fully aligned both with the Bruno’s last email and with my earlier argument why a BSID does not add a per-path state in the transit nodes. Regards, Sasha Office: +972-39266302 Cell: +972-549266302 Email: alexander.vainsht...@ecitele.com<mailto:alexander.vainsht...@ecitele.com> From: spring [mailto:spring-boun...@ietf.org] On Behalf Of bruno.decra...@orange.com<mailto:bruno.decra...@orange.com> Sent: Tuesday, June 19, 2018 3:38 PM To: Stewart Bryant <stewart.bry...@gmail.com<mailto:stewart.bry...@gmail.com>> Cc: SPRING WG List <spring@ietf.org<mailto:spring@ietf.org>>; Rob Shakir <robjs=40google....@dmarc.ietf.org<mailto:robjs=40google....@dmarc.ietf.org>> Subject: Re: [spring] Updating the SPRING WG Charter Hi Stewart, Speaking as individual contributor, please see inline [Bruno] From: spring [mailto:spring-boun...@ietf.org] On Behalf Of Stewart Bryant Sent: Tuesday, June 19, 2018 1:19 PM On 01/06/2018 17:05, Rob Shakir wrote: The SPRING WG defines procedures that allow a node to steer a packet through an SR Policy instantiated as an ordered list of instructions called segments and without the need for per-path state information to be held at transit nodes. I am not sure where the line gets drawn with the per-path state statement. If I introduce a binding-SID to allow the creation of a path, have I introduced per-path state or not? In practise a management entity will choose between the infinity of possible binding-SIDs by considering the need to create specific paths and I would imagine that many will be instantiated just-in-time. I think that the key point is that the ingress creates the path by using SIDs to create a concatenation of paths, policies and resources. [Bruno] Agreed. And it can be argued that this creates a state on the ingress. An “outgoing” state, very roughly comparable to Next Hop Label Forwarding Entry (NHLFE)) However it could be argued that as soon as we introduced Binding SIDs we introduced per-path state. [Bruno] Adding a Binding SID to this SR policy introduces an “incoming” state, very roughly comparable to Incoming Label Map (ILM). But this gets additional benefit as it allows others SR nodes to use this state/SR policy. I’m not sure that in such high level text, we need to make such distinction. I think we might be best served by deleting the text I have highlighted. [Bruno] This text is mostly a copy/past from existing charter so is not really new: “allow a node to steer a packet along an explicit route using information attached to the packet and without the need for per-path state information to be held at transit nodes. ” At high level, I believe that this is a key distinction of spring/segment routing hence worth keeping in the high level introduction of the WG. Now do we need to add text about more specific details, such as BSID? I’d rather not, as I don’t see what this would bring. I also don’t think that this sentence prohibits the creation of states when required/useful. --Bruno - Stewart _________________________________________________________________________________________________________________________ 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. 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