[spring] Deborah Brungard's Discuss on draft-ietf-spring-problem-statement-06: (with DISCUSS and COMMENT)
"Deborah Brungard" <db3546@att.com> Sun, 31 January 2016 23:11 UTC
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From: Deborah Brungard <db3546@att.com>
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Subject: [spring] Deborah Brungard's Discuss on draft-ietf-spring-problem-statement-06: (with DISCUSS and COMMENT)
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Deborah Brungard has entered the following ballot position for draft-ietf-spring-problem-statement-06: Discuss When responding, please keep the subject line intact and reply to all email addresses included in the To and CC lines. (Feel free to cut this introductory paragraph, however.) Please refer to https://www.ietf.org/iesg/statement/discuss-criteria.html for more information about IESG DISCUSS and COMMENT positions. The document, along with other ballot positions, can be found here: https://datatracker.ietf.org/doc/draft-ietf-spring-problem-statement/ ---------------------------------------------------------------------- DISCUSS: ---------------------------------------------------------------------- The main focus of my discuss are the disparaging comments on MPLS and RSVP-TE for the apparent purpose of justifying the need for SPRING. The statements in Section 3.3, paragraph 2, are not accurate. As an IETF document, even though Informational, it harms another IETF technology. This paragraph needs to be removed. Very disappointing to see this unfair comparison of centralized control vs. distributed control in an IETF document. ---------------------------------------------------------------------- COMMENT: ---------------------------------------------------------------------- As others commented, the document is missing the identification of key requirements, “MUST”. The Abstract’s last sentence and Section 3.1 say the objective is to address use cases where removal of signaling and path state in the core is a requirement. Yet, 3.1.1 and 3.2 only say it “SHOULD” work without the addition of a signaling protocol. If any requirement is a “MUST”, it would seem this requirement needs to be a “MUST”. There is no need to make statements that RSVP-TE is complex and not scalable to justify. Just say simply you do not want to use a distributed control plane for your problem. This is not the first time for this requirement. As for no need for state at transit nodes, it’s not quite true, as there probably is a need to map the SR “label” to a label stack instruction and a forwarding instruction. Hint, the “MUST” would be similar to MPLS-TP requirements [RFC5654], “SPRING MUST support the capability for network operation without the use of any control-plane protocols.” The interchangeability of the terms “SPRING” and “segment routing” are confusing. I think if you would clarify the control model, it may help with the definitions. Section 1: “allow optimal virtualization by putting policy state in the packet header” and “policy is completely virtualized away from midpoints and tail-ends” doesn’t parse. By definition, it’s not “virtual” if it’s in the packet header. Seems to be a marketing statement, not a technical requirement. Section 2: It seems the document is already defining the solution for IPv6 segment routing. It would help to say what is the actual requirement – packets should be forwarded transparently through a legacy v6 network? Identifiable by SPRING-capable devices? Section 3: These use cases appear to be defining desired capabilities for a controller, not SPRING. It would be helpful to clarify what are the requirements for the dataplane’s “simple support” e.g. section 3.2 on FRR appears to be requirements on the controller, not the dataplane. And 3.3.1.2.1 on a capacity planning process in the controller. Section 3.3 Traffic Engineering: While this is labelled Traffic Engineering, the examples are only on traffic placement. Only a subset of Traffic Engineering. The other key aspect of TE is resource reservation. The text should clarify and refer to traffic placement and not the general term “TE”. Section 3.3.1.1 are all load balancing examples – not “TE”. While valid and useful, should not confuse the reader that it is TE. Section 3.3.1.2.2 I don’t think everyone would agree that a stateful PCE is an SDN controller. I think there is some confusion, especially the next paragraph, on a controller vs. orchestrator. There’s a lot of marketing hype in this section, best would be to say something generic and what it is doing (technically) e.g. “centralized-based optimization” (next paragraph). The requirements in this section seem to be generic, not “SDN”. I don’t understand the last one, “no delay is introduced to programming the midpoints and tail-end along the path”. Compared to what? If a change, is there a change for traffic placement within the network? Before a change, there also is delay - the controller usually will sync with the current state of the network. This sounds marketing “highly responsive to change”. State the requirement for SPRING. Missing requirements: OAM, any requirements on limiting the increased headers and overall frame size?
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