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
