Hi! I just entered a DISCUSS position related to draft-ietf-spring-segment-routing-mpls (see below). I believe that the issue needs to be solved in conjunction with the IGP extension drafts, so I’m copying the authors/shepherds/chairs here.
Thanks! Alvaro. On April 10, 2019 at 4:25:22 PM, Alvaro Retana via Datatracker ( nore...@ietf.org) wrote: ---------------------------------------------------------------------- DISCUSS: ---------------------------------------------------------------------- (1) This first point is a cross-document DISCUSS. In short, the assumptions in this document about what an MCC is responsible for are not in line with the corresponding IGP drafts for OSPF [1][2] and IS-IS [3]. This misalignment must be resolved before any of these documents are published. [Note: I'll start a thread with the corresponding WGS, Authors, Shepherds, Chairs and ADs. Let's please discuss this point there.] This document uses the following definition in §2: "We call "MPLS Control Plane Client (MCC)" any control plane entity installing forwarding entries in the MPLS data plane. IGPs with SR extensions...are examples of MCCs." The focus of the IGP drafts is on the transport of the SR information, and not on other functions (see below). Which component is responsible for what is the point that needs clarification -- either in this document, the IGP drafts, or both. These are some specific cases: (1.1) §2.4 (Mapping a SID Index to an MPLS label): "The following rules MUST be applied by the MCC when calculating the MPLS label value corresponding the SID index value "I"." There's nothing in the IGP extension documents that point at this set of rules, and only a passing reference in the OSPF documents about outgoing labels. (1.2) §2.5 (Incoming Label Collision) also assumes more functions from an MCC than what the IGP documents do. For example: "Within an MCC, apply tie-breaking rules to select one FEC only and assign the label to it." (1.3) §2.8 also expects work by the IGPs: "the MCC is responsible for downloading the correct label value to FIB"...in this case not just calculating the label, but installing it in the FIB. (1.4) §2.10.1: "The method by which the MCC on router "R0" determines that PUSH or CONTINUE operation must be applied using the SID "Si" is beyond the scope of this document. An example of a method to determine the SID "Si" for PUSH operation is the case where IS-IS [I-D.ietf-isis-segment-routing-extensions]..." Note that the IS-IS draft (or the OSPF ones, for that matter) don't talk about how to determine the operation -- if that is out of scope of this document, then where is it specified? (1.5) From §2: An implementation SHOULD check that an IGP node-SID is not associated with a prefix that is owned by more than one router within the same routing domain. If so, it SHOULD NOT use this Node-SID, MAY use another one if available, and SHOULD log an error. rfc8402 reads (§3.2): "An IGP Node-SID MUST NOT be associated with a prefix that is owned by more than one router within the same routing domain." The text above is not in line with that (MUST NOT vs SHOULD). Also, how can "SHOULD check" be Normatively enforced? Both sentences above seem to be trying to specify a behavior for the IGPs. [1] https://tools.ietf.org/html/draft-ietf-ospf-segment-routing-extensions [2] https://tools.ietf.org/html/draft-ietf-ospf-ospfv3-segment-routing-extensions [3] https://tools.ietf.org/html/draft-ietf-isis-segment-routing-extensions
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