Re: [mpls] [PWE3] ELI as a reserved label
John E Drake <jdrake@juniper.net> Tue, 03 August 2010 01:53 UTC
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From: John E Drake <jdrake@juniper.net>
To: "curtis@occnc.com" <curtis@occnc.com>
Date: Mon, 02 Aug 2010 18:49:43 -0700
Thread-Topic: [PWE3] [mpls] ELI as a reserved label
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Subject: Re: [mpls] [PWE3] ELI as a reserved label
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Curtis, What you are doing is speculating that our EL solution could be morphed to solve a problem for which the requirements are ill-defined. You refuse to understand that ELI is required in only a few cases and we do not want to make it mandatory. Have you actually read the I-D or are you simply assuming that it mirrors your pre-conceived notions? John Sent from my iPhone On Aug 2, 2010, at 8:39 PM, "Curtis Villamizar" <curtis@occnc.com> wrote: > > In message <16F10124-A08E-4532-8042-D7C290855CC6@juniper.net> > John E Drake writes: >> >> Hi, >> >> I think there is a misunderstanding. EL support is loosely coupled >> between the ingress and egress and intermediate nodes have no >> knowledge of its usage. Further, the ELI is normally *not* present. >> The normal mode of operation is for the egress to see a label for >> which it is expecting to see BOS set. The fact that it isn't tells >> the egress that an EL is present. > > John, > > You are jumping in without understanding the context of the > discussion. > > If stack depth used for hash is purposely limited for the purpose of > supporting a client MPLS-TP within an MPLS LSP, then the ELI and the > EL allow the label carrying entropy to be moved up the stack to where > it would be visible to the hash. > > For example, if an MPLS LSP carried one MPLS-TP LSP and one very large > IP/MPLS LSP, the forwarding label could be followed by ELI and then > EL. If the hash is limited to two, then MPLS-TP is unaffected. If > the midpoint LSR do not know the value of ELI being used, they cannot > look past it at the third label in the stack. > > This could also be solved by the ingress padding all LSP not using ELI > (by signaling an additional LSP that does nothing) but that is a very > ugly solution. > >> ELI is for IPv4/6 forwarding where there is no label in which to >> check >> for BOS not being set. Effectively, the ELI becomes that label. > > That was the original use, to avoid looking past BOS at the first > nibble. Keeping that behaviour (looking past BOS) solves the > multipath with MPLS-TP case since the hash is not label stack based, > as long as MPLS-TP always uses a control word. That is too limitiing > as MPLS-TP may also want to carry IP. > >> This renders any transit router usage of an ELI with a reserved value >> moot since most of the time it won't be there. >> >> Wrt p2mp, we cannot add either an EL or a reserved value ELI unless >> *all* receivers have indicated that they can receive it. > > Yes we all agree on that. > >> Thanks, >> >> John > > btw- The length of messages that you send from a phone never ceases to > amaze me. > > Curtis > >> Sent from my iPhone >> >> On Aug 2, 2010, at 10:18 AM, "Curtis Villamizar" <curtis@occnc.com> >> wrote: >> >>> >>> In message <8B7721F4-8C12-4C88-9036-B19592BE686E@castlepoint.net> >>> Shane Amante writes: >>>> >>>> Hi Curtis, >>>> >>>> I had some time to think about this some more on the plane ride >>>> home. >>>> See below. >>>> >>>> On Jul 30, 2010, at 14:02 GMT+02:00, Curtis Villamizar wrote: >>>>> In message <0DEFA7EF-8DC4-4EF2-ABDF-0404FC32B992@castlepoint.net> >>>>> Shane Amante writes: >>>>>> >>>>>> Curtis, >>>>>> >>>>>> On Jul 30, 2010, at 11:06 GMT+02:00, Curtis Villamizar wrote: >>>>>>> The Entropy Label Indicator (ELI) is called for in >>>>>>> draft-kompella-mpls-entropy-label-01.txt >>>>>>> >>>>>>> After brief discussion with Stewart and with Kireeti and Lucy >>>>>>> Yong, >>>>>>> there were three uses of ELI that would benefit from making the >>>>>>> ELI a >>>>>>> reserved label. It may be premature to make any such request >>>>>>> and the >>>>>>> remaining reserved label number space is sparse, so this will be >>>>>>> floated as a separate draft, and put on hold awaiting >>>>>>> advancement of >>>>>>> the drafts that depend on it. >>>>>>> >>>>>>> The three benefits of making ELI a reserved label are in: >>>>>>> >>>>>>> 1. Extending any use of entropy-label to P2MP (where there are >>>>>>> multiple egress and the possibility of each egress requiring a >>>>>>> separate entropy label value is problematic for the ingress). >>>>>>> >>>>>>> 2. Extending any use of entropy-label to any arbitrary position >>>>>>> in >>>>>>> the label stack such that in an aggregation LSP with >>>>>>> aggregates >>>>>>> both MPLS-TP and MPLS LSP, load split on the MPLS LSPs is >>>>>>> simplified and not impacted by limiting label stack depth for >>>>>>> the MPLS-TP LSPs. This is when label stack hash is limited to >>>>>>> support MPLS-TP as proposed in >>>>>>> draft-villamizar-mpls-tp-multipath-00.txt . >>>>>> >>>>>> I agree there are benefits to a reserved label for the above two >>>>>> applications. Most importantly, a receiving node would have >>>>>> pretty >>>>>> clearly semantics that what [immediately] follows a reserved >>>>>> ELI is >>>>>> the entropy-label, regardless of where the ELI is in the MPLS >>>>>> label >>>>>> stack and without needing to be in the signaling path to know >>>>>> what is >>>>>> the ELI value. >>>>> >>>>> "Now don't be sad ... 'cause two out of three aint bad". >>>>> [meatloaf] >>>>> >>>>> Its good to hear that you consider these to be useful. >>>>> >>>>> Note that an ingress LSR still needs to determine that egress LSR >>>>> understands ELI to do anything. To support MPLS-TP in MPLS the >>>>> ingress needs to veryify that all LSR on the path support MPLS >>>>> in a >>>>> way that provides a compliant path for a contained TP LSP, but >>>>> that is >>>>> out of scope of this discussion. >>>> >>>> I need to revise my statements wrt entropy-labels and P2MP LSP's. >>>> After thinking about this some more, I no longer believe it makes >>>> sense to use a reserved ELI value for P2MP LSP's. More >>>> specifically, >>>> for a given P2MP LSP, all receivers /MUST/ agree to receive entropy >>>> labels, because it would be silly to (for example) expect core >>>> LSR's >>>> to strip-off the ELI and an entropy-label mid-flight toward >>>> receivers >>>> that don't understand (or, can't receive) entropy-labels. The >>>> ramifications of this are that if a head-end detects any >>>> receivers of >>>> a P2MP LSP that can't receive entropy-labels, then the head-end >>>> LER/LSR must either: a) re-signal the whole P2MP LSP toward all >>>> receivers so that the head-end will not send any entropy-labels at >>>> all >>>> on the P2MP LSP; or, b) signal 2 separate P2MP LSP's: one for >>>> entropy-label capable receivers and a second for non-entropy-label >>>> capable receivers. I don't know that we want to mandate one of >>>> those >>>> two behaviors over the other, because SP's may make separate >>>> choices >>>> depending on whether they want to avoid extra replication in the >>>> network at the expense of not being able to do flow-based >>>> load-balancing, i.e.: Option (a), or don't mind the extra >>>> replication >>>> of (potentially) 2 parallel P2MP trees on the same links in order >>>> to >>>> attain some amount of flow-based load-balancing of the P2MP >>>> traffic. >>> >>> The use of a reserved label doesn't remove the requirement to figure >>> out if the egress can support ELI. It just removes the >>> requirement to >>> put a separate ELI label on for each egress. >>> >>> If some P2MP paths don't need to load balance (no multipath on that >>> leg) but other paths do, as long as all egress can support ELI, then >>> at worst it is 8 bytes of overhead that some paths don't need. >>> >>> I don't see an alternative for P2MP in your paragraph above. Are >>> the >>> branch points assumed to selectively add a different ELI (or none) >>> and >>> should branch point remove ELI and the entropy label if ELI is not >>> needed downstream or to the next branch point? Would this be a lot >>> more complicated with different values of ELI per egress (and >>> possibly >>> also per branch point)? >>> >>>> So, in summary, I no longer see that draft-kompella-mpls-entropy- >>>> label >>>> has a requirement for reserved labels for either P2P or P2MP LSP's >>>> (scenario 1 in your original e-mail). Furthermore, I still >>>> maintain >>>> that discussion of LFC and use of the MPLS TC field for >>>> indication of >>>> large vs. small flows is orthogonal to >>>> draft-kompella-mpls-entropy-label (scenario 3 in your original >>>> e-mail). I haven't read draft-villamizar-mpls-tp-multipath-00 >>>> (scenario 2 in your original e-mail) so I can't speak to whether or >>>> not there is a requirement for a reserved label there. >>> >>> OK. >>> >>>> Anyway, perhaps this will save you some time in that you don't need >>>> to >>>> write a whole new draft as you originally proposed and, instead, >>>> may >>>> only need to look at modifying your original draft. :-) >>> >>> For load balance to work with stack limited, then all midpoints >>> would >>> need to know what ELI was being used. >>> >>> This is a bit like each P2MP needing to know which ELI is needed >>> downstream of it, but not quite as bad. >>> >>> OTOH, putting the ELI that is being used on a P2P LSP in the PATH or >>> RESV message for that P2P LSP would solve this for "Use of Multipath >>> with MPLS-TP and MPLS" aka draft-villamizar-mpls-tp-multipath-00. I >>> could reference draft-kompella-mpls-entropy-label and make the >>> request >>> that you put the ELI label in the PATH or RESV message somewhere. >>> >>>> On a separate note, we intend to update >>>> draft-kompella-mpls-entropy-label shortly to cover P2MP LSP's >>>> (RSVP & >>>> mLDP), plus add details surrounding labelled BGP and RSVP P2P LSP's >>>> so >>>> that we have a more thorough treatment of all use cases to >>>> hopefully >>>> make all of this more clear. (In fact, I got a good start on this >>>> text on this on the plane ride home :-). >>> >>> OK. Just try to get the ELI into the PATH or RESV so all LSR on the >>> PATH can see it. >>> >>> BTW - There are some implications for facilities FRR. On the >>> facilities backup path there is no per LSP PATH or RESV message to >>> look at to see what value of ELI is being used. If the facilities >>> backup path is over multipath (ie: LAG, bundle, or RSVP ECMP), then >>> the value of ELI will not be known. This might force detour style >>> FRR >>> or use of GMPLS path protection (or segemenbt which is more >>> detour-like). A fixed ELI would help here too (allowing bypass >>> FRR). >>> >>>> -shane >>> >>> Maybe we should continue offline and then go back to the list. >>> >>> Curtis
- Re: [mpls] [PWE3] ELI as a reserved label Shane Amante
- Re: [mpls] ELI as a reserved label Shane Amante
- Re: [mpls] [PWE3] ELI as a reserved label Curtis Villamizar
- [mpls] ELI as a reserved label Curtis Villamizar
- Re: [mpls] [PWE3] ELI as a reserved label Shane Amante
- Re: [mpls] [PWE3] ELI as a reserved label Curtis Villamizar
- Re: [mpls] [PWE3] ELI as a reserved label Curtis Villamizar
- Re: [mpls] [PWE3] ELI as a reserved label Greg Mirsky
- Re: [mpls] [PWE3] ELI as a reserved label John E Drake
- Re: [mpls] [PWE3] ELI as a reserved label Curtis Villamizar
- Re: [mpls] [PWE3] ELI as a reserved label Curtis Villamizar
- Re: [mpls] [PWE3] ELI as a reserved label John E Drake
- Re: [mpls] [PWE3] ELI as a reserved label Curtis Villamizar
- Re: [mpls] [PWE3] ELI as a reserved label John E Drake
- Re: [mpls] [PWE3] ELI as a reserved label Curtis Villamizar
- Re: [mpls] [PWE3] ELI as a reserved label Yong Lucy
- Re: [mpls] [PWE3] ELI as a reserved label David Allan I
- Re: [mpls] [PWE3] ELI as a reserved label John E Drake
- [mpls] ELI and EL in P2MP (Re: [PWE3] ELI as a re… Curtis Villamizar
- Re: [mpls] [PWE3] ELI as a reserved label Curtis Villamizar
- Re: [mpls] ELI and EL in P2MP (Re: [PWE3] ELI as … Curtis Villamizar
- Re: [mpls] ELI and EL in P2MP (Re: [PWE3] ELI as … David Allan I
- Re: [mpls] [PWE3] ELI as a reserved label Kireeti Kompella
- Re: [mpls] [PWE3] ELI as a reserved label Kireeti Kompella
- Re: [mpls] [PWE3] ELI as a reserved label Curtis Villamizar
- Re: [mpls] [PWE3] ELI as a reserved label Yong Lucy
- Re: [mpls] [PWE3] ELI as a reserved label John E Drake
- Re: [mpls] [PWE3] ELI as a reserved label John E Drake
- Re: [mpls] [PWE3] ELI as a reserved label Yong Lucy
- [mpls] draft-ietf-mpls-entropy-label-01 Sami Boutros