Re: [Lsr] Seeking feedback to the revised draft-dunbar-lsr-5g-edge-compute

["Les Ginsberg (ginsberg)" <[e-mail]>]

Gyan –

The difference between ECMP and UCMP is not significant in this discussion.
I don’t want to speak for Robert, but for me his point was that IGPs can do “multipath” well – but this does not translate into managing flows.
Please see my other responses on this thread.

Thanx.

    Les


From: Gyan Mishra <[e-mail]>
Sent: Wednesday, January 12, 2022 5:26 PM
To: Robert Raszuk <[e-mail]>
Cc: Les Ginsberg (ginsberg) <[e-mail]>; Linda Dunbar <[e-mail]>; [e-mail]
Subject: Re: [Lsr] Seeking feedback to the revised draft-dunbar-lsr-5g-edge-compute


Robert

Here are a few examples of UCMP drafts below used in core and data center use cases.

https://datatracker.ietf.org/doc/html/draft-ietf-bess-evpn-unequal-lb-15

https://datatracker.ietf.org/doc/html/draft-mohanty-bess-weighted-hrw-02

https://datatracker.ietf.org/doc/html/draft-ietf-idr-link-bandwidth

https://datatracker.ietf.org/doc/html/draft-mohanty-bess-ebgp-dmz



There are many use cases in routing for unequal cost load balancing capabilities.

Kind Regards

Gyan

On Wed, Jan 12, 2022 at 2:23 PM Robert Raszuk <[e-mail]<mailto:[e-mail]>> wrote:
Linda,

> IGP has been used for the Multi-path computation for a long time

IGP can and does ECMP well. Moreover, injecting metric of anycast server destination plays no role in it as all paths would inherit that external to the IGP cost.

Unequal cost load balancing or intelligent traffic spread has always been done at the application layer *for example MPLS*

Thx a lot,
R.

On Wed, Jan 12, 2022 at 8:18 PM Linda Dunbar <[e-mail]<mailto:[e-mail]>> wrote:
Robert,

Please see inline in green:

From: Robert Raszuk <[e-mail]<mailto:[e-mail]>>
Sent: Wednesday, January 12, 2022 1:00 PM
To: Linda Dunbar <[e-mail]<mailto:[e-mail]>>
Cc: Les Ginsberg (ginsberg) <[e-mail]<mailto:[e-mail]>>; [e-mail]<mailto:[e-mail]>
Subject: Re: [Lsr] Seeking feedback to the revised draft-dunbar-lsr-5g-edge-compute

Hi Linda,


[LES:] It is my opinion that what you propose will not achieve your goals – in part because IGPs only influence forwarding on a per packet basis – not a per flow/connection basis.

[Linda] Most vendors do support flow based ECMP, with Shortest Path computed by attributes advertised by IGP.

I am with Les here. ECMP has nothing to do with his point.

[Linda] Les said that “IGP only influence forwarding on a per packet basis”.  I am saying that vendors supporting “forwarding per flow” with equal cost computed by IGP implies  that forwarding on modern routers are no longer purely per packet basis.


Draft says:

When those multiple server instances share one IP address (ANYCAST), the transient network and load conditions can be incorporated in selecting an optimal path among server instances for UEs.

So if we apply any new metric to indicate load of a single anycast address how is this going to help anything ?

[Linda] The “Load” or “Aggregated Site Cost” is to differentiate multiple paths with the same routing distance.


You would need a mechanism where the network is smart and say per src-dst tuple or more spreads the traffic. IGP does not play that game today I am afraid.
[Linda] There is one SRC and multiple paths to one DST. IGP has been used for the Multi-path computation for a long time.

Thank you, Linda

Thx a lot,
R.







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Gyan Mishra

Network Solutions Architect

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