Hi, Acee:
My thought is that the traditional IGP metric is the cost from ingress routers(Ra/Rb) to egress routers(R1/R2/R3) which is illustrated in https://datatracker.ietf.org/doc/html/draft-dunbar-lsr-5g-edge-compute-04#appendix-A. Such metric will be same(because of the ANYCAST address be advertised simultaneously via R1/R2/R3 at the same time for one application server, for example, S1/aa08::4450). But, In the above mentioned scenario, there are other factors to be considered, or other factors may be more signification for the selection of ANYCAST server, for example, the Capacity Index, the Preference Index and other constraints. The egress router(A-ER) now calculate the aggregated metric based on these factors. The derived cost should be considered or added at the IGP SPF calculation to the ANYCAST prefix. There are two way to advertise such additional information: 1) To define another type prefix cost, and also the new Flexalgo algorithm, to indicate that both the traditional prefix metric and this additional aggregated metric should be considered together to select the right egress router 2) To put the additional cost information within the Stub-Link TLV that defined in https://datatracker.ietf.org/doc/html/draft-wang-lsr-stub-link-attributes-03, Both can results in the EPE(Egress Peering Engineering)-like effect. But I am prefer to the second option, because in such scenario, the stub link bandwidth, stub link delay etc factors should also be considered when to select the best egress, they are not the attribute of prefixes. We should also know that for these “no inter-as boundary link”, or ‘stub link’, the associated prefix will not be advertised into the IGP automatically, only the local interface address of the stub link on the egress router will be advertised. Best Regards Aijun Wang China Telecom From: [email protected] <[email protected]> On Behalf Of Acee Lindem (acee) Sent: Sunday, January 16, 2022 10:42 PM To: Linda Dunbar <[email protected]>; Aijun Wang <[email protected]>; John E Drake <[email protected]> Cc: Les Ginsberg (ginsberg) <[email protected]>; Gyan Mishra <[email protected]>; Robert Raszuk <[email protected]>; [email protected] Subject: Re: [Lsr] Seeking feedback to the revised draft-dunbar-lsr-5g-edge-compute Hi Linda, I guess you misunderstood me. Since the only advertises a single aggregated metric, you don’t need a new aggregated cost TLV or to use flex algorithm. Just set the base IGP metric for the prefix to the aggregated metric and IGPs will route based on that metric. Thanks, Acee From: Linda Dunbar <[email protected] <mailto:[email protected]> > Date: Saturday, January 15, 2022 at 8:03 PM To: Acee Lindem <[email protected] <mailto:[email protected]> >, Aijun Wang <[email protected] <mailto:[email protected]> >, John E Drake <[email protected] <mailto:[email protected]> > Cc: "Les Ginsberg (ginsberg)" <[email protected] <mailto:[email protected]> >, Gyan Mishra <[email protected] <mailto:[email protected]> >, Robert Raszuk <[email protected] <mailto:[email protected]> >, "[email protected] <mailto:[email protected]> " <[email protected] <mailto:[email protected]> > Subject: RE: [Lsr] Seeking feedback to the revised draft-dunbar-lsr-5g-edge-compute Acee, John, Robert, and LSR experts: We have updated the draft to reflect the comments and suggestions on the LSR mailing list. https://datatracker.ietf.org/doc/draft-dunbar-lsr-5g-edge-compute/ In particular: - This draft describes using additional site costs to influence the shortest path computation for a specific set of prefixes. As there are a small number of egress routers having those prefixes (or destinations) that need to incorporate site costs in SPF computation, Flexible Algorithms [LSR-FlexAlgo] is used to indicate the need for the site costs to be considered for the specific topologies. Need a Flag in the Flexible Algorithm TLV to indicate that “site-cost” needs to be included for the constrained SPF to reach the Prefix. Therefore, it is not informational draft. The “Site Cost” associated with a prefix (i.e., ANYCAST prefix) can be a value configured on the router to which the prefix is attached. The actual mechanism of assigning “Site Cost” or the detailed algorithm is out of the scope of document The “site cost” change rate is comparable with the rate that the application controller adds or removes the application instances at locations to adjust the workload distribution. Typically, the rate of change could be in days. On rare occasions, there might need rate changes in hours. We have added a section to emphasize that It is important that the “site cost” metric doesn’t change too frequently to avoid route oscillation within the network. Thank you. Linda From: Acee Lindem (acee) <[email protected] <mailto:[email protected]> > Sent: Saturday, January 15, 2022 5:30 AM To: Aijun Wang <[email protected] <mailto:[email protected]> >; John E Drake <[email protected] <mailto:[email protected]> > Cc: Les Ginsberg (ginsberg) <[email protected] <mailto:[email protected]> >; Linda Dunbar <[email protected] <mailto:[email protected]> >; Gyan Mishra <[email protected] <mailto:[email protected]> >; Robert Raszuk <[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 Aijun, Linda, Independent of the ongoing debate on whether advertising the server metrics in the IGPs… Now that the draft is simplified to use a single aggregated metric, why not make the draft informational and use the base IGP metrics? This avoid the burden of adding a new flex algorithm. Thanks, Acee From: Lsr <[email protected] <mailto:[email protected]> > on behalf of Aijun Wang <[email protected] <mailto:[email protected]> > Date: Friday, January 14, 2022 at 10:38 PM To: John E Drake <[email protected] <mailto:[email protected]> > Cc: "Les Ginsberg (ginsberg)" <[email protected] <mailto:[email protected]> >, Linda Dunbar <[email protected] <mailto:[email protected]> >, Gyan Mishra <[email protected] <mailto:[email protected]> >, Robert Raszuk <[email protected] <mailto:[email protected]> >, "[email protected] <mailto:[email protected]> " <[email protected] <mailto:[email protected]> > Subject: Re: [Lsr] Seeking feedback to the revised draft-dunbar-lsr-5g-edge-compute This draft is now proposing one aggregate cost of the application server. The detailed factors can also be included if necessary. But the principle for advertising them should be controllable, as required by other dynamic metrics in IGP. Aijun Wang China Telecom On Jan 15, 2022, at 08:37, John E Drake <[email protected] <mailto:[email protected]> > wrote: This is similar to the issue with the Down/Up proposal. A single metric tells an ingress node nothing about the performance of or load on the individual applications at a given site. Yours Irrespectively, John Juniper Business Use Only From: Aijun Wang <[email protected] <mailto:[email protected]> > Sent: Friday, January 14, 2022 6:58 PM To: John E Drake <[email protected] <mailto:[email protected]> > Cc: Robert Raszuk <[email protected] <mailto:[email protected]> >; Gyan Mishra <[email protected] <mailto:[email protected]> >; Les Ginsberg (ginsberg) <[email protected] <mailto:[email protected]> >; Linda Dunbar <[email protected] <mailto:[email protected]> >; [email protected] <mailto:[email protected]> Subject: Re: [Lsr] Seeking feedback to the revised draft-dunbar-lsr-5g-edge-compute [External Email. Be cautious of content] Hi, John: Here I would also like to hear your own opinions. If not, please see my responses for both you and Robert: https://datatracker.ietf.org/doc/html/draft-ietf-lsr-flex-algo-bw-con-01 has introduced the “delay metric” into the IGP. Such metric may be variant in every link within the IGP. The proposal in draft-dunbar-lsr-5g-edge-compute is only for the stub-link’s/prefixes characteristics, it is the aggregate cost to the server that measured from the router. All the factors that mentioned by Robert maybe the parameters that influences the performance of the server, which will be reflected in the aggregate cost. Then, the conclusion is that IGP has now the capabilities to deal with the dynamics value(the change frequencies can certainly be controlled, thinking how we control the flapping interface)within the network , the aggregate cost or other quasi-static factor to the server at the edge of the network can also be considered together. Such approaches can certainly let the IGP give more optimal behavior to forward the traffic to the appropriate destination, or follow an optimal path. Aijun Wang China Telecom On Jan 14, 2022, at 23:49, John E Drake <[email protected] <mailto:[email protected]> > wrote: Robert is correct on all points. Yours Irrespectively, John Juniper Business Use Only From: Lsr <[email protected] <mailto:[email protected]> > On Behalf Of Robert Raszuk Sent: Friday, January 14, 2022 4:20 AM To: Gyan Mishra <[email protected] <mailto:[email protected]> > Cc: Les Ginsberg (ginsberg) <[email protected] <mailto:[email protected]> >; Linda Dunbar <[email protected] <mailto:[email protected]> >; [email protected] <mailto:[email protected]> Subject: Re: [Lsr] Seeking feedback to the revised draft-dunbar-lsr-5g-edge-compute [External Email. Be cautious of content] Gyan, This is not a network discussion. There are well proven techniques to direct user sessions or user requests to a pool of servers deployed and operational. All provide robust services. Network plays very little to no role in that. There are also lot's of factors involved in making that decision (CPU load, RAM, Storage, IO, CPU Temp etc ...) and IMO it would be very bad to now make IGP to carry it and make routing decisions (even if separate topology) based on that information. I do not see this like a move into the right direction. That is my input. Kind regards, Robert. On Fri, Jan 14, 2022 at 4:53 AM Gyan Mishra <[email protected] <mailto:[email protected]> > wrote: Robert Responses in-line On Thu, Jan 13, 2022 at 5:55 AM Robert Raszuk <[email protected] <mailto:[email protected]> > wrote: Gyan, I see what the draft is trying to do now. /* I did not even consider this for the reason described below. */ But what you wrote requires little correction: "So now the server you are on gets overloaded and a site cost gets advertised in the IGP at which point the connection receives a TCP reset" if you s/connection/all connections/ then you quickly realize that what is proposed here is a disaster. Gyan> Remember this is Anycast proximity based routing along with ECMP / UCMP flow based load balancing and most vendors modern routers support some sort of x-tuple ECMP/UCMP hash so the flows would be evenly distributed, so if you have 10s of 100s of paths, the flows would be evenly distributed across all the paths. Since it’s Anycast proximity each path leads to a different Application LB VIP and backend server. So all the TCP connections would be uniformly distributed across all the paths. Only the connections hashed to the path with overloaded server would get reset and it would be no different then if the server went down as the connections would get reset anyway in that case. In this case instead of being pinned to a bad connection you are now reset to a good connection resulting in better QOE for the end user and a Happy customer. To me thats a positive not a negative. A good analogy would be let’s say you are on WIFI and on the same channel that your neighbors are on and have horrible bandwidth. Do you stay on that bad channel and limp along all day or to you flip to an unused channel. Another example is if you have a server that has run out of resources. Do you fail production traffic off the server taking it out of rotation or let it stay as is and pray things get better. This draft is a good example of how IGP can save the day with site metric. Breaking all existing flows going to one LB to suddenly timeout and all go to the other LB(s) is never a technique any one would seriously deploy in a production network. Gyan> Application load balancing can be done with DNS based GEO load balancing based on client and server IP database where you have more discrete control however the failover is much slower. Leave alone that doing that has potential to immediately overload the other LB(s)/server(s) too. Gyan> The idea with Anycast load balancing is that you may have 10 or even 100s of paths, so if one server fails the load can be evenly distributed based on statistical multiplexing algorithm calculated by the server teams engineering the sizing of the server clusters to ensure what you described won’t happen. For me the conclusion is that IGP transport level is not the proper layer to address the requirement. Cheers, Robert. On Thu, Jan 13, 2022 at 7:05 AM Gyan Mishra <[email protected] <mailto:[email protected]> > wrote: Hi Les Agreed. My thoughts are that the context of the draft is based on an Anycast VIP address of a server which is proximity based load balancing and not necessarily ECMP/UCMP and only if the proximity is the same for multiple paths to the Anycast VIP would there be a ECMP/UCMP possibility. Let’s say if it’s proximity based and one path is preferred, the flow will take that path. So now the server you are on gets overloaded and a site cost gets advertised in the IGP at which point the connection receives a TCP reset and flow re-establishes on the alternate path based on the site cost and remains there until the server goes down or gets overloaded or a better path comes along. For ECMP case, ECMP has flow affinity so the flow will stay on the same path long lived until the connection terminates. So now in ECMP case the flow hashed to a path and maintains its affinity to that path. Now all of sudden the server gets overloaded and we get a better site cost advertised. So now the session terminates on current path and establishes again on the Anycast VIP new path based on the site cost advertised. The failover I believe results in the user refreshing their browser which is better than hanging. As the VIP prefix is the only one that experiences reconvergence on new path based on site cost if there is any instability with the servers that will be reflected to the IGP Anycast prefix as well. Is that a good or bad thing. I think if you had to pick your poison as here the issue Linda is trying to solve is a server issue but leveraging the IGP to force re-convergence when the server is in a half baked state meaning it’s busy and connections are being dropped or very slow QOE for end user. If you did nothing and let it ride the the user would be stuck on a bad connection. So this solution dynamically fixed the issue. As far as oscillation that is not a big deal as you are in a much worse off state connected to a dying server on its last leg as far as memory and CPU. This solution I can see can apply to any client / server connection and not just 5G and can be used by enterprises as well as SP for their customers to have an drastically improved QOE. I saw some feedback on the TLV and I think once that is all worked out I am in favor of advancing this draft. Kind Regards Gyan On Wed, Jan 12, 2022 at 10:16 PM Les Ginsberg (ginsberg) <[email protected] <mailto:[email protected]> > wrote: 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] <mailto:[email protected]> > Sent: Wednesday, January 12, 2022 5:26 PM To: Robert Raszuk <[email protected] <mailto:[email protected]> > Cc: Les Ginsberg (ginsberg) <[email protected] <mailto:[email protected]> >; Linda Dunbar <[email protected] <mailto:[email protected]> >; [email protected] <mailto:[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. _______________________________________________ Lsr mailing list [email protected] <mailto:[email protected]> https://www.ietf.org/mailman/listinfo/lsr -- Gyan Mishra Network Solutions Architect Email [email protected] <mailto:[email protected]> M 301 502-1347 -- Gyan Mishra Network Solutions Architect Email [email protected] <mailto:[email protected]> M 301 502-1347 -- Gyan Mishra Network Solutions Architect Email [email protected] <mailto:[email protected]> M 301 502-1347 _______________________________________________ Lsr mailing list [email protected] <mailto:[email protected]> https://www.ietf.org/mailman/listinfo/lsr <https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.ietf.org%2Fmailman%2Flistinfo%2Flsr&data=04%7C01%7Clinda.dunbar%40futurewei.com%7C5ed0b71fabcb42630bdf08d9d81a6858%7C0fee8ff2a3b240189c753a1d5591fedc%7C1%7C0%7C637778430231799294%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000&sdata=l4ap2Ws%2F8oorV8CCX2avTQwtvmhWLJpqjigDGd2nNa8%3D&reserved=0> _______________________________________________ Lsr mailing list [email protected] <mailto:[email protected]> https://www.ietf.org/mailman/listinfo/lsr
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