Hi Chris, Thanks for the addition. Please see inline some comments. [Bruno]
Thanks, Regards, Bruno From: rtgwg [mailto:[email protected]] On Behalf Of Chris Bowers Sent: Wednesday, April 01, 2015 3:10 AM To: Anil Kumar S N (VRP Network BL); Alia Atlas; Robert Kebler; [email protected]; [email protected]; [email protected]; [email protected]; [email protected] Subject: RE: draft-ietf-rtgwg-mrt-frr-architecture-05.txt Anil, Thanks for your input and proposed text. I added the text below (which is a slightly modified version of your proposed text) to the most recent version which is being maintained at: https://github.com/cbowers/draft-ietf-rtgwg-mrt-frr-architecture Tell me if you are OK with the final sentence that I added as well, or you can propose some other wording. Thanks, Chris TI-LFA: Topology Independent Loop-free Alternate Fast Re-route (TI-LFA) [I-D.francois-spring-segment-routing-ti-lfa] aims to provide link and node protection of node and adjacency segments within the Segment Routing (SR) framework. It has improved coverage over LFA and Remote LFA for link and node protection and also guarantees complete coverage. [Bruno] The last sentence could probably be shortened by only keeping the last part. "It guarantees complete coverage" The trade-off of looping traffic to improve coverage is still made. [Bruno] I'm not sure to see what you mean. Contrary to LFA & RLFA, I don't think TI-LFA makes such tradeoff. The computation required is quite high with added complexity. [Bruno] As in the RLFA description you have made the distinction between link and node protection, it would be fair to do the same for TI-LFA. (Link protection computation is much easier) TI-LFA is supported only for the MPLS data plane due to the requirement for the PLR to impose an MPLS label stack on link failure. On certain topologies the label stack size can grow significantly based on repair path. [Bruno] I agree for node failure. For link failure, this is more debatable as compared to RLFA it may require at most 1 additional label. (assuming symmetric link costs) Note that TI-LFA requires shortest path forwarding based on SR Node-SIDs, as opposed to LDP labels, in order to construct label stacks for backups paths without relying on a large number of targeted LDP sessions to learn remote FEC-label bindings. [Bruno] It also requires Adj-SID (in order to provide 100% coverage). From: Anil Kumar S N (VRP Network BL) [mailto:[email protected]] Sent: Saturday, March 28, 2015 8:10 AM To: Alia Atlas; Robert Kebler; Chris Bowers; [email protected]<mailto:[email protected]>; [email protected]<mailto:[email protected]>; [email protected]<mailto:[email protected]>; [email protected]<mailto:[email protected]>; [email protected]<mailto:[email protected]> Subject: draft-ietf-rtgwg-mrt-frr-architecture-05.txt Hi Authors, In "comparison of IP/LDP FRR Methods" section of the document , I feel we should add comparison with TI-LFA (draft-francois-spring-segment-routing-ti-lfa-01) where TI-LFA approach achieves guaranteed coverage against link or node failure, in any IGP network, relying on the flexibility of SR. This will give readers better picture and enables them with more information so that they can choose MRT if they feel it suites their requirement better; compared to IT-LFA... Changes : 1. Introduction : Other existing or proposed solutions are partial solutions or have significant issues, as described below. Summary Comparison of IP/LDP FRR Methods +---------+-------------+-------------+-----------------------------+ | Method | Coverage | Alternate | Computation (in SPFs) | | | | Looping? | | +---------+-------------+-------------+-----------------------------+ | MRT-FRR | 100% | None | less than 3 | | | Link/Node | | | | | | | | | LFA | Partial | Possible | per neighbor | | | Link/Node | | | | | | | | | Remote | Partial | Possible | per neighbor (link) or | | LFA | Link/Node | | neighbor's neighbor (node) | | | | | | | Not-Via | 100% | None | per link and node | | | Link/Node | | | | | | | | | TI-LFA | 100% | Possible | per neighbor (link) or | | | Link/Node | | neighbor's neighbor (node) | | | | | | +---------+-------------+-------------+-----------------------------+ Table 1 TI-LFA: Topology Independent Loop-free Alternate Fast Re-route (TI-LFA), aimed at providing link and node protection of node and adjacency segments within the Segment Routing (SR) framework [draft-francois-spring-segment-routing-ti-lfa-01]. Has improved coverage over LFAs and Remote LFA for link and node protection and also guarantees complete coverage. The trade-off of looping traffic to improve coverage is still made. The computation required is quite high with added complexity. TI-LFA is supported only MPLS data plane with a requirement to carry additional MPLS label stack on the link failure; on certain topologies stack size can grow significantly based repair path. Thanks & Regards Anil S N "Be liberal in what you accept, and conservative in what you send" - Jon Postel _________________________________________________________________________________________________________________________ Ce message et ses pieces jointes peuvent contenir des informations confidentielles ou privilegiees et ne doivent donc pas etre diffuses, exploites ou copies sans autorisation. Si vous avez recu ce message par erreur, veuillez le signaler a l'expediteur et le detruire ainsi que les pieces jointes. 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