Re: [OSPF] [Isis-wg] Mail regarding draft-ietf-ospf-segment-routing-extensions

<stephane.litkowski@orange.com> Mon, 12 January 2015 10:53 UTC

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From: stephane.litkowski@orange.com
To: "Henderickx, Wim (Wim)" <wim.henderickx@alcatel-lucent.com>, DECRAENE Bruno IMT/OLN <bruno.decraene@orange.com>, Rob Shakir <rjs@rob.sh>
Thread-Topic: [OSPF] [Isis-wg] Mail regarding draft-ietf-ospf-segment-routing-extensions
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Date: Mon, 12 Jan 2015 10:53:40 +0000
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Subject: Re: [OSPF] [Isis-wg] Mail regarding draft-ietf-ospf-segment-routing-extensions
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Very good point, in our case, today we have up to 15 strict hops for TE tunnels.
When we will introduce interdomain, it will bring more.

-----Original Message-----
From: Henderickx, Wim (Wim) [mailto:wim.henderickx@alcatel-lucent.com] 
Sent: Monday, January 12, 2015 11:45
To: LITKOWSKI Stephane SCE/IBNF; DECRAENE Bruno IMT/OLN; Rob Shakir
Cc: ospf@ietf.org; spring@ietf.org; draft-ietf-ospf-segment-routing-extensions@tools.ietf.org; isis-wg@ietf.org; draft-ietf-isis-segment-routing-extensions@tools.ietf.org
Subject: Re: [OSPF] [Isis-wg] Mail regarding draft-ietf-ospf-segment-routing-extensions

How many hops do we want to support in these scenario’s realistically?
This might help in determining the options

On 12/01/15 09:54, "stephane.litkowski@orange.com"
<stephane.litkowski@orange.com> wrote:

>Hi Bruno,
>
>Using TTL may work or not. Backup path does not mean that you will 
>defacto have more hops. Metric of backup path could be higher but 
>number of hops equal or smaller.
>
>I created a new thread on SPRING WG list to discuss the different options.
>
>Thanks !
>
>-----Original Message-----
>From: DECRAENE Bruno IMT/OLN
>Sent: Monday, January 12, 2015 09:49
>To: LITKOWSKI Stephane SCE/IBNF; Rob Shakir
>Cc: isis-wg@ietf.org;
>draft-ietf-ospf-segment-routing-extensions@tools.ietf.org; 
>ospf@ietf.org; 
>draft-ietf-isis-segment-routing-extensions@tools.ietf.org
>Subject: RE: [OSPF] [Isis-wg] Mail regarding 
>draft-ietf-ospf-segment-routing-extensions
>
>Hi,
>
>2 cents inlined
>
>> From: OSPF [mailto:ospf-bounces@ietf.org] On Behalf Of > 
>> stephane.litkowski@orange.com
>> 
>> Hi,
>> 
>> After discussing a lot with Les offline, we almost found an agreement 
>> on the understanding of this use case and possible relationship with 
>> unprotected SIDs.
>> Use case :
>> 	Creation of a SR TE tunnel which is unprotected. Protection may be 
>> provided end to end using for example two disjoint paths.
>> 	Controller based or ingress based tunnel setup.
>> 
>> It seems clear now that using ONLY unprotected SIDs does not solve 
>>the  issue as when a link fails, convergence will happen, and nodes 
>>that  are near the failure may reroute a NodeSID Algo 0 used within 
>>the TE  stack before Ingress or controller recomputes the new path 
>>fitting  constraints. So there may be transient situations where the 
>>path does not fit constraints anymore.
>> Based on this, introducing "NON PROTECTED" NodeSID does not help in  
>>solving this transient situation.
>> 
>> Now, as I explained, IMO, it's possible to introduce end to end OAM 
>> on top on the SRTE to bring the LSP down as soon as there s something 
>> wrong on the path. A Holddown timer can be used to keep LSP down 
>> until convergence happens at Ingress or Controller. But introducing 
>> such OAM and holddown and coupled with relations with IGP may also be 
>> complex and there is a chance that it does not solve the issue. In 
>> case of protected NodeSID used, OAM will not work, because switchover 
>> time will be too small. Using OAM , defacto requires path with no protection.
>> So unprotected SID+OAM may solve the use at the price of some 
>> complexity and possibly not solving 100% of the cases.
>> 
>> To conclude :
>> We need to solve this use case and we need to find another elegant, 
>> simple and scalable solution for this.
>> 
>> Possible existing solutions :
>> - Use Adj-SID only => does not sounds good as there will be an impact 
>> of stack depth => Path compression necessary
>> - Use binding TLV and create some new Node-SID corresponding to a set 
>> of Adj-SID => This introduces more states within the network (how 
>> many
>> ?)
>> - Anything else ?
>
>Combining Adj-SID and Node-SID with a very restricted TTL (to expire on 
>the backup path) may be able to avoid IGP rerouting of this LSP.
>
>/Bruno
>
> 
>> Best regards,
>> 
>> Stephane
>> 
>> 
>> -----Original Message-----
>> From: Rob Shakir [mailto:rjs@rob.sh]
>> Sent: Thursday, January 08, 2015 10:52
>> To: LITKOWSKI Stephane SCE/IBNF
>> Cc: Les Ginsberg (ginsberg); Shraddha Hegde; Pushpasis Sarkar; Peter 
>> Psenak (ppsenak); 
>> draft-ietf-ospf-segment-routing-extensions@tools.ietf.org;
>> draft-ietf-isis-segment-routing-extensions@tools.ietf.org; Hannes 
>> Gredler; ospf@ietf.org; isis-wg@ietf.org
>> Subject: Re: [Isis-wg] [OSPF] Mail regarding
>> draft-ietf-ospf-segment-routing- extensions
>> 
>> Stephane,
>> 
>> If we think about the “MUST NOT be protected” case that you mention.
>> Let’s assume that we have a service that is performance sensitive, 
>> such that we want to take a particular path through the network - and 
>> that we use Node- SIDs like you say.
>> 
>> If we assume that the requirement is for A-B-C-D-E path below. The 
>> node SID for E points via C-D-E and hence is used for stack 
>> compression like you
>> say:
>> 
>>       A -- B -- C -- D -- E
>>                 |        /
>>                 --- Q ---
>> 
>> In your envisaged behaviour, C does not protect the Node-SID for E. 
>> In the case of the C-D link failure, then the “preferred” behaviour 
>> is that C now drops traffic towards this destination. However, C does 
>> not remove the FIB entry for the Node-SID for E, it’s actually just 
>> now known via Q. At this point, A can forward with exactly the same 
>> stack, and the packet takes a new A-B- C-Q-E path, which is 
>> non-conformant with the performance requirement of the service.
>> 
>> In terms of what C does with its FIB, does it simply not use C-Q-E 
>> during the failure, but post-reconvergence use it anyway? If so, why 
>> not use C-Q-E during the failure - because the service is always 
>> going to non-conformant to the performance requirement?
>> 
>> With an Adj-SID, it makes sense, because essentially unless that 
>> adjacency is available, then there is no alternate path for the SID 
>> that will be taken - so traffic never hits a non-conformant path.
>> 
>> Practically, if I can’t tell a customer that the path taken will  
>>definitely be A-B- C-D-E, and it may rather go via C-Q-E at some point  
>>following convergence [until the head-end calculates that such a  
>>change had happened - either a link outage, or a metric change - and  
>>stops using the label stack], then there’s little problem of having 
>>the traffic go via C-Q-E during protection.
>> 
>> For the disjoint case, the consideration that one has to make is:
>> 	* are alternative SPF paths for a particular Node-SID actually still  
>>conformant with the disjointness requirement? How many simultaneous  
>>failures does one require to violate constraints. For example, in a  
>>dual-plane core network, then if the requirement is disjointness at  
>>the IP level, then we may need to lose connectivity entirely within  
>>the plane before it is preferable to “hop” to another plane. In this  
>>case, using an alternative SPF path for the Node-SID is actually not a 
>>problem for disjointness.
>> 	* does the application prefer losing an entire path to having some  
>>risk of the services being shared fate until the re-optimisation?
>> 
>> From the work that we’ve looked at thus far, I have not yet seen a 
>> case where I absolutely MUST NOT use an alternate shortest path for a 
>> Node-SID and hence don’t require protection at a practical level.
>> 
>> Stack depth is definitely going to be something that we need to  
>>consider - to me, where we have centralised controller - actions such  
>>as dynamically created forwarding-adjacency LSPs which allow  
>>“expansion” of one segment into a set of segments within the path are  
>>attractive as a solution where one needs to have explicit routing of 
>>traffic for TE purposes.
>> 
>> Does this make sense, or do you see the use case that we’re 
>> addressing here differently?
>> 
>> Cheers,
>> r.
>> 
>> 
>> > On 7 Jan 2015, at 09:44, stephane.litkowski@orange.com wrote:
>> >
>> > Hi,
>> >
>> > I'm coming into this long thread and I tried to read all the 
>> > exchange but I may be missed some lines :)
>> >
>> > But here is my opinion on this subject.
>> > I think the point from Shradda is valuable in case of Traffic 
>> > Engineering with
>> Segment Routing, especially with a central controller.
>> >
>> > Today in TE networks, we are selling some disjoints paths to 
>> > customer that
>> MUST NOT be protected (SDH like services). It would be good to 
>> reproduce the same thing with SR-TE.
>> >
>> > Now, current encoding permits to advertise that a specific Adj-SID 
>> > is
>> protected or not (as already mentioned, this does not say that a 
>> protection really exists ..., in case of LFA protection , there may 
>> be no FRR path for this adj-SID despite of the protection flag set).
>> > We pretty know that it would not be possible in all case to use 
>> > only Adj-SID
>> for a TE tunnel (due to label stack depth), so we need to introduce 
>> stack compression using SPT segments and node-SID.
>> > So to reply on Rob's comment, on RSVP-TE tunnels with looses hops 
>> > that
>> does not request protection : yes for RSVP, it does not make sense to 
>> me, but for SR, due to stack compression, it will be needed.
>> >
>> > If we look at a network, where TE is managed by a central 
>> > controller, how
>> the controller can ensure that the node-SID used is protected or not 
>> (as for Adj-SID, I mean protection requested, not protection 
>> installed). I see two ways :
>> > 	* Use two SIDs attached to the same prefix and add a flag to 
>> > prevent
>> automatically all nodes to compute a protection for one of the SID.
>> The flag does not really force nodes to compute a protection. Each  
>>node will still require local configuration for protection, but the  
>>flag will permit to exclude some prefixes for protection (overriding 
>>local policy).
>> >
>> > 	* Use two prefixes on each node , prefixes are marked with tags
>> (admin-tags) : "protection tag" and "non protection tag". Each router  
>>is configured using LFA policies to not compute protection for  
>>prefixes having "non protection tag" AND add knowledge to the  
>>controller to use only "non protection tag" prefixes to compress non 
>>protected path.
>> >
>> >
>> > Best Regards,
>> >
>> > Stephane
>> >
>> > -----Original Message-----
>> > From: Isis-wg [mailto:isis-wg-bounces@ietf.org] On Behalf Of Les 
>> > Ginsberg (ginsberg)
>> > Sent: Monday, January 05, 2015 16:59
>> > To: Shraddha Hegde; Pushpasis Sarkar; Peter Psenak (ppsenak); 
>> > draft-ietf-ospf-segment-routing-extensions@tools.ietf.org;
>> > draft-ietf-isis-segment-routing-extensions@tools.ietf.org; Hannes 
>> > Gredler
>> > Cc: ospf@ietf.org; isis-wg@ietf.org
>> > Subject: Re: [Isis-wg] [OSPF] Mail regarding 
>> > draft-ietf-ospf-segment-routing-extensions
>> >
>> > Shraddha -
>> >
>> > As Jeff has already mentioned, the case you are concerned about can 
>> > be handled using LFA selection strategies discussed in 
>> > http://datatracker.ietf.org/doc/draft-ietf-rtgwg-lfa-manageability/
>> > And it is a far better solution since it allows the traffic of 
>> > interest to be
>> protected => less traffic interruption.
>> >
>> >   Les
>> >
>> >
>> >
>> > -----Original Message-----
>> > From: Shraddha Hegde [mailto:shraddha@juniper.net]
>> > Sent: Monday, January 05, 2015 12:49 AM
>> > To: Les Ginsberg (ginsberg); Pushpasis Sarkar; Peter Psenak 
>> > (ppsenak); 
>> > draft-ietf-ospf-segment-routing-extensions@tools.ietf.org;
>> > draft-ietf-isis-segment-routing-extensions@tools.ietf.org; Hannes 
>> > Gredler
>> > Cc: ospf@ietf.org; isis-wg@ietf.org
>> > Subject: RE: [OSPF] [Isis-wg] Mail regarding 
>> > draft-ietf-ospf-segment-routing-extensions
>> >
>> > Les,
>> >
>> > Pls consider a case when the post convergence path goes through a
>> different node and is well provisioned.
>> >
>> > --------G-------
>> > |                     |
>> > A----B----C----D
>> >        |       |
>> >          E----F
>> >
>> > When the link between B & C goes down, we don’t want to divert the
>> traffic via B-E-E-F-C because it is not well provisioned for the 
>>service.
>> > The post convergence path is A-G-D which is well provisioned.
>> > In this case it makes sense to simply avoid protection for the 
>> > service as the
>> nature of the service is such that it can be disconnected and 
>> reconnected without impacting the end user of the service.
>> >
>> >
>> > The post convergence paths need to be provisioned at least for one 
>> > failure
>> if that is not the case then the service will remain down 
>> Irrespective of the technology used.
>> >
>> >
>> > Rgds
>> > Shraddha
>> >
>> > -----Original Message-----
>> > From: Les Ginsberg (ginsberg) [mailto:ginsberg@cisco.com]
>> > Sent: Monday, January 05, 2015 12:07 PM
>> > To: Pushpasis Sarkar; Shraddha Hegde; Peter Psenak (ppsenak); 
>> > draft-ietf-ospf-segment-routing-extensions@tools.ietf.org;
>> > draft-ietf-isis-segment-routing-extensions@tools.ietf.org; Hannes 
>> > Gredler
>> > Cc: ospf@ietf.org; isis-wg@ietf.org
>> > Subject: RE: [OSPF] [Isis-wg] Mail regarding 
>> > draft-ietf-ospf-segment-routing-extensions
>> >
>> > Pushpasis -
>> >
>> > Inline.
>> >
>> > -----Original Message-----
>> > From: Pushpasis Sarkar [mailto:psarkar@juniper.net]
>> > Sent: Sunday, January 04, 2015 10:13 PM
>> > To: Les Ginsberg (ginsberg); Shraddha Hegde; Peter Psenak 
>> > (ppsenak); 
>> > draft-ietf-ospf-segment-routing-extensions@tools.ietf.org;
>> > draft-ietf-isis-segment-routing-extensions@tools.ietf.org; Hannes 
>> > Gredler
>> > Cc: ospf@ietf.org; isis-wg@ietf.org
>> > Subject: Re: [OSPF] [Isis-wg] Mail regarding 
>> > draft-ietf-ospf-segment-routing-extensions
>> >
>> > Hi Les,
>> >
>> >
>> > On 1/5/15, 11:23 AM, "Les Ginsberg (ginsberg)" <ginsberg@cisco.com>
>> wrote:
>> >
>> >> Pushpasis -
>> >>
>> >> The key point is that the proposal does not have any lasting 
>> >> impact on traffic flow. A simple topology should suffice to illustrate this.
>> >>
>> >>
>> >> A----B----C----D
>> >>         |       |
>> >>         E----F
>> >>
>> >> (All links have the same cost)
>> >>
>> >> Suppose we wish to have traffic entering at A flow along the path 
>> >> A-B-C-D
>> >> - but if the link B---C fails we do NOT want traffic to take the 
>> >> path B--E--F--C.
>> >>
>> >> You propose to have C advertise an address with two node-sids - 
>> >> one which allows protection - call it C(P) - and one which does 
>> >> NOT allow protection - call it C(NP).
>> > [Pushpasis] No. My proposal is for D to advertise two node sids, D1 
>> > with NP
>> set to 0 and D2 with NP set to 1. Applications on that do not need B, 
>> or C to protect the A-B-C-D path will use D2. B and C will not 
>> install backup paths for D2. Other apps can use D1 as they are 
>> supposed to do otherwise. Wether to protect D1 or not is a local decision of B and C.
>> > Hope I could clarify enough :)
>> >
>> > [Les:] Whether we talk about C or D doesn’t matter. As you point 
>> > out
>> below the issue you are concerned with is the FIB update time on the 
>> intermediate nodes relative to the recomputation on the ingress node.
>> >
>> >>
>> >> If the label stack specifies C(NP) - then while the link B--C is 
>> >> UP everything works as desired (primary path to C(NP) on Node B is 
>> >> via link B-C).
>> >> However, when the link B--C goes down, the network will reconverge 
>> >> and in a modest amount of time the new primary path to C(NP) on 
>> >> node B will be via link B-E.
>> > [Pushpasis] Yes agreed. But only applications on A will be 
>> > injecting traffic
>> using D2. Once the B-C link-down event reaches router A will stop  
>>injecting traffic using D2. A path re-compute will be triggered on A.
>> Yes I agree that if B converges D2 (not FRR) before A re-compute,  
>>there is still chance that some small amount of traffic is sent over 
>>A-B-E-F-C-D.
>> >
>> > [Les:] Well yes - the key point is that you cannot guarantee the 
>> > timing of
>> when B (for example) will reconverge relative to when the ingress 
>>node  A decides to reroute/drop the D2 traffic. Given that B is closer 
>>to  the failure it is quite likely that B will respond more quickly 
>>than A
>> - and of course there are many other variables which could affect the  
>>relative response time of A and B. So the sole benefit of what you  
>>propose seems to be that in some cases you MIGHT not send as much 
>>traffic to D2 via the undesired links.
>> >
>> > At this point I think you would do well to look at the existing 
>> > solutions - as
>> well as Jeff's post on this thread which provides an excellent 
>> framework for thinking about solutions. We do have ways of addressing 
>> this problem and doing so far more robustly than what you are 
>> proposing. The ROI for what you propose is quite low. For my part I 
>> don’t think what you propose is a good idea.
>> >
>> >    Les
>> >
>> >>
>> >> The existence of C(NP) therefore only affects traffic flow during 
>> >> the reconvergence period i.e. if we assume B did NOT install a 
>> >> repair path for C(NP) traffic will be dropped only until a new 
>> >> primary path is calculated. I don’t see the value in this.
>> >>
>> >> As a (somewhat dangerous) aside, the functionality you are looking 
>> >> for is more akin to "not-via" as defined in RFC 6981 - though I am 
>> >> quick to add that I am NOT proposing to pursue that. :-) But 
>> >> reading that RFC might give you more insight into why simply 
>> >> setting "don't protect" for a prefix isn't useful for the purpose
>>you have in mind.
>> >>
>> >>  Les
>> >>
>> >>
>> >>
>> >> -----Original Message-----
>> >> From: Pushpasis Sarkar [mailto:psarkar@juniper.net]
>> >> Sent: Sunday, January 04, 2015 8:34 PM
>> >> To: Les Ginsberg (ginsberg); Shraddha Hegde; Peter Psenak 
>> >> (ppsenak); 
>> >> draft-ietf-ospf-segment-routing-extensions@tools.ietf.org;
>> >> draft-ietf-isis-segment-routing-extensions@tools.ietf.org; Hannes 
>> >> Gredler
>> >> Cc: ospf@ietf.org; isis-wg@ietf.org
>> >> Subject: Re: [OSPF] [Isis-wg] Mail regarding 
>> >> draft-ietf-ospf-segment-routing-extensions
>> >>
>> >> Hi Les,
>> >>
>> >> Please find comments inline..
>> >>
>> >> Authors,
>> >>
>> >> Here is my proposal. Please let me know if this sounds reasonable 
>> >> or
>>not.
>> >>
>> >> - A new ŒNo-Potection-Required¹ or ŒNP¹ flag be added to the 
>> >> Prefix-SID Sub-TLV/TLV. Setting this flag means none of the 
>> >> transit routers should try to protect this node-segment.
>> >> - Let nodes advertise two node-sid-index each (per 
>> >> address-family), one without and one with ŒNP¹ flag set. For 
>> >> node-sid advertised with ŒNP¹ flag 0, routers same behave the same 
>> >> way as today. But when they receive a node-sid with ŒNP¹ flag set, 
>> >> they avoid/skip finding a backup for that segment.
>> >> - Finally ingress servers or TE-applications may use these 
>> >> 'node-sids with NP-flag set¹ for use cases where it is better to 
>> >> drop traffic on topology outages rather than diverting it to some 
>> >> other paths. For such cases ingress router or TE-applications 
>> >> should look for node-sids with ŒNP¹ flag set and not the regular 
>> >> node-sids. For all other normal use cases(including L3VPN/6VPE 
>> >> etc) traffic should be carried using node-sid without ŒNP‹flag set.
>> >>
>> >> Thanks and Regards,
>> >> -Pushpasis
>> >>
>> >> On 1/5/15, 3:37 AM, "Les Ginsberg (ginsberg)" <ginsberg@cisco.com>
>> wrote:
>> >>
>> >>> Pushpasis -
>> >>>
>> >>> I don't agree.
>> >>>
>> >>> The use of one node-sid vs another has nothing whatever to do 
>> >>> with the request Shraddha has made i.e. should we introduce a 
>> >>> flag indicating whether a particular prefix should be protected or not.
>> >>> A node-sid only dictates what (intermediate) node traffic should 
>> >>> be sent to - not what
>> >>> link(s) are used to reach that node.
>> >> [Pushpasis] This is not about which links to take. It is about 
>> >> wether transit routers should try to protect the node-segment to 
>> >> the this node-sid or not. I think this opens up a lot many number 
>> >> of possibilities on the ingress router and TE controller-based
>>applications.
>> >>
>> >>>
>> >>> Adjacency-sids have a different semantic - they identify the link 
>> >>> over which traffic is to be forwarded. Identifying an 
>> >>> adjacency-sid as unprotected means traffic will NEVER flow over a
>>different link.
>> >>> There is no equivalent behavior w a node-sid - which is what this 
>> >>> discussion has been about.
>> >> [Pushpasis] I am not trying to draw a parallel between this new 
>> >> flag and the ŒB¹ flag in Adj-Sid SubTlv. Like said before
>> >>
>> >>>
>> >>>  Les
>> >>>
>> >>>
>> >>> -----Original Message-----
>> >>> From: Pushpasis Sarkar [mailto:psarkar@juniper.net]
>> >>> Sent: Sunday, January 04, 2015 8:51 AM
>> >>> To: Les Ginsberg (ginsberg); Shraddha Hegde; Peter Psenak 
>> >>> (ppsenak); 
>> >>> draft-ietf-ospf-segment-routing-extensions@tools.ietf.org;
>> >>> draft-ietf-isis-segment-routing-extensions@tools.ietf.org
>> >>> Cc: ospf@ietf.org; isis-wg@ietf.org
>> >>> Subject: Re: [OSPF] [Isis-wg] Mail regarding 
>> >>> draft-ietf-ospf-segment-routing-extensions
>> >>>
>> >>> Hi Les,
>> >>>
>> >>> I think the requirement Shraddha is referring is about the choice 
>> >>> of exact node-sid to use while constructing the label-stack for a 
>> >>> explicit-LSP on the ingress router, which will be typically done 
>> >>> after running some CSPF on the SPRING topology. And not the IGP 
>> >>> on ingress or transit routers.
>> >>>
>> >>> Thanks
>> >>> -Pushpasis
>> >>>
>> >>> On 1/3/15, 3:10 AM, "Les Ginsberg (ginsberg)" 
>> >>> <ginsberg@cisco.com>
>> wrote:
>> >>>
>> >>>> Shraddha -
>> >>>>
>> >>>> IGPs today do NOT perform constraint based SPFs - so I don't 
>> >>>> know why you believe that the primary SPF will meet a set of 
>> >>>> constraints that an LFA calculation will not. In fact , it is 
>> >>>> the opposite which is true because implementations today do 
>> >>>> support preferences in choosing LFAs based on various configured 
>> >>>> policy - something which is NOT done for primary SPF.
>> >>>>
>> >>>> If you want a certain class of traffic to avoid a subset of the 
>> >>>> links in the topology then you need to have a way of identifying 
>> >>>> the links (NOT the node addresses) and a way of calculating a 
>> >>>> path which only uses the links which meet the constraints of 
>> >>>> that class of
>> service.
>> >>>> Identifying a particular prefix as protected or unprotected 
>> >>>> won't achieve that.
>> >>>>
>> >>>>  Les
>> >>>>
>> >>>> -----Original Message-----
>> >>>> From: Shraddha Hegde [mailto:shraddha@juniper.net]
>> >>>> Sent: Friday, January 02, 2015 10:54 AM
>> >>>> To: Les Ginsberg (ginsberg); Peter Psenak (ppsenak); 
>> >>>> draft-ietf-ospf-segment-routing-extensions@tools.ietf.org;
>> >>>> draft-ietf-isis-segment-routing-extensions@tools.ietf.org
>> >>>> Cc: ospf@ietf.org; isis-wg@ietf.org
>> >>>> Subject: RE: [Isis-wg] Mail regarding 
>> >>>> draft-ietf-ospf-segment-routing-extensions
>> >>>>
>> >>>> Hi Les/Peter,
>> >>>>
>> >>>>     When reconvergence happens, the primary path will be 
>> >>>> calculated based on all constriants.
>> >>>> This is not true with the protection path.Protection path is 
>> >>>> calculated locally (LFA/RLFA)  and does not consider the 
>> >>>> characteristics of the services running on that path.
>> >>>> It's easier for some services to pick the unprotected path when 
>> >>>> the nature of the service is that it can be restarted  when 
>> >>>> there is a disconnection.
>> >>>>
>> >>>> Rgds
>> >>>> Shraddha
>> >>>> -----Original Message-----
>> >>>> From: Les Ginsberg (ginsberg) [mailto:ginsberg@cisco.com]
>> >>>> Sent: Friday, January 02, 2015 10:06 PM
>> >>>> To: Peter Psenak (ppsenak); Shraddha Hegde; 
>> >>>> draft-ietf-ospf-segment-routing-extensions@tools.ietf.org;
>> >>>> draft-ietf-isis-segment-routing-extensions@tools.ietf.org
>> >>>> Cc: ospf@ietf.org; isis-wg@ietf.org
>> >>>> Subject: RE: [Isis-wg] Mail regarding 
>> >>>> draft-ietf-ospf-segment-routing-extensions
>> >>>>
>> >>>> Peter -
>> >>>>
>> >>>> The requirement Shraddha specified was to not allow a particular 
>> >>>> class of service ("heavy bandwidth services" was the example
>> >>>> provided) to use certain links in the topology. My point is that 
>> >>>> advertising a flag for a given prefix which says "do not 
>> >>>> calculate a repair path for this prefix"
>> >>>> does not help achieve this. Once the network reconverges 
>> >>>> following the failure of one of the links on which "heavy
>>bandwidth services"
>> >>>> is allowed/preferred it is quite likely that the new best path 
>> >>>> will be over a link on which "heavy bandwidth services" is NOT 
>> >>>> allowed/preferred. This will happen whether you have the new 
>> >>>> flag or not - so the flag will have no lasting effect. It would 
>> >>>> only affect traffic flow during the brief period during which 
>> >>>> the network is reconverging.
>> >>>>
>> >>>> I think you and I are actually in agreement - I am simply 
>> >>>> sending a stronger negative message - not only do I think the 
>> >>>> flag is not useful
>> >>>> - I think it does not achieve the goal Shraddha has in mind.
>> >>>>
>> >>>>  Les
>> >>>>
>> >>>>
>> >>>> -----Original Message-----
>> >>>> From: Peter Psenak (ppsenak)
>> >>>> Sent: Friday, January 02, 2015 12:18 AM
>> >>>> To: Les Ginsberg (ginsberg); Shraddha Hegde; 
>> >>>> draft-ietf-ospf-segment-routing-extensions@tools.ietf.org;
>> >>>> draft-ietf-isis-segment-routing-extensions@tools.ietf.org
>> >>>> Cc: ospf@ietf.org; isis-wg@ietf.org
>> >>>> Subject: Re: [Isis-wg] Mail regarding 
>> >>>> draft-ietf-ospf-segment-routing-extensions
>> >>>>
>> >>>> Hi Les,
>> >>>>
>> >>>> I believe the idea is not to exclude any particular link, it's 
>> >>>> actually much simpler - do not calculate backup for the prefix 
>> >>>> if the flag is set.
>> >>>>
>> >>>> I'm still not quite sure how useful above is, but technically it 
>> >>>> is possible.
>> >>>>
>> >>>> thanks,
>> >>>> Peter
>> >>>>
>> >>>> On 12/30/14 17:22 , Les Ginsberg (ginsberg) wrote:
>> >>>>> Shraddha -
>> >>>>>
>> >>>>> When performing a best path calculation whether a given link is 
>> >>>>> in the set of best paths (to be protectedED) or not (could be 
>> >>>>> used as a protectING path) is a function of the topology - not
>>the link.
>> >>>>> If there is a topology change it is quite likely that a given 
>> >>>>> link will change from being a protectED link to being a 
>> >>>>> protectING link (or vice versa).
>> >>>>> So what you propose regarding node-SIDs would not work.
>> >>>>>
>> >>>>> In the use case you mention below if you don't want a certain 
>> >>>>> class of traffic to flow on a given link it requires a link 
>> >>>>> attribute which is persistent across topology changes. There 
>> >>>>> are ways to do that - using Adj-SIDs is one of them. But using 
>> >>>>> node-SIDs in the way you propose is NOT.
>> >>>>>
>> >>>>>    Les
>> >>>>>
>> >>>>> -----Original Message-----
>> >>>>> From: OSPF [mailto:ospf-bounces@ietf.org] On Behalf Of Shraddha 
>> >>>>> Hegde
>> >>>>> Sent: Monday, December 29, 2014 10:12 PM
>> >>>>> To: Peter Psenak (ppsenak);
>> >>>>> draft-ietf-ospf-segment-routing-extensions@tools.ietf.org;
>> >>>>> draft-ietf-isis-segment-routing-extensions@tools.ietf.org
>> >>>>> Cc: ospf@ietf.org; isis-wg@ietf.org
>> >>>>> Subject: Re: [OSPF] [Isis-wg] Mail regarding 
>> >>>>> draft-ietf-ospf-segment-routing-extensions
>> >>>>>
>> >>>>> Peter,
>> >>>>>
>> >>>>>> The requirement here is to get an un-protected path for 
>> >>>>>> services which do not want to divert the traffic on protected
>>path in any case.
>> >>>>>
>> >>>>>> can you give an example of such a service and a reasoning why 
>> >>>>>> such service would want to avoid local protection along the path?
>> >>>>>
>> >>>>> Heavy bandwidth services are potential candidates.  The network 
>> >>>>> is well planned and well provisioned for primary path but same 
>> >>>>> is not true for backup paths.
>> >>>>> Diverting heavy bandwidth services along protection path can 
>> >>>>> disrupt the other services on that path, they are better-off 
>> >>>>> un-protected so that an event in the network Would result in 
>> >>>>> disconnection and a retry for such services.
>> >>>>>
>> >>>>> Rgds
>> >>>>> Shraddha
>> >>>>>
>> >>>>> -----Original Message-----
>> >>>>> From: Peter Psenak [mailto:ppsenak@cisco.com]
>> >>>>> Sent: Monday, December 29, 2014 4:35 PM
>> >>>>> To: Shraddha Hegde;
>> >>>>> draft-ietf-ospf-segment-routing-extensions@tools.ietf.org;
>> >>>>> draft-ietf-isis-segment-routing-extensions@tools.ietf.org
>> >>>>> Cc: ospf@ietf.org; isis-wg@ietf.org
>> >>>>> Subject: Re: [Isis-wg] Mail regarding 
>> >>>>> draft-ietf-ospf-segment-routing-extensions
>> >>>>>
>> >>>>> Shraddha,
>> >>>>>
>> >>>>> On 12/29/14 10:06 , Shraddha Hegde wrote:
>> >>>>>> Peter,
>> >>>>>>
>> >>>>>> The requirement here is to get an un-protected path for 
>> >>>>>> services which do not want to divert the traffic on protected
>>path in any case.
>> >>>>>
>> >>>>> can you give an example of such a service and a reasoning why 
>> >>>>> such service would want to avoid local protection along the path?
>> >>>>>
>> >>>>> thanks,
>> >>>>> Peter
>> >>>>>
>> >>>>>> So when the originator of node-sid signals un-protected path 
>> >>>>>> requirement, there is always an unprotected path.
>> >>>>>>
>> >>>>>> Regarding the protected path, it is the default behavior as it 
>> >>>>>> exists today. You get protection if it's available otherwise 
>> >>>>>> you don't get protection.
>> >>>>>>
>> >>>>>> In fact, you can have the new flag to say "NP flag" meaning 
>> >>>>>> non-protected flag which can be set for the unprotected path.
>> >>>>>> By default it remains off and gives the behavior as it exists
>>today.
>> >>>>>>
>> >>>>>>
>> >>>>>> Rgds
>> >>>>>> Shraddha
>> >>>>>>
>> >>>>>> -----Original Message-----
>> >>>>>> From: Peter Psenak [mailto:ppsenak@cisco.com]
>> >>>>>> Sent: Monday, December 29, 2014 2:26 PM
>> >>>>>> To: Shraddha Hegde;
>> >>>>>> draft-ietf-ospf-segment-routing-extensions@tools.ietf.org;
>> >>>>>> draft-ietf-isis-segment-routing-extensions@tools.ietf.org
>> >>>>>> Cc: ospf@ietf.org; isis-wg@ietf.org
>> >>>>>> Subject: Re: [Isis-wg] Mail regarding 
>> >>>>>> draft-ietf-ospf-segment-routing-extensions
>> >>>>>>
>> >>>>>> Shraddha,
>> >>>>>>
>> >>>>>> I do not see how an originator of the node-sid can mandate a 
>> >>>>>> protection for the prefix on other routers. What if there is 
>> >>>>>> no backup available on a certain node along the path?
>> >>>>>>
>> >>>>>> The parallel with the B-flag in adj-sids is not right - in 
>> >>>>>> case of adj-sid the originator has the knowledge about the 
>> >>>>>> local adjacency protection and as such can signal it it it's LSA.
>> >>>>>>
>> >>>>>> thanks,
>> >>>>>> Peter
>> >>>>>>
>> >>>>>>
>> >>>>>> On 12/29/14 09:47 , Shraddha Hegde wrote:
>> >>>>>>> Peter,
>> >>>>>>>
>> >>>>>>>
>> >>>>>>> Pls see inline.
>> >>>>>>>
>> >>>>>>> Rgds
>> >>>>>>> Shraddha
>> >>>>>>>
>> >>>>>>> -----Original Message-----
>> >>>>>>> From: Peter Psenak [mailto:ppsenak@cisco.com]
>> >>>>>>> Sent: Monday, December 29, 2014 2:02 PM
>> >>>>>>> To: Shraddha Hegde;
>> >>>>>>> draft-ietf-ospf-segment-routing-extensions@tools.ietf.org;
>> >>>>>>> draft-ietf-isis-segment-routing-extensions@tools.ietf.org
>> >>>>>>> Cc: ospf@ietf.org; isis-wg@ietf.org
>> >>>>>>> Subject: Re: [Isis-wg] Mail regarding 
>> >>>>>>> draft-ietf-ospf-segment-routing-extensions
>> >>>>>>>
>> >>>>>>> Shraddha,
>> >>>>>>>
>> >>>>>>> I do not see how an originator can set any flag regarding the 
>> >>>>>>> protection of the locally attached prefix.
>> >>>>>>> <Shraddha> The originator advertises 2 node-sids. One with p 
>> >>>>>>> flag set and the other without the p-flag set.
>> >>>>>>>
>> >>>>>>>    It's all the routers on the path towards such prefix that 
>> >>>>>>> need to deal with the protection.
>> >>>>>>> <Shraddha> The receiving nodes will download protected path 
>> >>>>>>> for the node-sid with p-flag set and download Unprotected 
>> >>>>>>> path for the node-sid with p-flag unset.
>> >>>>>>>
>> >>>>>>> Signaling anything from the originator seems useless.
>> >>>>>>> <Shraddha>  For node-sids it's the others who need to build 
>> >>>>>>> the forwarding plane but it's only the originator who can
>>signal which of
>> >>>>>>>                           Sid need to be built with 
>> >>>>>>> protection and which not. Other routers on the path cannot 
>> >>>>>>> signal this information.
>> >>>>>>
>> >>>>>>
>> >>>>>>
>> >>>>>>>
>> >>>>>>> With this you have two paths for the node. One is protected 
>> >>>>>>> and the other is unprotected. This meets the requirement of 
>> >>>>>>> having an un-protected path.
>> >>>>>>>
>> >>>>>>> It's very much in parallel to B-flag in adj-sids. It is 
>> >>>>>>> similar to advertising multiple adj-sids one with B-flag on 
>> >>>>>>> and other with b-flag off , to get protected and unprotected
>>Adj-sids.
>> >>>>>>>
>> >>>>>>> thanks,
>> >>>>>>> Peter
>> >>>>>>>
>> >>>>>>> On 12/29/14 09:26 , Shraddha Hegde wrote:
>> >>>>>>>> Yes.You are right.
>> >>>>>>>>
>> >>>>>>>> Lets say a prefix sid has a flag "p flag". If this is on it 
>> >>>>>>>> means build a path and provide protection.
>> >>>>>>>> If this is off it means build a path with no protection.
>> >>>>>>>> The receivers of the prefix-sid will build forwarding plane 
>> >>>>>>>> based on this flag.
>> >>>>>>>>
>> >>>>>>>> The applications building the paths will either use 
>> >>>>>>>> prefix-sids with p flag on or off based on the need of the
>>service.
>> >>>>>>>> Rgds
>> >>>>>>>> Shraddha
>> >>>>>>>>
>> >>>>>>>>
>> >>>>>>>> -----Original Message-----
>> >>>>>>>> From: Peter Psenak [mailto:ppsenak@cisco.com]
>> >>>>>>>> Sent: Monday, December 29, 2014 1:49 PM
>> >>>>>>>> To: Shraddha Hegde;
>> >>>>>>>> draft-ietf-ospf-segment-routing-extensions@tools.ietf.org;
>> >>>>>>>> draft-ietf-isis-segment-routing-extensions@tools.ietf.org
>> >>>>>>>> Cc: ospf@ietf.org; isis-wg@ietf.org
>> >>>>>>>> Subject: Re: [Isis-wg] Mail regarding 
>> >>>>>>>> draft-ietf-ospf-segment-routing-extensions
>> >>>>>>>>
>> >>>>>>>> Shraddha,
>> >>>>>>>>
>> >>>>>>>> the problem is that the node that is advertising the 
>> >>>>>>>> node-sid can not advertise any data regarding the protection 
>> >>>>>>>> of such prefix, because the prefix is locally attached.
>> >>>>>>>>
>> >>>>>>>> thanks,
>> >>>>>>>> Peter
>> >>>>>>>>
>> >>>>>>>> On 12/29/14 09:15 , Shraddha Hegde wrote:
>> >>>>>>>>> Peter,
>> >>>>>>>>>
>> >>>>>>>>> If there is a service which has to use un-protected path 
>> >>>>>>>>> and while  building such a path if the node-sids Need to be 
>> >>>>>>>>> used (one reason  could be label stack compression) , then 
>> >>>>>>>>> there has to be unprotected node-sid that this service can 
>> >>>>>>>>> make use
>> of.
>> >>>>>>>>>
>> >>>>>>>>> Prefix -sids could also be used to represent different 
>> >>>>>>>>> service endpoints which makes it even more relevant to have 
>> >>>>>>>>> A means
>> of
>> >>>>>>>>> representing  unprotected paths.
>> >>>>>>>>>
>> >>>>>>>>> Would be good to hear from others on this, especially
>>operators.
>> >>>>>>>>>
>> >>>>>>>>> Rgds
>> >>>>>>>>> Shraddha
>> >>>>>>>>>
>> >>>>>>>>>
>> >>>>>>>>> -----Original Message-----
>> >>>>>>>>> From: Peter Psenak [mailto:ppsenak@cisco.com]
>> >>>>>>>>> Sent: Monday, December 29, 2014 1:35 PM
>> >>>>>>>>> To: Shraddha Hegde;
>> >>>>>>>>> draft-ietf-ospf-segment-routing-extensions@tools.ietf.org;
>> >>>>>>>>> draft-ietf-isis-segment-routing-extensions@tools.ietf.org
>> >>>>>>>>> Cc: ospf@ietf.org; isis-wg@ietf.org
>> >>>>>>>>> Subject: Re: [Isis-wg] Mail regarding 
>> >>>>>>>>> draft-ietf-ospf-segment-routing-extensions
>> >>>>>>>>>
>> >>>>>>>>> Shraddha,
>> >>>>>>>>>
>> >>>>>>>>> node-SID is advertised by the router for the prefix that is 
>> >>>>>>>>> directly attached to it. Protection for such local prefix 
>> >>>>>>>>> does not mean much.
>> >>>>>>>>>
>> >>>>>>>>> thanks,
>> >>>>>>>>> Peter
>> >>>>>>>>>
>> >>>>>>>>> On 12/24/14 11:57 , Shraddha Hegde wrote:
>> >>>>>>>>>> Authors,
>> >>>>>>>>>> We have a "backup flag" in adjacency sid to indicate 
>> >>>>>>>>>> whether the label is protected or not.
>> >>>>>>>>>> Similarly. I think we need a flag in prefix-sid as well to 
>> >>>>>>>>>> indicate whether the node-sid is to be protected or not.
>> >>>>>>>>>> Any thoughts on this?
>> >>>>>>>>>> Rgds
>> >>>>>>>>>> Shraddha
>> >>>>>>>>>>
>> >>>>>>>>>>
>> >>>>>>>>>> _______________________________________________
>> >>>>>>>>>> Isis-wg mailing list
>> >>>>>>>>>> Isis-wg@ietf.org
>> >>>>>>>>>> https://www.ietf.org/mailman/listinfo/isis-wg
>> >>>>>>>>>>
>> >>>>>>>>>
>> >>>>>>>>> .
>> >>>>>>>>>
>> >>>>>>>>
>> >>>>>>>> .
>> >>>>>>>>
>> >>>>>>>
>> >>>>>>> .
>> >>>>>>>
>> >>>>>>
>> >>>>>> .
>> >>>>>>
>> >>>>>
>> >>>>> _______________________________________________
>> >>>>> OSPF mailing list
>> >>>>> OSPF@ietf.org
>> >>>>> https://www.ietf.org/mailman/listinfo/ospf
>> >>>>> .
>> >>>>>
>> >>>>
>> >>>> _______________________________________________
>> >>>> OSPF mailing list
>> >>>> OSPF@ietf.org
>> >>>> https://www.ietf.org/mailman/listinfo/ospf
>> >>>
>> >>
>> >
>> > _______________________________________________
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>> > Isis-wg@ietf.org
>> > https://www.ietf.org/mailman/listinfo/isis-wg
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>> >
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>> >
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