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 <[email protected]>
Sent: Wednesday, January 12, 2022 5:26 PM
To: Robert Raszuk <[email protected]>
Cc: Les Ginsberg (ginsberg) <[email protected]>; Linda Dunbar
<[email protected]>; [email protected]
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
<[email protected]<mailto:[email protected]>> 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
<[email protected]<mailto:[email protected]>> wrote:
Robert,
Please see inline in green:
From: Robert Raszuk <[email protected]<mailto:[email protected]>>
Sent: Wednesday, January 12, 2022 1:00 PM
To: Linda Dunbar <[email protected]<mailto:[email protected]>>
Cc: Les Ginsberg (ginsberg) <[email protected]<mailto:[email protected]>>;
[email protected]<mailto:[email protected]>
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
Email [email protected]<mailto:[email protected]>
M 301 502-1347
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