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)" <[email protected]> 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:[email protected]] >Sent: Sunday, January 04, 2015 8:51 AM >To: Les Ginsberg (ginsberg); Shraddha Hegde; Peter Psenak (ppsenak); >[email protected]; >[email protected] >Cc: [email protected]; [email protected] >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)" <[email protected]> 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:[email protected]] >>Sent: Friday, January 02, 2015 10:54 AM >>To: Les Ginsberg (ginsberg); Peter Psenak (ppsenak); >>[email protected]; >>[email protected] >>Cc: [email protected]; [email protected] >>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:[email protected]] >>Sent: Friday, January 02, 2015 10:06 PM >>To: Peter Psenak (ppsenak); Shraddha Hegde; >>[email protected]; >>[email protected] >>Cc: [email protected]; [email protected] >>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; >>[email protected]; >>[email protected] >>Cc: [email protected]; [email protected] >>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:[email protected]] On Behalf Of Shraddha Hegde >>> Sent: Monday, December 29, 2014 10:12 PM >>> To: Peter Psenak (ppsenak); >>> [email protected]; >>> [email protected] >>> Cc: [email protected]; [email protected] >>> 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:[email protected]] >>> Sent: Monday, December 29, 2014 4:35 PM >>> To: Shraddha Hegde; >>> [email protected]; >>> [email protected] >>> Cc: [email protected]; [email protected] >>> 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:[email protected]] >>>> Sent: Monday, December 29, 2014 2:26 PM >>>> To: Shraddha Hegde; >>>> [email protected]; >>>> [email protected] >>>> Cc: [email protected]; [email protected] >>>> 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:[email protected]] >>>>> Sent: Monday, December 29, 2014 2:02 PM >>>>> To: Shraddha Hegde; >>>>> [email protected]; >>>>> [email protected] >>>>> Cc: [email protected]; [email protected] >>>>> 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:[email protected]] >>>>>> Sent: Monday, December 29, 2014 1:49 PM >>>>>> To: Shraddha Hegde; >>>>>> [email protected]; >>>>>> [email protected] >>>>>> Cc: [email protected]; [email protected] >>>>>> 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:[email protected]] >>>>>>> Sent: Monday, December 29, 2014 1:35 PM >>>>>>> To: Shraddha Hegde; >>>>>>> [email protected]; >>>>>>> [email protected] >>>>>>> Cc: [email protected]; [email protected] >>>>>>> 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 >>>>>>>> [email protected] >>>>>>>> https://www.ietf.org/mailman/listinfo/isis-wg >>>>>>>> >>>>>>> >>>>>>> . >>>>>>> >>>>>> >>>>>> . >>>>>> >>>>> >>>>> . >>>>> >>>> >>>> . >>>> >>> >>> _______________________________________________ >>> OSPF mailing list >>> [email protected] >>> https://www.ietf.org/mailman/listinfo/ospf >>> . >>> >> >>_______________________________________________ >>OSPF mailing list >>[email protected] >>https://www.ietf.org/mailman/listinfo/ospf > _______________________________________________ OSPF mailing list [email protected] https://www.ietf.org/mailman/listinfo/ospf
