Re: [Lsr] WG Adoption Call for "IGP Flexible Algorithms (Flex-Algorithm) In IP Networks" - draft-bonica-lsr-ip-flexalgo-01

Aijun Wang <> Thu, 03 December 2020 01:31 UTC

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From: "Aijun Wang" <>
To: "'Acee Lindem \(acee\)'" <>, "'lsr'" <>
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Date: Thu, 3 Dec 2020 09:31:32 +0800
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Subject: Re: [Lsr] WG Adoption Call for "IGP Flexible Algorithms (Flex-Algorithm) In IP Networks" - draft-bonica-lsr-ip-flexalgo-01
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Hi, authors:


Want to confirm one thing:

Does the mechanism described in this draft support the automatic fallback from “flex algorithm” to the “traditional least-cost algorithm”?  

That is to say, can one prefix exists both in the “flex algorithm” table and “traditional least-cost algorithm” table, the router prefer to forwarding the packet based on the former table, and if not hit, then lookup the latter table?


>From the context of the document, the answer seems not, or even on the contrary?

In cases where a prefix advertisement is received in both a IPv4

   Prefix Reachability TLV and an IPv4 Algorithm Prefix Reachability

   TLV, the IPv4 Prefix Reachability advertisement MUST be preferred

   when installing entries in the forwarding plane.


If so, what the value to deploy such flexible algorithm within the network? From my POV, the reason that we want to deploy such mechanism is that we want to differentiate the path(result of flex algorithm) of some traffic from that(result of traditional least-cost algorithm) of most other normal traffic.


Best Regards


Aijun Wang

China Telecom


From: <> On Behalf Of Acee Lindem (acee)
Sent: Wednesday, December 2, 2020 5:13 AM
To: lsr <>
Subject: [Lsr] WG Adoption Call for "IGP Flexible Algorithms (Flex-Algorithm) In IP Networks" - draft-bonica-lsr-ip-flexalgo-01


This IP Flex Algorithm draft generated quite a bit of discussion on use cases and deployment prior to IETF 109 and there was generally support for WG adoption. This begins a two week WG adoption call. Please indicate your support or objection to WG adoption on this list prior to 12:00 AM UTC on December 16th, 2020. Also, review comments are certainly welcome.