Still use the Dijkstra shortest path algorithm. Just the cost to the destination includes more than the routing hops.
Linda From: Robert Raszuk <[email protected]> Sent: Wednesday, January 12, 2022 2:39 PM To: Linda Dunbar <[email protected]> Cc: Les Ginsberg (ginsberg) <[email protected]>; [email protected] Subject: Re: [Lsr] Seeking feedback to the revised draft-dunbar-lsr-5g-edge-compute > IGP cost typically is determined by comparing the preference, then the weight, > then the metric, and finally the metric2 of the two resolving routes. Are we sure we are on the same page here ? Are you describing some new yet to be defined algorithm or Dijkstra ? Thx, R. On Wed, Jan 12, 2022 at 9:36 PM Linda Dunbar <[email protected]<mailto:[email protected]>> wrote: Robert, IGP cost typically is determined by comparing the preference, then the weight, then the metric, and finally the metric2 of the two resolving routes. The draft is to add another site-cost metric to the IGP computation. Using MPLS is too heavy. Linda From: Robert Raszuk <[email protected]<mailto:[email protected]>> Sent: Wednesday, January 12, 2022 1:23 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 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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