Re: [Lsr] draft-ietf-lsr-flex-algo

Peter Psenak <ppsenak@cisco.com> Tue, 19 May 2020 07:38 UTC

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To: Gyan Mishra <hayabusagsm@gmail.com>, "Wang, Weibin (NSB - CN/Shanghai)" <weibin.wang@nokia-sbell.com>
Cc: "lsr@ietf.org" <lsr@ietf.org>, Jeff Tantsura <jefftant.ietf@gmail.com>, "Ketan Talaulikar (ketant)" <ketant@cisco.com>
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From: Peter Psenak <ppsenak@cisco.com>
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Date: Tue, 19 May 2020 09:38:08 +0200
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Archived-At: <https://mailarchive.ietf.org/arch/msg/lsr/7-VE3tmgxFZAPf1tH3k_vBfN7Cw>
Subject: Re: [Lsr] draft-ietf-lsr-flex-algo
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Gyan,

On 19/05/2020 03:52, Gyan Mishra wrote:
> 
> Flex algo is usually mentioned in the context of SR-TE to help reduced 
> SRH size to circumvent MSD issues for both SRV6 and SR-MPLS, 

though segment list reduction may be seen as one of the benefits of the 
flex-algo, it is certainly not the primary motivation behind it. The 
primary motivation of flex-algo is to provide dynamic any to any 
constrained based routing.

> however can 
> the 0-127 flex algo extensions since it’s an IGP extension used in any 
> pure IP network independent of SR flavors SR-MPLS or SRv6.

SR/SRv6 is used as a dataplane. Any data plane can be used, if it 
provides a way to route an algo specific traffic.

> 
> Also can flex algo be used in conjunction with RSVP-TE or PPR(preferred 
> path routing).

same answer as above.

thanks,
Peter

> 
> Kind regards
> 
> Gyan
> 
> On Sat, May 9, 2020 at 9:25 PM Wang, Weibin (NSB - CN/Shanghai) 
> <weibin.wang@nokia-sbell.com <mailto:weibin.wang@nokia-sbell.com>> wrote:
> 
>     Jeff, I see what you said, thank you for sharing information;____
> 
>     __ __
> 
>     __ __
> 
>     __ __
> 
>     Cheers!
> 
>     ____
> 
>     __ __
> 
>     Wang Weibin____
> 
>     __ __
> 
>     *From:* Jeff Tantsura <jefftant.ietf@gmail.com
>     <mailto:jefftant.ietf@gmail.com>>
>     *Sent:* 2020年5月10日 3:24
>     *To:* Wang, Weibin (NSB - CN/Shanghai) <weibin.wang@nokia-sbell.com
>     <mailto:weibin.wang@nokia-sbell.com>>
>     *Cc:* Ketan Talaulikar (ketant) <ketant@cisco.com
>     <mailto:ketant@cisco.com>>; lsr@ietf.org <mailto:lsr@ietf.org>
>     *Subject:* Re: [Lsr] draft-ietf-lsr-flex-algo____
> 
>     __ __
> 
>     Weibin,____
> 
>     __ __
> 
>     One could have an algo with MSD/ERLD as optimizations constrains,
>     would be quite similar to colored links. Note - ERLD has implemented
>     node capabilities only, so all links on a node will have to be
>     pruned.____
> 
>     The tradeoffs are - having centralized controller with global view
>     computing a path that meets the constraints(classical BGP-LS + PCEP
>     scenario) vs building a dynamic topology of connected nodes that
>     meet a set of constrains, in first case, change in
>     topology/capabilities would cause path recalculation/reoptimization
>     on the PCE while in the second - IGP would recompute the topology
>     locally.____
> 
>     __ __
> 
>     Regards,____
> 
>     Jeff____
> 
> 
> 
>     ____
> 
>         On May 9, 2020, at 01:27, Wang, Weibin (NSB - CN/Shanghai)
>         <weibin.wang@nokia-sbell.com
>         <mailto:weibin.wang@nokia-sbell.com>> wrote:____
> 
>         ____
> 
>         Ketan, thank you for clarification.____
> 
>         ____
> 
>         ____
> 
>         ____
> 
>         Cheers!____
> 
>         ____
> 
>         Wang Weibin____
> 
>         ____
> 
>         *From:* Ketan Talaulikar (ketant) <ketant@cisco.com
>         <mailto:ketant@cisco.com>>
>         *Sent:* 2020年5月9日 14:52
>         *To:* Wang, Weibin (NSB - CN/Shanghai)
>         <weibin.wang@nokia-sbell.com
>         <mailto:weibin.wang@nokia-sbell.com>>; lsr@ietf.org
>         <mailto:lsr@ietf.org>
>         *Subject:* RE: draft-ietf-lsr-flex-algo____
> 
>         ____
> 
>         Hi Wang,____
> 
>         ____
> 
>         You are correct. Though I wouldn’t call it a goal but rather a
>         benefit/advantage – same applies to SR-MPLS where the label
>         stack can be reduced.____
> 
>         ____
> 
>         Thanks,____
> 
>         Ketan____
> 
>         ____
> 
>         *From:* Lsr <lsr-bounces@ietf.org <mailto:lsr-bounces@ietf.org>>
>         *On Behalf Of *Wang, Weibin (NSB - CN/Shanghai)
>         *Sent:* 08 May 2020 19:07
>         *To:* lsr@ietf.org <mailto:lsr@ietf.org>
>         *Subject:* [Lsr] draft-ietf-lsr-flex-algo____
> 
>         ____
> 
>         Hi authors:____
> 
>         ____
> 
>         After reading through this draft lsr-flex-algo, I want to know
>         whether there is a potential goal of this draft to reduce the
>         SRH size with enabling flex-algo with admin group in SRv6
>         deployment, because without flex-algo we have to have a big SRH
>         size when the SRH include more SRv6 SIDs, if we enable flex-algo
>         under special topology and link constraint condition, in theory
>         we can even construct  a end to end SR path/tunnel without SRH,
>         but it still meet TE requirement. So my question is whether the
>         flex-algo can be used as tool to reduce SRH size?____
> 
>         ____
> 
>         ____
> 
>         ____
> 
>         /Cheers !/____
> 
>         **____
> 
>         *WANG Weibin*____
> 
>         _______________________________________________
>         Lsr mailing list
>         Lsr@ietf.org <mailto:Lsr@ietf.org>
>         https://www.ietf.org/mailman/listinfo/lsr____
> 
>     _______________________________________________
>     Lsr mailing list
>     Lsr@ietf.org <mailto:Lsr@ietf.org>
>     https://www.ietf.org/mailman/listinfo/lsr
> 
> -- 
> 
> Gyan  Mishra
> 
> Network Engineering & Technology
> 
> Verizon
> 
> Silver Spring, MD 20904
> 
> Phone: 301 502-1347
> 
> Email: gyan.s.mishra@verizon.com <mailto:gyan.s.mishra@verizon.com>
> 
> 
>