Huzhibo,
Pls see inline.. Juniper Business Use Only From: Huzhibo <huzhibo=40huawei....@dmarc.ietf.org> Sent: Friday, January 28, 2022 12:04 PM To: Shraddha Hegde <shrad...@juniper.net>; bruno.decra...@orange.com; SPRING WG <spring@ietf.org> Subject: RE: WG adoption call - draft-hu-spring-segment-routing-proxy-forwarding [External Email. Be cautious of content] Shraddha, Pls see inline for replies. From: Shraddha Hegde [mailto:shraddha=40juniper....@dmarc.ietf.org] Sent: Friday, January 28, 2022 12:20 PM To: Huzhibo <huzh...@huawei.com<mailto:huzh...@huawei.com>>; bruno.decra...@orange.com<mailto:bruno.decra...@orange.com>; SPRING WG <spring@ietf.org<mailto:spring@ietf.org>> Subject: RE: WG adoption call - draft-hu-spring-segment-routing-proxy-forwarding Huzhibo, Pls see inline for replies.. Juniper Business Use Only From: Huzhibo <huzhibo=40huawei....@dmarc.ietf.org<mailto:huzhibo=40huawei....@dmarc.ietf.org>> Sent: Thursday, January 27, 2022 2:59 PM To: Shraddha Hegde <shrad...@juniper.net<mailto:shrad...@juniper.net>>; bruno.decra...@orange.com<mailto:bruno.decra...@orange.com>; SPRING WG <spring@ietf.org<mailto:spring@ietf.org>> Subject: RE: WG adoption call - draft-hu-spring-segment-routing-proxy-forwarding [External Email. Be cautious of content] Hi Shraddha: Thanks for your comments, Please see inline. Thanks Zhibo Hu From: spring [mailto:spring-boun...@ietf.org] On Behalf Of Shraddha Hegde Sent: Thursday, January 27, 2022 3:15 PM To: bruno.decra...@orange.com<mailto:bruno.decra...@orange.com>; SPRING WG <spring@ietf.org<mailto:spring@ietf.org>> Subject: Re: [spring] WG adoption call - draft-hu-spring-segment-routing-proxy-forwarding WG, I don’t support the adoption of this document as a WG document. I am in agreement with stephane’s comments on the list. 1. May cause congestion somewhere else in the network There is already WG adopted document that is addressing the problem space draft-ietf-spring-segment-protection-sr-te-paths. This draft does not provide significant advantages over the proposed solutions in draft-ietf-spring-segment-protection-sr-te-paths. draft-hu-spring-segment-routing-proxy-forwarding claims to provide better solution when all nodes have not been upgraded. draft-hu-spring-segment-routing-proxy-forwarding introduces protocol extensions and the nodes that aren’t upgraded to understand the extensions will drop the traffic so there isn’t any significant improvement in the approach. In fact, the approach described in draft-hu-spring-segment-routing-proxy-forwarding may cause other issues such as bandwidth double booking since it proposes that any neighbor that claims proxy forwarding will be used to forward the protected traffic. For ex: [cid:image001.jpg@01D8144D.30DC4950] In above diagram SR-TE path is RT1->RT3->RT7->RT5 Only RT4 supports proxy-forwarding On failure of RT3, RT1 would send traffic to RT4 via RT1->RT6->RT7-RT4 RT4 will then send to RT7 as per the SR-TE path RT7 will then send to RT5 via RT7->RT4->RT5 In this example, same traffic is traversing the RT7->RT4 link 3 times. Operationally this solution is very complex to manage. A network that starts with no segment protection, It may be ok to drop the traffic if some nodes have not been upgraded but causing congestion somewhere else would be difficult to debug. ------》[HZB] Traffic detour may exist in all local FRR mechanisms and is not unique to this solution, including TI-LFA.SR-TE Path protection etc， <SH> The problem I am indicating is not traffic detour, it is about bandwidth double booking on interfaces. The solution described in [draft-ietf-spring-segment-protection-sr-te-paths] also has this problem.for example you have mentioned, If using the solution of [ draft-ietf-spring-segment-protection-sr-te-paths], On failure of RT3, If the last calculated reachable path to RT3 is RT1->RT6->RT7->RT4->RT3, RT1 maintains the path of RT1->RT6->RT7->RT4->RT3 for forwarding during the Holdtimer period. Then, RT4 performs Proxy Forwarding and RT1->RT6->RT7->RT4->RT7->RT4->RT5. It also traverses the link 3 times from RT7 to RT4. I think extending the protocol is a much simpler way than slow route deletion and loop solving. <SH> This is incorrect example. Here the traffic is sent twice on RT7->RT4 interface twice even before the failure. This is problem with how SR-TE calculated the path and not a problem with procedures described in draft-ietf-spring-segment-protection-sr-te-paths ------》[HZB2] draft-ietf-spring-segment-protection-sr-te-paths mentioned： If the Node-SID or Prefix-SID becomes unreachable, the event and resulting forwarding changes should not communicated to the forwarding planes on all configured routers (including PLRs for the failed node) until the hold-timer expires. The traffic will continue to follow the previous path and get FRR protection on the PLR. On failure of RT3，RT1 detects the Link RT3-RT2, Link RT3-RT6 and Link RT3-RT7 failure first. RT1`s shorest Path to RT3 is RT1->RT6->RT7->RT4->RT3, And then RT1 detects the Link RT3-RT4 failure. The Node-Sid of RT3 become unreachable. RT1 will keep the previous path RT1->RT6->RT7->RT4->RT3. Packets are forwarded to RT4 for PLR, RT4 will send next segment RT7，RT7 will then send to RT5 via RT7->RT4->RT5. The path described in this case is exactly the same as the forwarding path described in your example（In both cases, RT4 is selected as the PLR, and the results are the same.） I don't know why you think one is 3 times and the other is 2 times. So, for draft-ietf-spring-segment-protection-sr-te-paths，Even if all nodes support this draft, it is possible that traversing the RT7->RT4 link 3 times. You actually gave an example of reacting [draft-ietf-spring-segment-protection-sr-te-paths] disadvantages. <SH> What you are describing in above text is a case when the link down events are reaching RT1 in a particular Order and one particular link down event is reaching very late on all the nodes on the path which is a corner case. There are already existing solutions such as spf-delay that can ensure most correlated events are clubbed together in one SPF. The local computations on RT1 can also be optimized to detect node down events and the previous paths to hold down. What you claim about fully upgraded network is not correct in this particular example is not true. When all the nodes are supporting context tables, RT6 will make sure to lookup next label and send to RT7. I don’t see any strong justification how proxy forwarding is improving the situation of partially upgraded network which it claims to be doing. 1. BSID solution draft-ietf-spring-segment-protection-sr-te-paths does not explicitly discuss the solution for BSIDs. Most of the BSID deployments use anycast based solution where same BSID is assigned on anycast nodes and BSID is always preceded by the anycast SID. Section 2.2 in draft-ietf-spring-segment-protection-sr-te-paths discusses this approach. draft-hu-spring-segment-routing-proxy-forwarding provides a protection solution for BSIDs when anycast is not in use. If WG is inclined to solve the BSID protection problem when anycast solution is not in use, I would prefer the Approach to be more aligned with draft-ietf-spring-segment-protection-sr-te-paths. I do not support Introducing completely different solution based on proxy forwarding which has other implications described in point 1. ------》[HZB]I don`t think that most of the BSID deployments use anycast based solution，Strict path control is required in most scenarios, and anycast is not introduced. If Bsid is not addressed, it will not be a complete protection solution. Rgds Shraddha Juniper Business Use Only From: spring spring-boun...@ietf.org<mailto:spring-boun...@ietf.org> On Behalf Of bruno.decra...@orange.com<mailto:bruno.decra...@orange.com> Sent: Thursday, January 13, 2022 3:49 PM To: SPRING WG <spring@ietf.org<mailto:spring@ietf.org>> Subject: [spring] WG adoption call - draft-hu-spring-segment-routing-proxy-forwarding [External Email. Be cautious of content] Dear WG, This message starts a 2 week WG adoption call, ending 27/01/2022, for draft-hu-spring-segment-routing-proxy-forwarding https://datatracker.ietf.org/doc/draft-hu-spring-segment-routing-proxy-forwarding/<https://urldefense.com/v3/__https:/datatracker.ietf.org/doc/draft-hu-spring-segment-routing-proxy-forwarding/__;!!NEt6yMaO-gk!TWaV4x51MCL2h93fiW-3XI8ElTsP963AWA5gjKCMU6g9E1WN0cRkqV6D5Qi50WbR$> After review of the document please indicate support (or not) for WG adoption of the document to the mailing list. Please also provide comments/reasons for your support (or lack thereof) as this is a stronger way to indicate your (non) support as this is not a vote. If you are willing to work on or review the document, please state this explicitly. This gives the chairs an indication of the energy level of people in the working group willing to work on the document. Thanks! 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