Hi, Xiaohu, Please see inline.
— Carlos Pignataro, [email protected]<mailto:[email protected]> “Sometimes I use big words that I do not fully understand, to make myself sound more photosynthesis." On Nov 9, 2016, at 11:29 PM, Xuxiaohu <[email protected]<mailto:[email protected]>> wrote: Hi Carlos, Thanks for your comments. Please see my response inline. 发件人: OSPF [mailto:[email protected]] 代表 Carlos Pignataro (cpignata) 发送时间: 2016年11月8日 23:20 收件人: Bruno Decraene 抄送: OSPF WG List 主题: Re: [OSPF] WG Last Call for "Signalling ELC using OSPF" Jumping a bit mid-thread, but with somewhat similar or related comments. Summary: I am concerned with the lack of precision in the definitions and usage on these set of documents. Acee, if this document needs to depend on Section 4 of draft-ietf-mpls-spring-entropy-label-04.txt, then the issue is compounded. I believe draft-ietf-mpls-spring-entropy-label-04has its own set of problems (for example, placing EL/ELI independent of whether the underlying Label is for a Node SID or a Segment SID is not optimum). So the main question is: Is draft-ietf-ospf-mpls-elc-03 to be treated independently form draft-ietf-mpls-spring-entropy-label-04? That is a fundamental question for advancing and reviewing this/these doc(s). We have the advertisement of a capability — what is it used for? Is it the right variable to advertise (based on the application using it)? [Xiaohu] draft-ietf-ospf-mpls-elc-03 defines an approach of advertising the RLDC of an LSR via OSPF. The definition of the RLDC is described in the following text (i.e., each LSR's capability of reading the maximum label stack depth). To me “LSR's capability of reading the maximum label stack depth” does not mean “the value of LSEs that an LSR can read in an MPLS label stack”... As for how to use this capability, it’s not limited by the draft although one use case (i.e., the application as described in Section 4 of draft-ietf-mpls-spring-entropy-label-04.txt) is mentioned in this draft. Specifically, I think that RLDC is largely underspecified. The doc says: " it would be useful for ingress LSRs to know each LSR's capability of reading the maximum label stack deepth. This capability, referred to as Readable Label Deepth Capability (RLDC) “ That definition simple does not make sense. And it does not explain the applicability (A, b, c, d). [Xiaohu]Could you speak more specifically? Is the definition of the RLDC (i.e., what is the capability of reading the maximum label stack depth) itself not clear enough? It is not fully clear to me. Maybe it is just me. What is the “capability of reading the maximum label stack deepth”? A capability to me is a binary state. Yes, capable, not capable. What is the “maximum label stack depth”? But it’s not just grammar. From the definition in RFC 3031: https://tools.ietf.org/html/rfc3031#section-3.9 If a packet's label stack is of depth m, we refer to the label at the bottom of the stack as the level 1 label, to the label above it (if such exists) as the level 2 label, and to the label at the top of the stack as the level m label. Which means the bottom is label 1, the minimum not the maximum. If so, could you please suggestion any more specific text? Or the applicability of the RLDC not clear enough? If so, we co-authors currently only think about one use case of this RLDC that is described in Section 4 of draft-ietf-mpls-spring-entropy-label-04.txt) , please feel free to tell us if you find any other use cases of this RLDC. No, Xiaohu. That thinking is the other way around. You are defining something independent of the use case. Your definition is generic and outside the use of SPRING. It is independent of SR. And yes, the applicability is not clear enough — since it is beyond (and independent of) SR, but dependent of LB techniques, maybe? Then the doc continues: “ Readable Label Deepth Capability (RLDC) can be used by ingress LSRs to determine whether it's necessary to insert an EL for a given LSP tunnel in the case where there has already been at least one EL in the label stack [I-D.ietf-mpls-spring-entropy-label] . " So this only is useful when there’s an EL (I assume ELI/EL pair) already? [Xiaohu] In the EL insertion use case, yes, your understand is correct. What’s another use case? And is “[I-D.ietf-mpls-spring-entropy-label]” normative? [Xiaohu] Currently yes, if it’s widely believed that this reference should be informational, it can be moved to the informational reference section. It is informational now!!! Should it be Normative? Overall, I think a WGLC is premature, since some basics are not well covered. Is it RLD or RLDC? And what exactly is a “Readable Label Deepth Capability (RLDC)” The capability to do what? Is this a Capability or a scalar? [Xiaohu] RLDC (Readable Label Deeth Capability) means a given LSR's capability of reading the maximum label stack depth. What is “the maximum label stack depth”? If it’s widely believed that “RLD” is more suitable than “RLDC” from the expression perspective, it’s fine to make a change. I’m not sure what’s widely believed. What I believe is that calling something RLD in some place, and RLDC in others is not useful. Further, I think that the way this is defined is a per-advertisement value. However, in your other draft on mpls-spring-EL, you use the same definition to mean something else, to be per path or per network. Which one is it? Another point comment — although I think this needs a thorough review before WGLC. The doc says: Of course, even it has been determined that it's neccessary to insert an EL for a given LSP tunnel, if the egress LSR of that LSP tunnel has not yet indicated that it can process ELs for that tunnel, the ingress LSR MUST NOT include an entropy label for that tunnel as well. This is good and consistent with RFC 6790: c. X MUST NOT include an entropy label for a given tunnel unless the egress LSR Y has indicated that it can process entropy labels for that tunnel. So it’s better to point to it instead of re-MUST NOT independently. [Xiaohu] Good suggestion. Will fix it. But, what is the egress of a tunnel in this context? Not the final egress, but the SID egress. ? [Xiaohu] IMHO, the egress of an LSP tunnel is clear enough and easy to understand. In contrast, what’s the mean of SID egress, could you please help point to a reference for this term defincation? That’s my point — most terms are not defined. Thanks, — Carlos. Best regards, Xiaohu Thanks, — Carlos Pignataro, [email protected]<mailto:[email protected]> “Sometimes I use big words that I do not fully understand, to make myself sound more photosynthesis." On Nov 8, 2016, at 6:15 AM, [email protected]<mailto:[email protected]> wrote: Hi Acee, Thanks for your reply. Please see inline [Bruno] From: Acee Lindem (acee) [mailto:[email protected]] Sent: Tuesday, November 08, 2016 2:27 AM To: DECRAENE Bruno IMT/OLN; OSPF WG List Subject: Re: [OSPF] WG Last Call for "Signalling ELC using OSPF" Hi Bruno, From: Bruno Decraene <[email protected]<mailto:[email protected]>> Date: Monday, November 7, 2016 at 6:43 AM To: Acee Lindem <[email protected]<mailto:[email protected]>>, OSPF WG List <[email protected]<mailto:[email protected]>> Subject: RE: [OSPF] WG Last Call for "Signalling ELC using OSPF" Hi authors, all, Please find below some comments on the RLDC definition. 1) I’d like to see a more specific definition of RLDC. e.g. load-balancing hashing could be done based on (hashing): -a- a (stack of) N “regular” MPLS labels (i.e. there is no ELI in this stack) -b- the (IP) header below the stack of N labels -c- the EL label in the stack of N labels (i.e. there is one ELI in this stack) I’d like the specification to be clear on the applicability of the RLDC. Does it apply on these 3 cases, on only a subset? Personally, I’d like at least a and c be in scope of the RLDC definition, such that an ingress with limited push capability could have enough information to decide that it could avoid pushing an ELI,EL pair if the stack of MPLS labels that it pushes has enough entropy within the first RLDC labels. I think that the signaling document should reference section 4 of https://www.ietf.org/id/draft-ietf-mpls-spring-entropy-label-04.txt. However, I don’t think -b- is covered there. [Bruno] The above section 4 has indeed more details, but I’m not certain that the definition is clear enough for everyone to agree on which “a”, “b”, “c” cases are covered by the RLDC advertisement. My reading would be that “a” and “c” are covered, not “b”. Reading your email, I’d say that you have the same understanding. But it bothers me that one of the authors has a different understanding. Also draft-ietf-mpls-spring-entropy-label-04.txt is an informational document, so I’m not sure how much it would qualify to be a normative definition of what draft-ietf-ospf-mpls-elc advertise. Thanks, Regards, -- Bruno 2) Current text seems to limit the use of the RLDC to the insertion of a _second_ EL. Why is the RLD not applicable to the first EL? §1. Introduction “This capability, referred to as Readable Label Deepth Capability (RLDC) can be used by ingress LSRs to determine whether it's necessary to insert an EL for a given LSP tunnel in the case where there has already been at least one EL in the label stack [I-D.ietf-mpls-spring-entropy-label<https://tools.ietf.org/html/draft-ietf-ospf-mpls-elc-03#ref-I-D.ietf-mpls-spring-entropy-label>]” §6 Usage and Applicability “The RLDC is used by ingress LSRs to determine whether it's necessary to insert an EL for a given LSP tunnel in the case where there has already been at least one EL in the label stack. » I think that this is an unnecessary restriction of the RLDC usage. Indeed, an ingress with a limited capability in term of label push, could be forced to push a single EL label. It should be able to use the RLDC info in order to choose the best location for the EL, even if it pushes a single one. But both sentences seems to restrict RLDC usage for the additional EL push, not the first one. I would tend to agree. Thanks, Acee Thanks, Regards, --Bruno From: OSPF [mailto:[email protected]] On Behalf Of Acee Lindem (acee) Sent: Saturday, November 05, 2016 5:46 PM To: OSPF WG List Subject: [OSPF] WG Last Call for "Signalling ELC using OSPF" This begins the WG last call for "Signalling ELC using OSPF”, https://www.ietf.org/id/draft-ietf-ospf-mpls-elc-03.txt. Please review the document and send comments to this list prior to Nov 27th, 2016. Due to the IETF week, the last call period is going to be 3 weeks rather than usual 2 weeks. Thanks, Acee _________________________________________________________________________________________________________________________ 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. 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