Hi Aijun, Please check inline below.
On Fri, Apr 22, 2022 at 8:57 AM Aijun Wang <[email protected]> wrote: > Hi, Ketan and Acee: > > I have not seen there is any other possible application of the “Reverse > Metric” mechanism, except that are described in RFC8500. > > There is no additional value to repeat to illustrate them, refer to them > is enough. > KT> I am considering this as an editorial comment. As explained by me and also confirmed by Acee, there are significant differences in the applicability of the use-cases given that the OSPF reverse metric does not apply for the LAN. That said, we (authors) will be posting an update next week to address the comments received and I believe they will partially incorporate your feedback. > > > The “W” bit in RFC8500 is useful in LAN environment and I have said that > there is no technical issue to apply the “Reverse Metric” mechanism to LAN > environment. > > From my POV, such solution is more straightforward than the 2-part metric > based solution. > KT> The OSPF reverse metric cannot be applied to LAN similar to how it is done in ISIS due to some fundamental differences between the protocols. If you have worked out a solution to the LAN problem that is significantly better than the OSPF Two-Part Metric mechanism and one that leverages Reverse Metric, then I am eager to see it. Please provide the solution and the WG can evaluate it. Thanks, Ketan > > > The existing implementation doesn’t imply it is the best. > > > > Anyway, you can insist your direction. > > > > Best Regards > > > > Aijun Wang > > China Telecom > > > > *From:* [email protected] <[email protected]> *On Behalf Of *Ketan > Talaulikar > *Sent:* Thursday, April 21, 2022 11:00 PM > *To:* Acee Lindem (acee) <[email protected]> > *Cc:* Les Ginsberg (ginsberg) <[email protected]>; Aijun Wang < > [email protected]>; [email protected]; > lsr <[email protected]> > *Subject:* Re: [Lsr] Working Group Last Call for > draft-ietf-lsr-ospf-reverse-metric - "OSPF Reverse Metric" > > > > Hi Aijun, > > > > +1 to Acee's response. > > > > Thanks, > > Ketan > > > > > > On Thu, Apr 21, 2022 at 7:28 PM Acee Lindem (acee) <[email protected]> wrote: > > Speaking as WG member and Document Shepherd: > > > > Hi Aijun, > > > > There is no requirement to directly follow the encodings and terminology > in RFC 8500. In fact, this draft is, IMO, cleaner. > > > > *From: *Aijun Wang <[email protected]> > *Date: *Wednesday, April 20, 2022 at 8:52 PM > *To: *'Ketan Talaulikar' <[email protected]> > *Cc: *"Les Ginsberg (ginsberg)" <[email protected]>, 'lsr' <[email protected]>, > "[email protected]" < > [email protected]>, Acee Lindem <[email protected]> > *Subject: *RE: [Lsr] Working Group Last Call for > draft-ietf-lsr-ospf-reverse-metric - "OSPF Reverse Metric" > > > > Hi, Ketan: > > For document integrity, I think you can write the following corresponding > parts of RFC8500: > > 1) 1.1 Node and Link Isolation > > 2) 1.2 Spine-Leaf Applications(with the term “Congested” to be > replaced by “broken down”) > > 3) 1.3 Distributed Forwarding Planes > > 4) 1.4 LDP IGP Synchronization(Although RFC8042 can solve such > problem, it doesn’t prevent the usage of “Reverse Metric” mechanism to > solve it) > > Or ,you just refer to the above parts in your documents, and avoid to > repeat the scenarios again. > > > > As Ketan already indicated, some of these use cases aren’t applicable for > various reason, e.g., 2-part metric. > > > > For the encoding, I still think you need only specify the metric value is > offset directly(as that in RFC8500), and needn’t introduce the H/O bit to > complex the implementation and deployments. > > > > There may already be implementations and no one has complained. Note that > this draft doesn’t include the W-Bit or U-Bit that are in RFC 8500. It is > more straight-forward. > > > > Thanks, > > Acee > > > > > > Best Regards > > > > Aijun Wang > > China Telecom > > > > *From:* Ketan Talaulikar <[email protected]> > *Sent:* Wednesday, April 20, 2022 6:47 PM > *To:* Aijun Wang <[email protected]> > *Cc:* Les Ginsberg (ginsberg) <[email protected]>; lsr < > [email protected]>; [email protected]; Acee Lindem > (acee) <[email protected]> > *Subject:* Re: [Lsr] Working Group Last Call for > draft-ietf-lsr-ospf-reverse-metric - "OSPF Reverse Metric" > > > > Hi Aijun, > > > > Please check inline below. > > > > > > On Wed, Apr 20, 2022 at 7:36 AM Aijun Wang <[email protected]> > wrote: > > Hi, Ketan: > > My suggestion is to refer some contents in RFC8500, don’t need to > describe the scenarios again, to introduce the necessary of protocol > extension in OSPF. > > > > KT> I am not sure that I understand your suggestion. Which specific > portions of the text would you like to be removed and instead point to the > ISIS Reverse metric spec in a manner that does not affect the readability > of the document. > > > > > > For your mentioned use case 2.2 “Adaptive Metric Signaling”, also the > application described in section 1.3 of RFC 8500(Spine-Leaf Application), > my comments are still the same: > > 1. The described problem is valid, but the “Reversed Metric” based > proposed solution is problematic. > > 2. Here are the explanations( Take your use case 2.2 as the example): > > 1）Normally all the leaf routers(R1, R2,… … Rn) will have the same metric > to the Spine(AGG1, AGG2), the traffic from these leafs will be evenly > distributed to/from AGG1 and AGG2. > > 2) Once the uplink AGG1 encounter the congestion, if it push the “Reverse > Metric” to R1, then all traffic from R1 will divert to AGG2; > > > > KT> I think the use of the term "congestion" seems to be the cause of some > confusion. This is about AGG1 losing some of its capacity towards the core > due to an upstream link going down. We can remove the use of the term > "congestion" in this context. > > > > 3) Will the uplink on AGG2 encounter congestion then? If so, it should > also push the “Reverse Metric” to R1, then all traffic from R1 will back > to AGG1(when the uplink congestion of AGG1 is released, AGG1 will stop send > the “Reverse Metric”) > > > > KT> Please see my previous response. > > > > Thanks, > > Ketan > > > > The traffic from R1 will oscillate between AGGR1 and AGGR2. This is not > the traffic engineering result that the operator want. > > > > Then, my suggestion is that this use case should also be removed. The > application of “Reverse Metric” mechanism should not be expanded, it > should be triggered by manual, not automatically. > > > > Regarding to the encoding, RFC8500 proposes only the offset value, there > are only U/W flag being defined. The “U” bit just indicates the maximum > value is (2^24-1)(corresponding to the “wide”metric). > > > > Considering that the only applicable scenarios is for maintenance, the > introduction of H/U bit complexes its usage. It should be simplified. > > > > > > Best Regards > > > > Aijun Wang > > China Telecom > > > > *From:* Ketan Talaulikar <[email protected]> > *Sent:* Tuesday, April 19, 2022 6:59 PM > *To:* Aijun Wang <[email protected]> > *Cc:* Les Ginsberg (ginsberg) <[email protected]>; Acee > Lindem (acee) <[email protected]>; lsr <[email protected]>; > [email protected] > *Subject:* Re: [Lsr] Working Group Last Call for > draft-ietf-lsr-ospf-reverse-metric - "OSPF Reverse Metric" > > > > Hi Aijun, > > > > Please check inline below for responses. > > > > > > On Tue, Apr 19, 2022 at 1:00 PM Aijun Wang <[email protected]> > wrote: > > Hi, All: > > I have the similar opinions as Les. > > Such mechanism is actually one maintenance tools and can’t be used to > accomplish the metric auto adjustment, as that described in section 2.1 > > > > KT> Please check my response to Les and let us know if that is not > addressing your concerns. > > > > The scenario described in section 2.2 is somewhat problematic: AGGR1 > should calculate the adjusted metric value based on its POV, but the > adjustment will influence the traffic distribution within all the IGP > domain. Such automatic adjustment is dangerous, and is not one solution > that can be applied for the more general scenario. > > > > KT> Any time the IGP metric is updated for a link, it does influence the > traffic distribution in the IGP domain. This is a given and so I don't > really understand your concern. This use case is very similar to the Spine > Leaf one in RFC8500 - we can clarify that in the text. > > > > > > Based on the above considerations, I think the authors should limit its > usage only for maintenance scenarios as described in RFC8500. > > For the encoding, I think the “offset” value and the “O” bit is not > necessary, because the meaningful “Reverse Metric” should be the maximum > value of the metric. > > > > KT> The additive offset is there in RFC8500 as well and so I don't see why > we would want to not have that in OSPF. > > > > Thanks, > > Ketan > > > > > > Best Regards > > > > Aijun Wang > > China Telecom > > > > *From:* [email protected] <[email protected]> *On Behalf Of *Les > Ginsberg (ginsberg) > *Sent:* Tuesday, April 19, 2022 2:44 PM > *To:* Acee Lindem (acee) <[email protected]>; [email protected] > *Cc:* [email protected] > *Subject:* Re: [Lsr] Working Group Last Call for > draft-ietf-lsr-ospf-reverse-metric - "OSPF Reverse Metric" > > > > I support progressing this draft. > > However, I have some concerns about the current content – specifically > the use cases – which I would like to see addressed before going to Last > Call. > > > > The equivalent functionality is defined in RFC 8500 for IS-IS and has > proven useful – make sense to also have it for OSPF. > > But the primary use case discussed in RFC 8500 is during maintenance – > which is discussed extensively and is mentioned as the first use case. > > In the case of draft-ietf-lsr-ospf-reverse-metric, the maintenance use > case is not even mentioned. > > > > Of the two use cases that are mentioned, the one in Section 2.1 has many > limitations and constraints. These include: > > > > · Only works when there is a switch in the middle – something which > the protocol is not able to detect > > · Only works in the presence of symmetrical metrics > > · If both neighbors have L2 bundles to the switch and are both > doing auto-cost adjustment based on the number of members currently up, the > mechanism doesn’t work > > · Detecting symmetrical metrics in the presence of reverse metric > is problematical. Is the neighbor cost including the reverse metric or does > it reflect something else (e.g., config change on the neighbor) > > > > I would prefer that this use case be removed. If not, a more complete > discussion of the limitations should be included. > > > > In summary, before progressing this draft I would like to see maintenance > included as the primary use case and the use case described in Section 2.1 > removed. > > > > Les > > > > > > *From:* Lsr <[email protected]> *On Behalf Of *Acee Lindem (acee) > *Sent:* Thursday, April 7, 2022 12:18 PM > *To:* [email protected] > *Cc:* [email protected] > *Subject:* [Lsr] Working Group Last Call for > draft-ietf-lsr-ospf-reverse-metric - "OSPF Reverse Metric" > > > > This begins a Working Group Last Call for > draft-ietf-lsr-ospf-reverse-metric. While there hasn’t been as much > discussion as I would like on the draft, it is filling a gap in OSPF > corresponding to IS-IS Reverse Metric (RFC 8500). Please review and send > your comments, support, or objection to this list before 12 AM UTC on April > 22nd, 2022. > > > > Thanks, > > Acee > > > > _______________________________________________ > Lsr mailing list > [email protected] > https://www.ietf.org/mailman/listinfo/lsr > > _______________________________________________ > Lsr mailing list > [email protected] > https://www.ietf.org/mailman/listinfo/lsr >
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