Re: [Lsr] WG Adoption Call for "IGP Flexible Algorithms (Flex-Algorithm) In IP Networks" - draft-bonica-lsr-ip-flexalgo-01

Gyan Mishra <hayabusagsm@gmail.com> Fri, 04 December 2020 05:28 UTC

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From: Gyan Mishra <hayabusagsm@gmail.com>
Date: Fri, 4 Dec 2020 00:28:34 -0500
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To: Jeff Tantsura <jefftant.ietf@gmail.com>
Cc: "Acee Lindem (acee)" <acee=40cisco.com@dmarc.ietf.org>, Robert Raszuk <robert@raszuk.net>, Tony Li <tony1athome@gmail.com>, lsr <lsr@ietf.org>
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Subject: Re: [Lsr] WG Adoption Call for "IGP Flexible Algorithms (Flex-Algorithm) In IP Networks" - draft-bonica-lsr-ip-flexalgo-01
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+1 for IP flex algo for operators toolbox

Thanks

On Thu, Dec 3, 2020 at 10:54 PM Jeff Tantsura <jefftant.ietf@gmail.com>
wrote:

> I’m very much in favor of being able to provide a number of technologies
> that help operators with different requirements and constraints to provide
> their services in a most optimized way, hence my support for flex-algo,
> either labeled or not as a technology on the dynamic spectrum of the
> solution space.
> One can achieve similar results on a single topology with a centralized
> controller, there are trade-offs in either, extremities on either side are
> counterproductive .
>
> Regards,
> Jeff
>
> On Dec 3, 2020, at 17:47, Gyan Mishra <hayabusagsm@gmail.com> wrote:
>
> 
>
>
>
> In fact the concept of traffic engineering has been around for a long time
> using simple IGP metric manipulation to steer traffic using the IGP.
>
> I had designed in my past life a costing algorithm where you use highest
> bandwidth links and lowest latency as the crow flies point A to point B
> such that you take the highest bandwidth lowest latency path based on a
> formula for path instantiation.  This is the essence of flex algo basically
> an engineered algorithm algo xyz for a sub routing instance instantiation.
>
> This concept works well for global table or single routing instance,
> however if you have multiple VPNs and you want to realize per VPN coloring
> capabilities it is much different then use of flex algo with a single IGP
> global table routing following a single algo or multiple sub set algo’s.
>
> That’s where RSVP TE PCALC path computation and bandwidth and link
> attributes came into play in an MPLS context.
>
> However, now trying to expand traditional RSVP TE to provide per VRF VPN
> mapping and coloring is now a daunting painful and non scalable solution.
> Now requires with RSVP static routes and VRF next hop rewrite to map each
> VPN to a different color steered statically to a different loopback egress
> PE iBGP next hop then the default iBGP global table next hop.
>
> That’s where the advent of SR with SR-TE now fills that much needed gap of
> per VRF coloring to build the same as we had in the RSVP world loose path
> prefix sid or strict path adjacency sid path instantiation now done via
> centralized controller.
>
> The gap where flex algo comes into play is unique but I think is a tool on
> the operator toolbox which prior to IP flex algo provided additional
> steering granularity and path instantiation control used in conjunction
> with SR-TE.
>
> The gap IP flex algo fills is internet providers global table routing
> being able to create logical traffic steering constructs where MPLS or SR
> does not exist.
>
> So that is a huge much needed gap as not all operators on the public core
> have MPLS or SR and would like an alternative.
>
> This could be used in both core and data center space as well IP based
> infrastructure.
>
> RSVP TE and SR have their niche and now IP flex algo fills yet another
> somewhat mutually exclusive niche.
>
> Kind Regards
>
> Gyan
>
> On Thu, Dec 3, 2020 at 8:18 PM Jeff Tantsura <jefftant.ietf@gmail.com>
> wrote:
>
>> Anything else than IGP metric based SPT is considered TE. Looking
>> holistically - topology virtualization (or similar) could have been a
>> better name.
>>
>> Cheers,
>> Jeff
>> On Dec 3, 2020, 4:25 PM -0800, Robert Raszuk <robert@raszuk.net>et>, wrote:
>>
>> Hi Tony,
>>
>> The moment I hit "Send" I knew that this response may be coming as it
>> really depends what is one's definition of TE.
>>
>> If indeed IGP TE is anything more then SPF - then sure we can call it a
>> TE feature.
>>
>> However, while a very useful and really cool proposal, my point is to
>> make sure this is not oversold - that's all.
>>
>> Best,
>> R.
>>
>>
>> On Fri, Dec 4, 2020 at 1:13 AM Tony Li <tony1athome@gmail.com> wrote:
>>
>>>
>>> Hi Robert,
>>>
>>>
>>> > However I really do not think that what Flexible Algorithm offers can
>>> be compared or even called as Traffic Engineering (MPLS or SR).
>>> >
>>> > Sure Flex Algo can accomplish in a very elegant way with little cost
>>> multi topology routing but this is not full TE. It can also direct traffic
>>> based on static or dynamic network preferences (link colors, rtt drops etc
>>> ... ),  but again it is not taking into account load of the entire network
>>> and IMHO has no way of accomplish TE level traffic distribution.
>>> >
>>> > Just to make sure the message here is proper.
>>>
>>>
>>> It’s absolutely true that FlexAlgo (IP or SR) has limitations. There’s
>>> no bandwidth reservation. There’s no dynamic load balancing. No, it’s not a
>>> drop in replacement for RSVP. No, it does not supplant SR-TE and a good
>>> controller. Etc., etc., etc….
>>>
>>> However I don’t feel that it’s fair to say that FlexAlgo can’t be called
>>> Traffic Engineering.  After all TE is a very broad topic. Everything that
>>> we’ve done that’s more sophisticated than simple SPF falls in the area of
>>> Traffic Engineering.  Link coloring and SRLG alone clearly fall into that
>>> bucket.
>>>
>>> I’ll grant you that it may not have the right TE features for your
>>> application, but that doesn’t mean that it’s not sufficient for some.
>>> Please don’t mislead people by saying that it’s not Traffic Engineering.
>>>
>>> Regards,
>>> Tony
>>>
>>>
>>> _______________________________________________
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>>
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> --
>
> <http://www.verizon.com/>
>
> *Gyan Mishra*
>
> *Network Solutions A**rchitect *
>
>
>
> *M 301 502-134713101 Columbia Pike
> <https://www.google.com/maps/search/13101+Columbia+Pike+Silver+Spring,+MD?entry=gmail&source=g> *Silver
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> <https://www.google.com/maps/search/13101+Columbia+Pike+Silver+Spring,+MD?entry=gmail&source=g>
>
> --

<http://www.verizon.com/>

*Gyan Mishra*

*Network Solutions A**rchitect *



*M 301 502-134713101 Columbia Pike *Silver Spring, MD