Les, Use of context label for SR has been proposed 3 years back ..
https://tools.ietf.org/html/draft-raszuk-mpls-domain-wide-labels-05 I keep the draft, but I am about to drop it if there is no further interest. It beats me that group of folks went with such protocol pollution recommending use of indexes where no one I spoke with looking at SR deployment is not planning to have any use for it. As you may have noticed use of indexes even complicates your draft :) - - - Speaking of which how are you going to decide on which algorithm is to be chosen in section 3.2 ? I have similar observation as Stephane that it is very confusing at this point to provide many different ways in the document which is going to go for RFC. It is clearly not going to be easy to see a "rough consensus" - that can be used to gather forum feedback to progress the doc or not .. but I think it will rather be hard to judge as far as algorithm selection. Or are you going to run doodle ? Cheers, Robert. On Tue, Jul 5, 2016 at 6:54 PM, Les Ginsberg (ginsberg) <[email protected]> wrote: > Robert – > > > > Use of RFC 5331 would require that we have a way to advertise the context > label associated with a prefix-SID advertisement (whether in prefix > reachability or SRMS). This capability does not currently exist. > > > > So I believe my answer is correct based on existing definition of SR-MPLS > support. > > > > I am also not aware that RFC 5331 has been proposed as a generic solution > to RFC 5120 style MT even outside of SR – and likely for the same reason – > because there is no existing mechanism for advertising the context labels > associated with a prefix/MT pair. > > > > Les > > > > > > *From:* [email protected] [mailto:[email protected]] *On Behalf Of *Robert > Raszuk > *Sent:* Tuesday, July 05, 2016 12:30 AM > *To:* Les Ginsberg (ginsberg) > *Cc:* [email protected]; [email protected] > *Subject:* Re: [spring] draft-ietf-spring-conflict-resolution > > > > Hi Les, > > > > > However, this is not existing MPLS forwarding behavior and since SR > > > explicitly utilizes the existing MPLS forwarding behavior we not propose > > > any extensions. > > > > I am afraid the above assertion is not correct. Existing MPLS forwarding > already > > for a long time uses context-labels to set required topology for > forwarding. > > > > https://tools.ietf.org/html/rfc5331 > > > > Thx, > > R. > > > > > > On Tue, Jul 5, 2016 at 9:19 AM, Les Ginsberg (ginsberg) < > [email protected]> wrote: > > Bruno – > > > > SR-MPLS utilizes existing MPLS forwarding behavior without change. In this > model, the received label serves as the forwarding instruction for the > packet. This means that if two packets are received for the same > destination but we want the packet to follow two different forwarding > “topologies”, then we need to have two different labels. > > > > One can imagine a different model, where the forwarding instruction is > derived from the label AND some other attribute of the packet – and the > latter could be used to select a forwarding topology. However, this is not > existing MPLS forwarding behavior and since SR explicitly utilizes the > existing MPLS forwarding behavior we not propose any extensions. > > > > This is why different SIDs are required for the same destination in > different topologies. > > > > Les > > > > > > *From:* [email protected] [mailto:[email protected]] > *Sent:* Monday, July 04, 2016 5:07 AM > > > *To:* Les Ginsberg (ginsberg) > *Cc:* [email protected] > *Subject:* RE: draft-ietf-spring-conflict-resolution > > > > Les, > > > > Please see inline [Bruno3] > > > > *From:* Les Ginsberg (ginsberg) [mailto:[email protected] > <[email protected]>] > *Sent:* Friday, July 01, 2016 3:36 AM > *To:* DECRAENE Bruno IMT/OLN > *Cc:* [email protected] > *Subject:* RE: draft-ietf-spring-conflict-resolution > > > > Bruno – > > > > Inline. > > > > *From:* [email protected] [mailto:[email protected] > <[email protected]>] > *Sent:* Thursday, June 30, 2016 5:10 AM > *To:* Les Ginsberg (ginsberg) > *Cc:* [email protected] > *Subject:* RE: draft-ietf-spring-conflict-resolution > > > > Hi Les, > > > > Thanks for the discussion. Please see inline [Bruno] > > > > *From:* Les Ginsberg (ginsberg) [mailto:[email protected] > <[email protected]>] > *Sent:* Wednesday, June 29, 2016 6:19 PM > *To:* DECRAENE Bruno IMT/OLN > *Cc:* [email protected] > *Subject:* RE: draft-ietf-spring-conflict-resolution > > > > Bruno – > > > > > > *From:* [email protected] [mailto:[email protected] > <[email protected]>] > *Sent:* Wednesday, June 29, 2016 7:22 AM > *To:* Les Ginsberg (ginsberg) > *Cc:* [email protected] > *Subject:* RE: draft-ietf-spring-conflict-resolution > > > > Hi Les, > > > > IINM, I’ve not seen the follow up on one of my below questions. > > So let me restate a comment: > > > > The SR-MPLS SID conflicts algo requires that all nodes consider the same > mapping advertisements. > > How is this ensured, if it indifferently considers advertisements from all > protocols, while some nodes could participate only in a subset of the > protocols? e.g. OSPF only routers would consider a different set of > information compared to OSPF+IS-IS routers. > > > > *[Les:] If you run multiple protocol instances (whether multiple instances > of the same protocol or instances of different protocols) then you need to > insure that at least one of the two conditions below is true:* > > · All routers receive the equivalent set of advertisements > > · There are no conflicts J > > > > [Bruno] IOW, the draft does not resolve SID conflict if all routers do not > receive exactly the same set of advertisement from all routing protocols. > > That’s indeed can be a valid simplification if the WG choose to, but this > should clearly be indicated in the document, in a section targeting network > operator since this point will need to be read and enforced by network > operator rather than protocol implementors. §3.2.8 already partly address > this, but IMO a text clearly expressing the requirements on network > operator would be useful. > > > > *[Les2:] No policy can guarantee consistent results network wide if the > databases on different nodes are inconsistent. This isn’t a > “simplification” – it is a fact. As you point out, Section 3.2.8 already > states:* > > > > *“In order to obtain consistent active entries all nodes in a network* > > * MUST have the same mapping entry database.”* > > > > *If you believe this is not explicit enough please suggest some text.* > > [Bruno3] > > Section 4 Manageability Considerations > > Detecting and resolving conflicts in a consistent way requires that all > nodes consider the same set of SIDs advertisements. Network operations > should be aware that the conflict resolution algorithm defined in this > document will not succeed in selecting a consistent resolution across all > nodes, if all nodes do not receive the exact same set of SIDs > advertisements. This may be in particular the case when multiple IGP > instances are used and all routers do not participate in the same set of > IGP instances. This may occurs for example if one network transition from > one IGP protocol to another IGP (e.g. from OSPFv2 to IS-IS). This may also > happen if IGP areas/level are used and SIDs are not flooded in all > areas/levels. > > > > > > *One way of insuring the first point is to exclusively use a mapping > server to advertise SIDs, configure your SRMS entries in a protocol > independent manner, and insure that the SRMS advertisements are sent in all > of the protocol instance specific sub-domains.* > > [Bruno] IOW, don’t make configuration errors ;-) > > Are you implying that the SRMS configuration (hence yang model) should be > per node rather than per protocol? or at least should be configurable by > node (and possibly also by protocols) > > > > *[Les2:] My point is (humorous ideas aside…) that if a deployment uses > multiple protocols, the easiest way to guarantee that the SID mapping > database on all nodes in the network is consistent is to restrict SID > advertisements to SRMS advertisements.* > > [Bruno3] Clearly, the fewer the number of advertisements for a given > prefix, the less change of conflict. > > But I fail to see why only using SRMS guarantee anything. e.g. if > different nodes use a different set of routing protocols, you have > conflicts. Idem if the misconfiguration consist in adding a SID to a IGP > prefix (PFX advertisement) > > > > > > *A small number of nodes (as few as 1 – more if redundancy is desired) are > setup as mapping servers and all SIDs which are required network-wide are > configured on these nodes and advertised by the protocol instance(s) on > that node. In this way it is not necessary to guarantee that all prefix > reachability from all of the protocol instances running in the network are > present in all the protocol instance sub-domains which exist – it is only > necessary to insure that all protocol instances advertise the same set of > SRMS entries.* > > [Bruno3] In the end, this gets back to requiring no configuration mistakes. > > *It isn’t the only way to support this – but it is likely to be the > simplest and least error prone. In any case this isn’t a requirement – it > was a response to your question as to how it might be possible to get > consistent SID mapping databases on all nodes in such a case. This is no > way changes how the YANG model is defined. SRMS config is always node > specific.* > > > > > > *If the intent is to deliberately use different labels in the forwarding > plane for the same destination depending upon which protocol advertised the > prefix, this introduces a number of new requirements – not the least of > which is duplicate entries for the same prefix in the forwarding plane. As > has been discussed publicly in a different thread, there are cases (e.g. > merging two networks) were such a requirement may exist – but it is the > exception rather than the rule and as it consumes more resources in the > forwarding plane and introduces implementation complexity independent of > conflict resolution it is not the primary case the draft focuses on. > Nevertheless, this is a case which the draft will address in the next > revision.* > > [Bruno]There is also the point of configuring different SRGB space in > different IGP protocols. In which case, SIDs may conflict but this is not > an issue as label will not conflict. > > *We stopped short of that in this revision because we felt there were > enough substantive changes and points on which consensus is still a work in > progress that it would not be the optimal way forward.* > > [Bruno] +1 and thanks. Releasing an updated version has been useful to > re-initiate the discussion. > > > > Thinking more about this, I guess that this is only important for the > entries which are inserted in the forwarding plane. Hence, in case of > conflict between protocols, I think that the preference algorithm should > take into account the protocol preference (aka administrative distance). > > > > *[Les:] As admin distance is neither an attribute of SRMS entries nor > guaranteed to be consistent on all routers for all prefixes this is not a > desirable approach. * > > [Bruno] Well, the some prefix/routing consistency is also required for IP > prefixes. When then same IP prefix is advertised in different IGPs, admin > distance is a common existing way to define which routing protocol takes > precedence. I’m not sure why it should not also be taken into consideration > for SR Prefix conflits > > > > *[Les2:] Please see my response to Stephane on the same point.* > > > > I’m also not sure to see why is the problem different compared to > Multi-Topology. Could you please elaborate? > > *[Les:] I am unclear what your question is. Are you asking why we need > different SIDs in different topologies? Please clarify.* > > [Bruno] Question was that, at a very/too high level, the issue of conflict > across topology seems close to the issue of conflict across routing > protocols: we have different topologies. Hence a naïve question: how > exactly is this different. > > One part of the answer, is the simplification proposed when multiple > protocols is used (i.e. your first answer above). > > Another part is that for multi-topology, compared to multi-protocols, all > information from all topologies are flooded to all nodes. > > Another part is the forwarding model used for Multi-Topology. In general, > https://tools.ietf.org/html/rfc5120#section-8 seems to assume that each > topology has one dedicated RIB/FIB. In such condition, there is no conflict > (prefix or SID) so no need to detect and resolve conflict. So here there > may be different models and eventually, we don’t ‘have the same one in mind. > > In a lesser extend, even for multi-protocols, we may have those multiple > forwarding models. To some extent, this seems related to the definition of > “SR domain”. e.g. if we have 2 IGPs, do we have 1 or 2 SR domains? May be > this is something that needs to be configurable > > > > > > *[Les2:] Please reread Section 3.1.2. While there are no > “Prefix-conflicts” across topologies, there are “SID Conflicts”. This is > important to understand.* > > [Bruno3] Conflicts are related to a forwarding context i.e. FIB. This is > equally important to understand. Please read > https://tools.ietf.org/html/rfc5120#section-8.2.2 and 8.2.1 to see that > topologies may not share the same forwarding context hence do not conflict > in term of prefix & SID. > > --Bruno > > > > *As regards multiple protocols operating in the same topology, from a > forwarding perspective we do not care what protocol is the winning route. > What we care about is that our nexthop has chosen the same SID for a given > prefix. This is why “source” is deliberately excluded from consideration by > the conflict resolution algorithm.* > > > > * Les* > > > > * Les* > > > > > > Thanks, > > Bruno > > > > *From:* spring [mailto:[email protected] <[email protected]>] *On > Behalf Of *[email protected] > *Sent:* Wednesday, May 18, 2016 1:57 PM > *To:* Les Ginsberg (ginsberg); [email protected] > *Subject:* Re: [spring] draft-ietf-spring-conflict-resolution > > > > Les, > > > > Thanks for your reply. > > Please see inline [Bruno] > > > > *From:* Les Ginsberg (ginsberg) [mailto:[email protected] > <[email protected]>] > *Sent:* Saturday, May 14, 2016 8:30 PM > *To:* DECRAENE Bruno IMT/OLN; [email protected] > *Subject:* RE: draft-ietf-spring-conflict-resolution > > > > Bruno – > > > > Inline. > > > > *From:* spring [mailto:[email protected] <[email protected]>] *On > Behalf Of *[email protected] > *Sent:* Thursday, May 12, 2016 8:23 AM > *To:* [email protected] > *Subject:* [spring] draft-ietf-spring-conflict-resolution > > > > Hi, > > > > As an individual contributor, please find below some comments: > > > > -- > > Isn’t this document specific to the MPLS dataplane? > > If so, it could be indicated in the introduction, and possibly in the > abstract. Then this indication could be removed from the 1rst sentence of > sections 2 & 3. > > > > *[Les:] Currently all discussion is regarding SR-MPLS. The draft leaves > open the possibility that if there is some SRv6 conflict resolution that > needs to be specified it could be added into this document – which is why > the Introduction is dataplane agnostic, but each section states > specifically that it is relevant to SR-MPLS.* > > > > *I am not aware of any SRv6 conflict resolution that is required at this > point, but I prefer to leave the possibility open if that is OK with you.* > > [Bruno] ok, great. > > -- > > §3 > > “Mapping entries have an explicit context which includes the topology and > the SR algorithm.“ > > A priori you could add “the routing protocol”. > > > > *[Les:] No – the source of advertisements is deliberately left out. It > matters not whether the source of the advertisement is a protocol or an > SRMS – nor does it matter which protocol provides the advertisement. You > see that “admin distance” is not mentioned at all and that is quite > deliberate. This insures that consistent choices are made on nodes > regardless of which protocol might have the best route on a given node.* > > [Bruno] Well, the fact is that mapping entries do have, as explicit > context, the routing protocol used to advertise them. After, you can should > to use that information, or not. > > -- > > §3 > > “When conflicts occur, it is not > > possible for routers to know which of the conflicting advertisements > > is "correct". If a router chooses to use one of the conflicting > > entries forwarding loops and/or blackholes may result unless it can > > be guaranteed that all other routers in the network make the same > > choice. Making the same choice requires that all routers have > > identical sets of advertisements and that they all use the same > > selection algorithm. » > > > > I think we agree on the technical part, but I found the formulation slightly > biased. I would propose > > “When conflicts occur, it is not > > possible for routers to know which of the conflicting advertisements > > is "correct". In order to avoid forwarding loops and/or blackholes, there > is a need for all nodes to make the same choice. > > Making the same choice requires that all routers have > > identical sets of advertisements and that they all use the same > > selection algorithm. This is the purpose of this document. » > > -- > > *[Les:] I am fine with this change.* > > [Bruno] Thanks > > > > §3.1 > > “Various types of conflicts may occur” > > What about :s/Various/Two > > > > *[Les:] “Two” is fine. Just means we will have to change it if we come up > with a third type of conflict. **J* > > [Bruno] Indeed, but in this case the change may be much larger (e.g. the > whole algo) > > -- > > I agree with Robert’s and Uma’s comment with regards to making this > conflict resolution an inter- protocol/routing_table issue. In particular, > between SR domains, there is not requirement to have unique SIDs. Hence > between PE and CE, between ASes (both within and across organization), the > same SID could be reused independently). > > > > *[Les:] There is more to be said on this topic – co-authors are actively > discussing this point and we’ll respond more fully to Robert’s post in > time. But, the draft is NOT trying to define conflict resolution across “SR > domains”. Perhaps we need language to make that more explicit.* > > [Bruno] ok. Regarding inter-protocol, in order to have consistency of the > prefix-SID mapping across the domain we need: > > a) all nodes use the same algo > > b) all nodes using this algo have the same data > > > > “a” requires this draft > > “b” requires that all nodes have the same set of SR info. This forbid > that some node are considering IS-IS + OSPF SR data, while some node are > only considering IS-IS data. Otherwise, all IS-IS routers would not take > the same decision. So, unless we can guarantee that the flooding area is > the same for IS-IS and OSPF, we can't have the algo using the SR data from > multiple routing protocols. I don't think that we can guarantee this (nor > that implementation will check this) e.g. when some nodes are part of > multiple routing domain or when gradually transitioning from one IGP to > another. > > > > So in short, this SR-conflict algo should probably be restricted to SR > information from a single protocol > > > > > From: Les Ginsberg (ginsberg) [mailto:[email protected] > <[email protected]>] > Sent: Sunday, May 01, 2016 7:11 AM > > > > > > We are indeed defining conflict resolution across all the SID > advertisements regardless of source (protocol or SRMS) > > > Why? Because we need consistent use of SIDs in the forwarding plane > > > > No: in the forwarding plane, we need a consistent use of MPLS label. > > *[Les:] As you know, SRGB range can be different for different nodes, so > the actual label that is used to send a packet for a given destination via > Node A may be different than the label used to send the same packet via > Node B. It is the SID that needs to be the same – not the label. * > > *It is true that SIDs are not installed in the forwarding plane – the > labels derived from the SID/SRGB are what is actually installed in the > forwarding plane – but I think my use of the word SID in this context is > correct.* > > [Bruno] My point was that the formulation assumes that a single SRGB is > used per nodes. In which case, we have a bijection between SID and labels. > But if we have a SRGB per protocol, we don’t have a bijection any more and > we can have the same SID in IS-IS and OSPF (including for different > prefix), which will be mapped to different labels in the forwarding plane. > > > > Plus only within an SR domain. Actually, even within a domain, this is > dependent on whether SRGB is configured on a per node or a per protocol > basis. I’m not sure how much the agreement has been reached on that one. > > > > *[Les:] The draft currently addresses deployments where a single (set of) > SRGB ranges applies to the box. This is by far the most common use case. > There is a much more limited use case where protocol specific SRGBs and > protocol specific SIDs may be required. The draft will address that in a > future revision* > > [Bruno] ok, may be this should be stated in the draft, as otherwise you’ll > keep getting comments, or we may forget this point. > > Thanks > > --Bruno > > *– but in spirit the same rules will apply – they will just have to take > into account “duplicate forwarding domains”. Note that this will also > require multiple incoming label entries/prefix be supported by the routers > in such a network.* > > > > -- > > Typo: > > §2 > > OLD : Range 3: (500, 5990 > > NEW : Range 3: (500, 599) > > > > (somewhat significant as otherwise range 3 conflict with range 2) > > > > *[Les:] Agreed – thanx for spotting this.* > > > > *Les* > > > > 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. 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