Hi all, As a network operator, please see my 2cents inline [Bruno]
> From: Ahmed Bashandy (bashandy) > Sent: Tuesday, November 10, 2015 1:54 AM > > Thanks a lot Les for the elaborate explanation > > One small addition to what Les mentioned. The functionality proposed by > the draft can be achieved by having a base prefix-SID index and then > configuring an offset (instead of an SRGB) for each topology/algorithm > pair from that base prefix-SID index value. Based on the configured > offset, the router would then calculate the corresponding prefix-SID > index for each topology/algorithm pair and advertise it using existing > mechanisms [Bruno] This is correct. However, IMO this is a drawback to have: a) the network operator configure a specific value (offset) attached to a specific item (algo/topology) b) the protocol (and hence the logs/show/dumps...) advertise a different value (SID+offset) attached to a different item (prefix) I fear that this would not help the troubleshooting, in particular in difficult situations (e.g. significant network issue, with significant pressure and possibly with non-expert people involved. e.g. "I know why this does not work: the offset configured is not advertised" or "The SID advertised does not match the configured one" ...) So I don't feel that the "offset" proposal is fully equivalent. Thanks -- Bruno > Note that the above is NOT a suggestion to use the offset mechanism to > configure prefix-SID indices. The objective is to show that the draft > does not offer enough benefits to warrant all the questions marks that > are outlined in Les's email. > > Thanks > > Ahmed > > On 11/9/2015 1:11 AM, Les Ginsberg (ginsberg) wrote: > > Chris - > > > > I have a number of questions - but in order to properly frame them I need > to recount some history - please bear with me. > > > > In the very early days of SR there was a proposal to reserve a fixed label > range on all routers (16000 - 23999) for the use of SR. This seemed workable > but there was concern that the same range would not be available on all > routers so the SR community agreed that we needed to allow the > advertisement of a different SRGB range on each SR capable router. > > > > Then, another concern was raised that a single contiguous range large > enough to meet the SR requirements might not be available on all routers and > therefore we needed to support the advertisement of multiple SRGB ranges > from a given node. This capability has been added - though it has also raised > other concerns regarding how many ranges might be enough and how to deal > with inconsistencies (overlaps) in the advertised ranges should some error > occur. > > > > Now, in support of multiple algorithms/topologies, this draft proposes that > algorithm/topology specific SRGBs be advertised - and that to fully get the > benefits of consistent SID assignment for the same prefix across > algorithms/topologies (the major goal of this draft) that all routers be able > to > support identical ranges for each algorithm/topology. (Section 5 goes into > this > in detail) - and to be able to allocate new ranges for newly configured > algorithms/topologies on demand. Section 6 goes on to suggest that it would > be a wonderful goal if all routers could assign the same base label/range to > each algorithm/topology so that the labels could be derived algorithmically > (though you admit this may not always be possible). > > > > My first question is how do you reconcile this requirement for consistency > on all nodes with the earlier decisions to support inconsistency as regards > SRGB base values/range sizes? > > > > My second question is associated with the assumption of a single > "node_index" per node. I for one would be delighted if we could get > agreement on using a single host address/node (or at least one per AF) for all > traffic to that node. But this does not meet the deployment requirements in > all cases and so we support multiple "node_indeces" for a given node. This > means that we do not map SIDs to nodes - we map SIDs to prefixes. So it is > conceptually more straightforward and less problematic to configure SIDs for > prefix ranges. This is in fact how SRMS advertisements are constructed i.e. > > > > (Prefix/Prefix length, Starting SID, Range) > > > > How would you propose to incorporate this style of SID assignment into your > algorithms? Do you assume a maximum number of node-sids required for > every node in the network and require the range for each algorithm/topology > be sized large enough for the worst case? This seems potentially wasteful - > especially if a deployment chooses to use a particular address for a topology > as a traffic differentiator. > > > > My third question relates to the algorithm/topology independence of the > SID assignment that you propose. Throughout the document you assume that > you have a single SID for a given prefix and you simply add the appropriate > algorithm/topology specific SRGB base value to this SID to derive the > forwarding label. However, current protocol advertisements for SIDs include > both algorithm and topology as context for the SID. This reflects the current > SR architecture which has been defined with algorithm/topology as an explicit > context for a SID. Your proposal fundamentally changes this and therefore all > existing encodings of SID advertisements (prefix reachability, SRGB, SRMS > advertisements) would have to be changed in a non-backwards compatible > way in order to support your proposal. Other than definition of a new SRGB > advertisement, you do not discuss this in the draft. How do you intend to > address this major issue? > > > > Les > > > > > >> -----Original Message----- > >> From: spring [mailto:[email protected]] On Behalf Of Chris Bowers > >> Sent: Monday, October 05, 2015 12:31 PM > >> To: [email protected] > >> Subject: [spring] FW: New Version Notification for draft-bowers-spring- > adv- > >> per-algorithm-label-blocks-02.txt > >> > >> SPRING WG, > >> > >> There was quite a lot of discussion in person after we presented draft- > >> bowers-spring-adv-per-algorithm-label-blocks-01 in Prague, and there was > >> also much discussion on this list about the issue raised by this draft. We > have > >> made two main additions to this revision of the draft to further this > >> discussion. > >> > >> 1) We have included discussion of multiple topologies in addition to > multiple > >> algorithms, and we have modified the proposed ISIS extension to handle > >> both multiple topologies and multiple algorithms. > >> > >> 2) We have tried to accurately describe a proposal, which was outlined on > >> this list, for managing the assignment of per-topology/per-algorithm node > >> index values, which we refer to as the "configured offset mapping > method". > >> > >> We welcome feedback from the working group on this draft. > >> > >> Thanks, > >> Chris > >> > >> -----Original Message----- > >> From: [email protected] [mailto:[email protected]] > >> Sent: Monday, October 05, 2015 2:05 PM > >> To: Uma Chunduri <[email protected]>; Hannes Gredler > >> <[email protected]>; Pushpasis Sarkar <[email protected]>; Chris > >> Bowers <[email protected]>; Chris Bowers <[email protected]>; > >> Uma Chunduri <[email protected]>; Pushpasis Sarkar > >> <[email protected]>; Hannes Gredler <[email protected]> > >> Subject: New Version Notification for draft-bowers-spring-adv-per- > >> algorithm-label-blocks-02.txt > >> > >> > >> A new version of I-D, draft-bowers-spring-adv-per-algorithm-label-blocks- > >> 02.txt > >> has been successfully submitted by Chris Bowers and posted to the IETF > >> repository. > >> > >> Name: draft-bowers-spring-adv-per-algorithm-label-blocks > >> Revision: 02 > >> Title: Advertising Per-Topology and Per-Algorithm Label > Blocks > >> Document date: 2015-10-05 > >> Group: Individual Submission > >> Pages: 14 > >> URL: > >> https://www.ietf.org/internet-drafts/draft-bowers-spring-adv- > >> per-algorithm-label-blocks-02.txt > >> Status: > >> https://datatracker.ietf.org/doc/draft-bowers-spring-adv-per- > >> algorithm-label-blocks/ > >> Htmlized: https://tools.ietf.org/html/draft-bowers-spring-adv-per- > >> algorithm-label-blocks-02 > >> Diff: > >> https://www.ietf.org/rfcdiff?url2=draft-bowers-spring-adv-per- > >> algorithm-label-blocks-02 > >> > >> Abstract: > >> When segment routing is used in a network that is controlled by a > >> link state IGP (such as ISIS or OSPF), each node in the network can > >> be assigned one or more index numbers, known as "node-SIDs". The > >> node-SIDs are unique within the network, and are known to all the > >> nodes in the network. If an ingress node has a data packet to be > >> sent to an egress node, the ingress node may select a node-SID > >> corresponding to the egress node, and "translate" that node-SID to an > >> MPLS label. The MPLS label represents a particular path to the > >> egress node; the path is determined by applying a routing algorithm > >> to a particular view of the network topology and a particular set of > >> metric assignments to the links of that topology. The packet can > >> then be forwarded by pushing the label on the packet's label stack > >> and transmitting the packet to the next hop on the corresponding path > >> to the egress node. This document compares two different procedures > >> for translating a node-SID to the MPLS label that represents a path > >> chosen by a particular algorithm operating on a particular topology. > >> It also specifies the ISIS extensions needed to support one of the > >> procedures (known as the "per-topology/per-algorithm label block" > >> procedure). > >> > >> > >> > >> > >> Please note that it may take a couple of minutes from the time of > submission > >> until the htmlized version and diff are available at tools.ietf.org. > >> > >> The IETF Secretariat > >> > >> _______________________________________________ > >> spring mailing list > >> [email protected] > >> https://www.ietf.org/mailman/listinfo/spring > > _______________________________________________ > > spring mailing list > > [email protected] > > https://www.ietf.org/mailman/listinfo/spring > > > _______________________________________________ > spring mailing list > [email protected] > https://www.ietf.org/mailman/listinfo/spring _________________________________________________________________________________________________________________________ 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. 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