Benjamin Kaduk has entered the following ballot position for draft-ietf-rtgwg-multihomed-prefix-lfa-08: No Objection
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-rtgwg-multihomed-prefix-lfa/ ---------------------------------------------------------------------- COMMENT: ---------------------------------------------------------------------- I was forced to make lots of inferences while reading this document, so it's pretty likely that some of my comments will not make sense because I misunderstood the technology. My apologies in advance, and please help me to become un-confused. I think part of this is because the document relies very heavily on prior knowledge, and could be avoided by sprinkling a few more words here and there, such as "downstream-paths-only (for micro-loop avoidance)" or "alternate neighbor N of S". I've tried to note some more cases in the section-by-section comments. The Abstract and Introduction sound like they should be attached to an Informational document; why is this going for PS? Section 1.1 SPF - Shortest Path First PDU Is the "PDU" really entirely silent in the acronym? Section 2 It might be nice to super-briefly reframe the situation, maybe: The scenario for LFA protection for MHPs involves protecting a node N in the path from source S to MHP prefix P, providing an alternate path subject to constraints on the distance metric, measured as the sum of the cost of the links traversed by the path. Perhaps also expand the inequality headers slightly, as "Link-Protection for PO_i to P is possible via N if:" Cost(X,P) - Cost of reaching the prefix P from prefix originating node X. Isn't it important to note that the Cost differs from a D_opt in that the Cost is only defined for what we essentially model here as a link and not a multi-link path? Section 3 Are these procedures supposed to terminate when the first LFA is found, or produce multiple LFAs as output? (Perhaps this is just an editorial nit, but "for each alternate neighbor N" and "a valid LFA" would then be a singular/plural mismatch", and perhaps the "select N as" steps in the various procedures as well. The phrase "If alternate neighbor N is also prefix-originator of P" confused me a fair amount -- the "also" makes me think that what N is a neighbor of should be the "primary" prefix-originator of P, i.e., PO_best, but text elsewhere in the document implies that N is a neighbor of *S*, to be used as the next-hop for forwarding to P. I guess the intended sense of the "also" could be more like "if, in addition to being a neighbor, N is also a prefix-originator of P", but as written it seems ambiguous to me. However, if N is not a prefix-originator of P, the computing router SHOULD evaluate one of the corresponding LFA inequalities, as Why is this a SHOULD? Section 3.1 In this scenario, E and F both are pre-failure optimal points of attachment and share the same primary next-hop. Hence, an implementation MAY compare the kind of protection A provides to F (link-and-node protection) with the kind of protection C provides to E (link protection) and inherit the better alternative to prefix P and here it is A. I find that this chunk makes more sense if I read it as "kind of protection A provides to E" (not F). Am I just confused? In this case, prefix P MUST inherit corresponding LFAs of each primary next-hop calculated for the router advertising the same respectively. Is this MUST a new requirement imposed by this specification or a restatement of something from (e.g.) RFC 5286? In summary, if there are multiple pre-failure points of attachment for a MHP and primary next-hop of a MHP is same as that of the primary next-hop of the router that was pre-failure optimal point of attachment, an implementation MAY provide a better protection to MHP without incurring any additional computation cost. I had a hard time understanding why this is the case, most likely because I don't have a clear picture about what the reference point is for computational cost (that this is not "additional" to). Section 4.2.1 This procedure is not super-well-defined if a cost type other than 1 or 2 is encountered. 5. If route type (type 5/type 7) 5a. If route type is same, check route p-bit, forwarding address field for routes from both ASBRs match. [...] nit: "check if the route p-bit and the forwarding address field for" Section 4.2.1.2 If there are multiple ASBRs not pruned via rules defined in Section 4.2.1.1, [...] nit: I wouldn't exactly say that the rules are *defined* in 4.2.1.1, rather that they are "described in" or "referred to by" it. Section 4.2.2.1 Similarly to a previous comment, if we started out with "A neighbor N of S is a valid LFA to P under the named conditions when the corresponding inequality holds:", that would seem to help readability a lot. Section 5.2 In Multi Topology (MT) IGP deployments, for each MT ID, a separate shortest path tree (SPT) is built with topology specific adjacencies, the LFA principles laid out in [RFC5286] are actually applicable for MT IS-IS [RFC5120] LFA SPF. [...] nit: I think this is formally a comma splice as written, and would be better by adding "so" after the last comma, and maybe expanding to "so the LFA principles laid out in [RFC5286] are actually applicable on a per-MT-ID basis for MT IS-IS [RFC5120] LFA SPF." Section 9 I don't see any new security considerations to mention here, but would suggest a rewording of the current text for readability: The existing OSPF security considerations continue to apply, as do the recommended manual key management mechanisms specified in [RFC7474]. The existing security considerations for IS-IS also continue to apply, as specified in [RFC5304] and [RFC5310] and extended by [RFC7645] for KARP. This document does not change any of the discussed protocol specifications [RFC1195] [RFC5120] [RFC2328] [RFC5838], and the security considerations of the LFA base specification [RFC5286] therefore continue to apply. _______________________________________________ rtgwg mailing list [email protected] https://www.ietf.org/mailman/listinfo/rtgwg
