Hi, This is the excerpt from the RFC 3784 " If a link is advertised with the maximum link metric (2^24 - 1), this link MUST NOT be considered during the normal SPF computation. This will allow advertisement of a link for purposes other than building the normal Shortest Path Tree. An example is a link that is available for traffic engineering, but not for hop-by-hop routing."
This same usecase applies to flex-algo and generic metric as well. Maximum link metric Implies the link is not available for use in flex-lago but can be used for other Purposes like SR-TE. Rgds Shraddha Juniper Business Use Only -----Original Message----- From: Mengxiao.Chen <[email protected]> Sent: Thursday, January 12, 2023 1:18 PM To: Shraddha Hegde <[email protected]>; [email protected] Subject: RE: [Lsr] FW: I-D Action: draft-ietf-lsr-flex-algo-bw-con-04.txt [External Email. Be cautious of content] Hi Shraddha, Thank you for replies. I think the case of Flex-Algo is different from normal SPF. Flex-Algo is used to compute paths based on constraints. The topology constraints include whether a link is considered for flex-algo calculation. And it is already realized by Node Participation, Admin Group and SRLG, as specified in draft-ietf-lsr-flex-algo. Could you explain the reason for defining additional Max-Generic-Metric? Thanks, Mengxiao -----Original Message----- From: Shraddha Hegde <[email protected]> Sent: Thursday, January 12, 2023 12:45 PM To: Mengxiao.Chen <[email protected]>; [email protected] Subject: RE: [Lsr] FW: I-D Action: draft-ietf-lsr-flex-algo-bw-con-04.txt Hi Chenmengxiao, Thanks for review and comments. Pls see inline [SH] for replies Juniper Business Use Only -----Original Message----- From: Chenmengxiao <[email protected]> Sent: Wednesday, January 11, 2023 8:26 AM To: Shraddha Hegde <[email protected]>; [email protected] Subject: RE: [Lsr] FW: I-D Action: draft-ietf-lsr-flex-algo-bw-con-04.txt [External Email. Be cautious of content] Hi Shraddha, In the new version, Generic Metric sub-TLV added "A metric value of 0xFFFFFFFF is considered as maximum link metric and a link having this metric MUST NOT be considered in SPF computation." With that I have two questions/suggestions: #1 Generic Metric sub-TLV may be used for different kinds of metric-type, maximum value can have different meanings. Besides, Admin Group rules can be used to exclude a link in Flex-Algo. Why must define a global unreachable value? [SH] RFC 3784 defined MAX-LINK-METRIC so that links can be advertised but not used for normal SPF computation. Same case applies here where links are not considered for flex-algo calculations but can be used for other reasons inside a flex-algo plane. #2 According to draft-ietf-lsr-flex-algo, I think it's better to use "Flex-Algorithm calculations" instead of "SPF computation". [SH]. Agree. Will update . Thanks, Mengxiao -----Original Message----- From: Lsr <[email protected]> On Behalf Of Shraddha Hegde Sent: Tuesday, January 10, 2023 12:43 PM To: [email protected] Subject: [Lsr] FW: I-D Action: draft-ietf-lsr-flex-algo-bw-con-04.txt WG, New version of the draft has been posted. Changes listed below. 1. Suggested codepoints in IANA section removed 2. Section 2.1 and 2.2 updated. Metric 0 is allowed. Added below sentence " Maximum link metric MUST NOT be used in SPF" 3. editorial changes. Pls review the draft. Rgds Shraddha Juniper Business Use Only -----Original Message----- From: Lsr <[email protected]> On Behalf Of [email protected] Sent: Tuesday, January 10, 2023 10:10 AM To: [email protected] Cc: [email protected] Subject: [Lsr] I-D Action: draft-ietf-lsr-flex-algo-bw-con-04.txt [External Email. Be cautious of content] A New Internet-Draft is available from the on-line Internet-Drafts directories. This draft is a work item of the Link State Routing WG of the IETF. Title : Flexible Algorithms: Bandwidth, Delay, Metrics and Constraints Authors : Shraddha Hegde William Britto A J Rajesh Shetty Bruno Decraene Peter Psenak Tony Li Filename : draft-ietf-lsr-flex-algo-bw-con-04.txt Pages : 29 Date : 2023-01-09 Abstract: Many networks configure the link metric relative to the link capacity. High bandwidth traffic gets routed as per the link capacity. Flexible algorithms provides mechanisms to create constraint based paths in IGP. This draft documents a generic metric type and set of bandwidth related constraints to be used in Flexible Algorithms. 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