Bruno -
First, thank you very much for the time you have invested in thinking about the issues and writing alternative text for the draft. I can appreciate that this took significant time - and your input will certainly help us move forward. I want to reemphasize the goals that hopefully we all share. This is best illustrated in Slide #9 from my presentation at IETF94: https://www.ietf.org/proceedings/94/slides/slides-94-spring-2.pdf [cid:[email protected]] Detection, reporting, and consistent handling are the points of emphasis. What is deliberately deemphasized is the choice of resolution behavior. This is done because of the points made in Slide #8: [cid:[email protected]] We could evaluate every possible solution and how it behaves in all of the possible misconfigurations. But I think this will take a very long time(years...) and give us very little return on the time spent. Indeed, over a year has already been spent in private/semi-private/public discussions on this topic and at the time the draft was written we were no closer to achieving consensus than when we started. My goal is to have a version with broad consensus ready for WG adoption by IETF95. To achieve that we need input from more folks than you - hopefully your hard work will encourage others to contribute. But we also need a commitment to the priorities outlined in the slides reproduced above. To the extent that your contributions help to clarify the options we have it is very valuable work and I again express my gratitude to you for providing this input. But if we spend the next few months trying to complete definition of all of the possible options and how they behave in a variety of potential misconfigurations I believe we will not be able to meet the goal. In response to your post I am going to start two different threads: 1)SRGB Inconsistency 2)SID Conflict Resolution. I want to separate these two topics because I think they do not have a logical relationship - and because I am hopeful that we will be able to achieve consensus easily on SRGB inconsistency. :) This will then allow us to spend more cycles on SID Conflict resolution where I think the bulk of the remaining discussion is likely to occur. Please look for the two new threads in the next day or two. Les > -----Original Message----- > From: [email protected] [mailto:[email protected]] > Sent: Thursday, December 17, 2015 9:27 AM > To: [email protected]; Les Ginsberg (ginsberg) > Subject: draft-ginsberg-spring-conflict-resolution > > Hi Les, authors, WG > > As an individual contributor, please find below some more detailed > comments and considerations on the draft. > > Following the "please send text" request expressed during the meeting, > please find enclosed some proposed text. (xml, txt, diff versus public > version). > > I wished I had sent this before, but writing the text took longer than > expected. BTW I still not happy with my text, but hopefully current text (or > at least the table of content) should be enough to give an idea on the > direction I have in mind. > > Thanks, > Regards, > Bruno > > __ > As previous expressed on the mailing list and during the meeting, I'm > especially concerned with Mapping Server advertisement where a single > typo/bug can conflict with many/all SIDs in the network. In this case, I don't > think that dropping all traffic to those SIDs is a desirable option. > One option is to prefer individual advertisement (prefix SID) over general > ones (Mapping Server). i.e. more specific wins. Note that this is the approach > currently taken by the IS-IS draft: > " For a given prefix, if both a MS entry with its Prefix-SID Sub-TLV > and a Prefix TLV (e.g.: TLV135) with its Prefix-SID are received, the > Prefix-SID advertised within the Prefix TLV MUST be preferred while > the MS entry MUST be ignored." > > We can probably assume that this is already implemented (by compliant > implementations), so I'm not sure to see the value of changing existing > implementations if this is to get a more disruptive result for the network. > __ > Regarding SID conflict, the current draft proposes to drop all conflicting > information. > Looking at the big picture, this means: the more (Mapping Server) > redundancy, the more risk of conflict, the less availability. > This is probably not the property that we are looking for. > __ > > I support the comment to consider the error handling work "recently" done > in the IDR WG. IMHO, WG and authors did a good work on such a difficult > subject (just like for SID conflicts, at the beginning opinions were diverse, > and everyone had good reasons). > I'm not sure how much reading the end result (RFC 7606) helps in > understanding all the trade-off considered during the work. Reading the > operational requirements, given that the IGP infrastructure is probably even > more important than BGP for network operators/clients/traffic, it may be > worthwhile to read BGP error handling operation requirements ( > https://tools.ietf.org/html/draft-ietf-grow-ops-reqs-for-bgp-error-handling-<https://tools.ietf.org/html/draft-ietf-grow-ops-reqs-for-bgp-error-handling-07> > 07<https://tools.ietf.org/html/draft-ietf-grow-ops-reqs-for-bgp-error-handling-07> > ) Discussion with the people involved may help. FYI, as for me, the point I > learnt are: > - when we detect an error on the receiving side, there is a bug. In general, > it's > difficult to know whether the bug is on the sending side or the receiving > side. > Clearly, for the receiving side, the first reaction is to blame the sending > side. > For each error, it's useful to consider both options (i.e. error may be on > my/receiving side). And even if the error is on the sending side, the receiver > may run the same implementation (so "sender is too buggy to live" may > apply to your own implementation i.e. the receiving side). > - when we detect an error, it's useful to consider all possible causes and > consequences before deciding to make things worse (e.g. killing a > session/transit node/prefix). In particular, there may not be a single error > but > many (SIDs, source routers (especially if the error is on the receiving > side)). > So it's useful to consider that the decision may be multiplied 10 or 100 > times. > > Clearly there are difference between IGP & BGP: usually more redundancy in > BGP (more signaling path (redundant RR) and more AS exit points), more > prefixes hence the cost of dropping one prefix is relatively less important, > two-way point to point signaling channel, messages are flooded unchanged > so people are less likely to shoot the messenger and errors are less likely to > be multiplied during propagation.... > > __ > "An > alternative is to ensure at the nodes which originate these > advertisements that no such overlap is allowed to be configured. > Such overlaps can then be considered as a conflict if they are > received. This allows a simpler and more efficient implementation of > the database. This is the approach assumed in this document." > > I encourage implementation to check the configurations before accepting it. > And to check its routing advertisement before sending it. I would assume > that state of the art implementation will do it. Yet, I don't think it should > be > considered as an excuse to avoid error handling at the protocol level. > BTW, I'm not sure how much you expect implementation checks to be done > before committing/sending. e.g. If an operator configure a range on the > SRMS, and this ranges conflict with existing SID advertised by other nodes, > would you expect the implementation to detect such conflict and reject the > configuration? > More generally, if we assume some extensive checks by implementations > before committing/sending, and that given such assumption we define a > light error handling, I'd like such assumptions be documented in the > document and probably be made normative (since the receiving side, is > expected a specific behavior from the sending side, this is normative). > Also "implementation of the database" is implementation dependent and is > probably just one aspect of the implementation simplicity/efficiency. > And speaking for myself, simplicity/efficiency/availability of 100s networks > running segment routing significantly out weight the "simplicity and > efficiency" of one to ten implementations. > > __ > "The occurrence of conflicts is > easily diagnosed from the behavior of the network as the forwarding > of traffic which would, in the absence of conflicts, utilize > segments no longer does so." > > I don't think that we need to kill customer's traffic to raise awareness of > the > network operator. And I don't support the idea that the more traffic you kill, > the easier and faster the error is resolved. > If you need to raise an error, please do so! e.g. in logs, syslogs, SNMP > traps, > netconf event notification... Dropping the traffic is not providing more > information, it is increasing the pressure and hence the probability of quick > erroneous actions. Not to mention that as all services will run over packet > networks, and as there is a pressure to reduce costs we may have a single > converged network for all services. In this case, there is a chance that if > the > network is down, some people/tools/equipment may not be reached > anymore/easily. e.g. calling people on their cell phone does not work when > the packet network is down. > > __ > " The downside of ignoring conflicting entries is that forwarding of > all packets with destinations covered by the conflicting entries will > always be negatively impacted." > > Let's call a spade a spade. (btw, I prefer the French version :s/spade/cat > which nowadays should be more popular on the Internet ;-) ) The traffic is > not "negatively impacted", the traffic is "dropped". And for all > services/customers/BGP routes using theses SIDs. > > __ > 3.2.2. Preference Algorithm > [...] > "This approach requires that conflicting entries first be identified" > > All approach requires conflicting entries to be identified. This is not a > drawback of the "preference algorithm" > > "Based on which entry is preferred this in turn may impact what other > entries are considered in conflict" > > This is not additional rule/work. This is applying the same rule/algo to > subsequent entries. > Also, from the network perspective, in the end, this will not drop more > entries than the "ignore rule", quite the contrary. > > "Based on > which entry is preferred this in turn may impact what other entries > are considered in conflict i.e. if A conflicts with B and B > conflicts with C - it is possible that A does NOT conflict with C. > Hence if as a result of the evaluation of the conflict between A and > B, entry B is not used the conflict between B and C will not be > considered." > > I'm not sure to get what is implied. As A and B conflicts and B and C > conflicts, > with "ignore conflicting entries", I would assume that all A, B, C be ignored, > no? Or do you plan to ignore conflicting entries until there is no conflict? > In > which case we would only remove one of the two conflicting entries and end > up with a "preference" resolution 'and never drop both conflicting entries > since once we drop the first, there is no more conflict) ___ > > > > __________________________________________________________ > __________________________________________________________ > _____ > > 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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