Hi, Replication trees built with replication segments do have per-tree state. However please consider the following:
While an SR network does not need per-path state for unicast, it does not mean that multicast must strictly follow the same. Any of the following could be used, depending on an operator’s choice. 1. Ingress Replication or BIER 2. Traditional PIM or mLDP/RSVP P2MP solutions that maintain per-tree state for efficient replication 3. Replication tree based on replication segments but signaled from controllers via PCEP/BGP/NETCONF/whatever 4. Other options that are in the discussion in PIM/BIER WGs (e.g., BIER-RBS, encoding sub-tree in SRH) #1 is actually independent of SR, yet it sticks to SR principle (of no per-tree state in network) perfectly. However, we also need non-IR/BIER solutions for SR networks. Nobody can reject #2 as a valid option. For the same reason, #3 is also valid and it is what this WGLC is about. #3 allows an SR operator to use controller-based calculation & signaling and move away from PIM/mLDP/RSVP – to me that goes very well with SR even though it still has per-tree state. #3 with MPLS data plane is identical to #2 in the data plane, though we’re introducing this new “replication segment” term to go with the big SR framework. It is also the only non-BIER, non-legacy solution for SR-MPLS data plane (so far). For #3 with SRv6 data plane, while in concept it is similar to #3 with MPLS (the FUNCT bits of an SRv6 SID are the equivalent of P2MP label), we do need the replication segment concept and corresponding endpoint behavior defined for SRv6. In short, this document introduces the replication segment concept and defines the corresponding SRv6 endpoint behavior. It provides the building block for replication trees in SR network that are not necessarily set up via traditional means, and it does not exclude other solutions. Thanks. Jeffrey Juniper Business Use Only From: spring <spring-boun...@ietf.org> On Behalf Of Aijun Wang Sent: Saturday, December 10, 2022 8:35 PM To: Robert Raszuk <rob...@raszuk.net> Cc: SPRING WG <spring@ietf.org>; spring-cha...@ietf.org; Huaimo Chen <huaimo.c...@futurewei.com> Subject: Re: [spring] WGLC for draft-ietf-spring-sr-replication-segment [External Email. Be cautious of content] Hi, Joel and Robert: I think we should clarify what’s kind of state is that we are talking first before making any assertions. What we should avoid in Segments Routing panoramic view is that we shouldn’t introduce the per-flow state within the network. Consider the different multicast services require different multicast trees, you need to store different “Replications Segments” for different multicast services. Isn’t this per-flow state? Based on the same principle, the Binding-SID introduces also some kind of per-flow state in the network——if every different flow needs to take different paths at the advertising node——In such case, you need to keep many or per-flow Binding-SID at the advertising node. It violates certainly the dogmas of segment routing. The other SIDs(or that defined in RFC8986)that you mentioned are the states about the action of the related segment value and they are not Path-related, we can omit them. In summary, the “Replication Segment SID” that introduced in this draft has the similar effects that the MPLS label derived from the various distribution protocol of multicast VPN solutions. Will you also call these MPLS states within the transit nodes as segment routing based? Aijun Wang China Telecom On Dec 11, 2022, at 08:02, Robert Raszuk <rob...@raszuk.net<mailto:rob...@raszuk.net>> wrote: Joel, Yes IMO your understanding is correct. That does also mean that anyone who is making assertions that the subject document is introducing per flow "state" is just wrong or simply does not understand SR dogmas. Cheers, Robert. On Sun, Dec 11, 2022 at 12:42 AM Joel Halpern <j...@joelhalpern.com<mailto:j...@joelhalpern.com>> wrote: Speaking personally, my understanding of the "stateless" aspect of SR does not match what this email seems to describe. SR is path stateless. There is no state related to specific paths across the network. Any SID may be used, if it has relevant meaning, in any path. Advertising routers have internal state about what they mean when the advertise SIDs. Transit rotuers have state about where to forward packets based on the current SID in the packet. Binding SIDs have stored state about what stack of labels replace the binding SID at the advertising router. All these forms of state are considered by the community, as far as I can tell, as acceptable and reasonable forms of state with SR. Personally, it seems to me that replication SIDs have much the same kinds of state, and therefore fit well in the SR architecture. Yours, Joel On 12/9/2022 11:53 AM, Huaimo Chen wrote: Hi Everyone, It seems that the core value of segment routing is stateless (in the core of a network). The document defines a new type of segment for Segment Routing [RFC8402], called Replication segment. Using Replication segment is not stateless. This is not consistent with the core value of segment routing. I oppose the progress of the document. Best Regards, Huaimo ________________________________ From: spring <spring-boun...@ietf.org><mailto:spring-boun...@ietf.org> on behalf of James Guichard <james.n.guich...@futurewei.com><mailto:james.n.guich...@futurewei.com> Sent: Monday, November 28, 2022 10:10 AM To: SPRING WG <spring@ietf.org><mailto:spring@ietf.org> Cc: spring-cha...@ietf.org<mailto:spring-cha...@ietf.org> <spring-cha...@ietf.org><mailto:spring-cha...@ietf.org> Subject: [spring] WGLC for draft-ietf-spring-sr-replication-segment Dear WG: This email starts a 2-week Working Group Last Call for https://datatracker.ietf.org/doc/draft-ietf-spring-sr-replication-segment/<https://urldefense.com/v3/__https:/nam11.safelinks.protection.outlook.com/?url=https*3A*2F*2Fdatatracker.ietf.org*2Fdoc*2Fdraft-ietf-spring-sr-replication-segment*2F&data=05*7C01*7Chuaimo.chen*40futurewei.com*7C385b4881095c41b2c27008dad152b258*7C0fee8ff2a3b240189c753a1d5591fedc*7C1*7C1*7C638052450396258660*7CUnknown*7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0*3D*7C2000*7C*7C*7C&sdata=Xc85avPl8dZMqGuCSXAA6f89OTvRfQfQ6MGa9NCQnBE*3D&reserved=0__;JSUlJSUlJSUlJSUlJSUlJSUlJSUlJQ!!NEt6yMaO-gk!Aap0ylLmZYJ1m1MjpemXu4Fz7a4wq8hOk2RxE7cl_MTy9LmWoS0sxaf9JZve052OYvuoksWxsH1wBIomHPupKiGX$> Please read the updated document if you haven’t already and send your comments to the SPRING WG list no later than December 12th 2022. If you are raising a point which you expect will be specifically debated on the mailing list, consider using a specific email/thread for this point. Lastly, if you are an author or contributor please respond to indicate whether you know of any undisclosed IPR related to this document. Thanks! Jim, Joel & Bruno _______________________________________________ spring mailing list spring@ietf.org<mailto:spring@ietf.org> https://www.ietf.org/mailman/listinfo/spring<https://urldefense.com/v3/__https:/www.ietf.org/mailman/listinfo/spring__;!!NEt6yMaO-gk!Aap0ylLmZYJ1m1MjpemXu4Fz7a4wq8hOk2RxE7cl_MTy9LmWoS0sxaf9JZve052OYvuoksWxsH1wBIomHJ7SA_l8$> _______________________________________________ spring mailing list spring@ietf.org<mailto:spring@ietf.org> https://www.ietf.org/mailman/listinfo/spring<https://urldefense.com/v3/__https:/www.ietf.org/mailman/listinfo/spring__;!!NEt6yMaO-gk!Aap0ylLmZYJ1m1MjpemXu4Fz7a4wq8hOk2RxE7cl_MTy9LmWoS0sxaf9JZve052OYvuoksWxsH1wBIomHJ7SA_l8$> _______________________________________________ spring mailing list spring@ietf.org<mailto:spring@ietf.org> https://www.ietf.org/mailman/listinfo/spring
_______________________________________________ spring mailing list spring@ietf.org https://www.ietf.org/mailman/listinfo/spring
