Fwd: [OPS-DIR] Opsdir early review of draft-ietf-rtgwg-segment-routing-ti-lfa-12
Gyan Mishra <hayabusagsm@gmail.com> Mon, 18 December 2023 07:05 UTC
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From: Gyan Mishra <hayabusagsm@gmail.com>
Date: Mon, 18 Dec 2023 02:05:11 -0500
Message-ID: <CABNhwV0G3NfiqOSiRzk-AP53cVSWQOLka5bC7KGmvaNBq9M1Xw@mail.gmail.com>
Subject: Fwd: [OPS-DIR] Opsdir early review of draft-ietf-rtgwg-segment-routing-ti-lfa-12
To: Alexander Vainshtein <Alexander.Vainshtein@rbbn.com>, Bruno Decraene <bruno.decraene@orange.com>, Jeff Tantsura <jefftant.ietf@gmail.com>, RTGWG <rtgwg@ietf.org>, Routing WG <rtgwg-chairs@ietf.org>, Stewart Bryant <stewart.bryant@gmail.com>, "Voyer, Daniel" <daniel.voyer@bell.ca>, Yingzhen Qu <yingzhen.ietf@gmail.com>, draft-ietf-rtgwg-segment-routing-ti-lfa@ietf.org
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Hi Yingzhen & Jeff I completed the updated OPSDIR Review of TO-LFA draft and changed status from “serious issues” to “Ready”. Thank you <http://www.verizon.com/> *Gyan Mishra* *Network Solutions A**rchitect * *Email gyan.s.mishra@verizon.com <gyan.s.mishra@verizon.com>* *M 301 502-1347* ---------- Forwarded message --------- From: Gyan Mishra via Datatracker <noreply@ietf.org> Date: Mon, Dec 18, 2023 at 2:00 AM Subject: [OPS-DIR] Opsdir early review of draft-ietf-rtgwg-segment-routing-ti-lfa-12 To: <ops-dir@ietf.org> CC: <draft-ietf-rtgwg-segment-routing-ti-lfa.all@ietf.org>, <rtgwg@ietf.org> Reviewer: Gyan Mishra Review result: Ready I have reviewed version 12 and am updating my initial review of TI-LFA in August which this review. Summary: Based on revision 12 review, the draft is ready for publication. Review details: IETF 118 side meeting discussion summary: We had a very productive discussion during the side meeting, and the review comments and open issues have been addressed. Outcome of the discussion: It’s important for the draft to clarify that with ti-lfa, when IGP starts to reconverge, there is still a possibility for micro-loops. So customers should be advised to deploy some micro-loop protection mechanisms to prevent traffic loss. Action items for authors of the ti-lfa draft: • To include text from RFC7490 second paragraph of section 10 - done • To include the text summary in the email thread - done • Change the text in section 6.1 from node to link - done Next steps: After the draft is updated to address the open issues which was completed with version 12, Gyan Mishra will update the OPS Directorate review, and the RTGWG WG Chairs will start the WGLC of this draft. Draft updates from v11 to v12 below: When the network reconverges, micro-loops [RFC5715] can form due to transient inconsistencies in the forwarding tables of different routers. If it is determined that micro-loops are a significant issue in the deployment, then a suitable loop-free convergence method, such as one of those described in [RFC5715], [RFC6976], [RFC8333], or [I-D.bashandy-rtgwg-segment-routing-uloop] should be implemented. TI-LFA is a local operation applied by the PLR when it detects failure of one of its local links. As such, it does not affect: * Micro-loops that appear - or do not appear – as part of the distributed IGP convergence [RFC5715] on the paths to the destination that do not pass thru TI-LFA paths: - As explained in [RFC5714], such micro-loops may result in the traffic not reaching the PLR and therefore not following TI-LFA paths. - Segment Routing may be used for prevention of such micro-loops as described in [I-D.bashandy-rtgwg-segment-routing-uloop]. * Micro-loops that appear – or do not appear - when the failed link is repaired. TI-LFA paths are loop-free. What’s more, they follow the post- convergence paths, and, therefore, not subject to micro-loops due to difference in the IGP convergence times of the nodes thru which they pass. TI-LFA paths are applied from the moment the PLR detects failure of a local link and until IGP convergence at the PLR is completed. Therefore, early (relative to the other nodes) IGP convergence at the PLR and the consecutive ”early” release of TI-LFA paths may cause micro-loops, especially if these paths have been computed using the methods described in Section Section 6.2, Section 6.3, or Section 6.4 of the draft. One of the possible ways to prevent such micro-loops is local convergence delay ([RFC8333]). TI-LFA procedures are complementary to application of any micro-loop avoidance procedures in the case of link or node failure: * Link or node failure requires some urgent action to restore the traffic that passed thru the failed resource. TI-LFA paths are pre-computed and pre-installed and therefore suitable for urgent recovery * The paths used in the micro-loop avoidance procedures typically cannot be pre-computed. 6.1. FRR path using a direct neighbor When a direct neighbor is in P(S,X) and Q(D,x) and the link to that direct neighbor is on the post-convergence path, the outgoing interface is set to that neighbor and the repair segment list SHOULD be empty. This is comparable to a post-convergence LFA FRR repair. Major issues: None Minor issues: Stewart Bryant pick up something that was agreed but was not included in this summary: we agreed to remove the reference to draft-bashandy in order to make the discussion on uloop prevention technology neutral. So the TI-LFA draft even though it has loop preventing mechanisms that can possibly work independently of a separate uLoop avoidance mechanism, that there are cases as we both pointed out that uLoops can form, in those cases for further convergence time optimization a separate uLoop prevention mechanism maybe necessary. So in that case the current reference to the uLoop avoidance draft could apply. However, I do think the uLoop draft needs a lot of work particularly section 3 and is an I-D. So I agree we need to remove any references to the uLoop draft and stating that a separate from TI-LFAs uLoop prevention technology is necessary. The uLoop draft as it exists would be the appropriate draft to be referenced but unfortunately it’s not ready so I don’t think we should reference it. Nits: None _______________________________________________ OPS-DIR mailing list OPS-DIR@ietf.org https://www.ietf.org/mailman/listinfo/ops-dir
- Opsdir early review of draft-ietf-rtgwg-segment-r… Gyan Mishra via Datatracker
- Fwd: [OPS-DIR] Opsdir early review of draft-ietf-… Gyan Mishra
- Re: [OPS-DIR] Opsdir early review of draft-ietf-r… Yingzhen Qu
- Re: [OPS-DIR] Opsdir early review of draft-ietf-r… Gyan Mishra
- Re: Fwd: [OPS-DIR] Opsdir early review of draft-i… Ahmed Bashandy
- Re: Fwd: [OPS-DIR] Opsdir early review of draft-i… Gyan Mishra
- Re: Fwd: [OPS-DIR] Opsdir early review of draft-i… Ahmed Bashandy
- Re: Fwd: [OPS-DIR] Opsdir early review of draft-i… Gyan Mishra
- Re: Fwd: [OPS-DIR] Opsdir early review of draft-i… Ahmed Bashandy