Benjamin -
Thanx for your review. Responses inline. > -----Original Message----- > From: Benjamin Kaduk via Datatracker <nore...@ietf.org> > Sent: Thursday, June 11, 2020 12:42 AM > To: The IESG <i...@ietf.org> > Cc: draft-ietf-isis-te-...@ietf.org; lsr-cha...@ietf.org; lsr@ietf.org; Acee > Lindem (acee) <a...@cisco.com>; aretana.i...@gmail.com; Acee Lindem > (acee) <a...@cisco.com> > Subject: Benjamin Kaduk's Discuss on draft-ietf-isis-te-app-14: (with DISCUSS > and COMMENT) > > Benjamin Kaduk has entered the following ballot position for > draft-ietf-isis-te-app-14: 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-isis-te-app/ > > > > ---------------------------------------------------------------------- > DISCUSS: > ---------------------------------------------------------------------- > > My apologies if this is super-obvious and I'm just missing it ... but > Section 4.3 dictates that part of the value for the application-specific > SRLG TLV is a "Neighbor System-ID + pseudo-node ID (7 octets)". Where > are these defined? (We don't exactly say that we're reusing the structure > from, e.g., TLV 138, which I note refers to the seventh octet as > "pseudonode number", not "pseudo-node ID". Similarly for the > interpretation of the SRLG value(s). Do we just need to reference that > we're reusing the encoding from RFC 5307 (or similar) or are some > changes needed? > [Les:] “system ID” and “pseudo-node ID” derive from the IS-IS base specification [ISO 19589] > > ---------------------------------------------------------------------- > COMMENT: > ---------------------------------------------------------------------- > > What is the scope over which the user-defined application bits are > defined/allocated? [Les:] Sorry – I do not understand this question. > > And, a general question, just to check my understanding: if I do need to > specify different values of a given attribute for different > applications, I do that by putting multiple copies of the new sub-TLV in > TLV 22/23/etc., with the flags set according to which application the > contained attributes apply to? (Mostly I ask because I forget what the > rules are for having multiple instances of a given TLV/sub-TLV as > siblings in the same container.) > [Les:] You are correct. Whether multiple occurrences of the same sub-TLV is allowed is codepoint specific. Section 4.2 states: “Multiple Application Specific Link Attribute sub-TLVs for the same link MAY be advertised.” > Section 3.1 > > Maybe mention (again, I know) that this is only the subset of sub-TLVs > that are used for RSVP-TE? [Les:] The point of Section 3.1 is to list the legacy sub-TLVs which are relevant to this draft. There are other sub-TLVs defined in https://www.iana.org/assignments/isis-tlv-codepoints/isis-tlv-codepoints.xhtml#isis-tlv-codepoints-22-23-25-141-222-223 which are not relevant – but categorizing them as “not used by RSVP-TE” wouldn’t be completely accurate. For example, endpoint addresses (codepoints 6,8,12,13) are quite relevant to RSVP-TE as they are required to uniquely identify the link – but they aren’t in the set of sub-sub-TLVs being defined. > > Section 4.2 > > When the L-flag is set in the Application Identifier Bit Mask, all of > the applications specified in the bit mask MUST use the legacy > advertisements for the corresponding link found in TLVs 22, 23, 25, > 141, 222, and 223 or TLV 138 or TLV 139 as appropriate. Link > > nit(?): is this "found in sub-TLVs of TLVs 22, [...]"? [Les:] The top level TLVs are the containers in which link advertisements are present. A given link advertisement consists of the fixed portion of the TLV and a set of sub-TLVs. I think the existing text is correct. > > attribute sub-sub-TLVs for the corresponding link attributes MUST NOT > be advertised for the set of applications specified in the Standard/ > User Application Identifier Bit Masks and all such advertisements > MUST be ignored on receipt. > > Does this apply to just the (sub-)TLV with the L-flag set, or to other > instances of that (sub-)TLV as well? > [Les:] The scope is the set of sub-TLVs associated with the same link and the same application(s). > For a given application, the setting of the L-flag MUST be the same > in all sub-TLVs for a given link. In cases where this constraint is > violated, the L-flag MUST be considered set for this application. > > editorial: I suggest "the L-flag MUST be considered set for this > application for all sub-TLVs on the link in question". > [Les:] This seems redundant given the first sentence of the paragraph. ?? Note that if L-flag is set, no link attribute advertisements are permitted in the sub-TLV – so there is no reason to have multiple sub-TLVs for the same link/application in such a case. > If link attributes are advertised associated with zero length > Application Identifier Bit Masks for both standard applications and > user defined applications, then any Standard Application and/or any > > Do we need to talk about conflicts if there are multiple such sub-TLVs > for the link in question (that contain different values in the > sub-sub-TLV(s))? > [Les:] An earlier paragraph discusses conflicts and states: “In cases where conflicting values for the same application/attribute/link are advertised all the conflicting values MUST be ignored by the specified application.” I think that covers the “any application” case as well. > User Defined Application is permitted to use that set of link > attributes so long as there is not another set of attributes > advertised on that same link which is associated with a non-zero > length Application Identifier Bit Mask with a matching Application > Identifier Bit set. > > nit: this phrasing of "matching Application Identifier Bit set" does not > seem as clear as it could be that the bit for the application in > question is what's checked (though I have a hard time believing that > someone would accidentally misinterpret the meaning). > [Les:] I also have trouble seeing how this could be misinterpreted. Do you have a suggestion? > the link attribute sub-sub-TLV code points. This document defines a > sub-sub-TLV for each of the existing sub-TLVs listed in Section 3.1 > except as noted below. The format of the sub-sub-TLVs matches the > > Just to check that I'm matching things up properly: this leaves the only > attributes that do not have some form of exception noted as > administrative group, extended administrative group, and TE default > metric? > [Les:] The points being made in Sections 4.2.x are: 1)Maximum Bandwidth is not application specific 2)Reserved/Unreserved bandwidth are RSVP-TE specific 3)Extended TE Metrics MAY be application specific, but there are challenges in doing application specific performance measurement Sooo, you are following along quite well, but in the case of Extended TE Metrics I would not use the term “exception”. > Section 4.2.1 > > Maximum link bandwidth is an application independent attribute of the > link. When advertised using the Application Specific Link Attributes > sub-TLV, multiple values for the same link MUST NOT be advertised. > This can be accomplished most efficiently by having a single > advertisement for a given link where the Application Identifier Bit > Mask identifies all the applications which are making use of the > value for that link. > > If I want the same maximum link bandwidth to apply to all applications, > couldn't I just put it in a sub-TLV with both SABM and UDABM length of > zero? (Is this somehow less efficient than setting all the bits for the > applications making use of the value?) Section 4.2.3 seems to discuss > using the zero-length bit mask option in the context of TE metrics... > (I do note the note at the end of Section 5 about the "any application" > encoding leaving ambiguous whether an application is enabled, but I > don't see how this consideration differs between maximum link bandwidth > and extended TE metrics.) > [Les:] You are correct. I have added: “It is also possible to advertise a single advertisement with zero length SABM and UDABM so long as the constraints discussed in Section 4.2 and Section 6.2 are acceptable.” > Section 4.2.2 > > Maximum Reservable Link Bandwidth and Unreserved Bandwidth are > attributes specific to RSVP-TE. When advertised using the > Application Specific Link Attributes sub-TLV, bits other than the > RSVP-TE (R-bit) MUST NOT be set in the Application Identifier Bit > > Just to confirm: we find the risk of some future application that also > wants to do reservation-like things sufficiently low that we're okay > with preventing it from using these attributes? [Les:] It would require a definition of an alternative RSVP protocol. If/when that occurs a revision to this restriction could be specified. > > Section 4.3 > > What are the semantics when I specify more than one link identifier > sub-TLV? They are all supposed to identify the same link, and in some > case might be needed to disambiguate if there are (e.g.) multiple links > to the same neighbor? > [Les:] It might be useful to include both IPv4 and IPv6 addresses. It does not seem useful to include Link Identifiers and IPvX addreesses – though not in and of itself harmful. I have added: “Multiple occurrences of the same identifier type MUST NOT be present.” > Section 5 > > In the case of SRTE, advertisement of application specific link > attributes does not indicate enablement of SRTE on that link. The > > Is the SRTE specification sufficiently final that we're comfortable > enshrining in a (different) RFC this property of it? [Les:] This property exists – largely because existing RSVP-TE specifications never defined a standard definition of enablement. Implementations therefore had to come up with an ad hoc solution. We are simply reflecting the deployed reality. > I note that we > only list draft-ietf-spring-segment-routing-policy as an informative > reference, so it's entirely possible that this document will be > published as an RFC before that document is done. > [Les:] My understanding of this oft discussed point is that the choice of Informative vs Normative Reference depends on the relationship between the two documents – not the current document status of the referenced document. In this case nothing in this draft depends on content in the SR Policy draft, but it is informative in providing context for the content of this draft. ?? > Section 6.1 > > the writing of this document. Therefore, such applications have been > deployed using the legacy advertisements. The Standard Applications > defined in this document may continue to use legacy advertisements > for a given link so long as at least one of the following conditions > is true: > > nit(?): do we want to say something like "may safely continue" or "may > continue to use without ill effect"? > [Les:] There are limitations (discussed immediately below in the draft) to when this can be done. I am comfortable with the current text. > Section 6.3.2 > > advertisements as defined in this document. Attributes for > applications other than RSVP-TE MUST be advertised using application > specific advertisements which have the L-flag clear. In cases where > some link attributes are shared with RSVP-TE, this requires duplicate > advertisements for those attributes. > > Maybe repeat that this duplication is required because the L flag > applies per-application per-link, for all attributes? > [Les:] Perhaps this is a matter of style. I prefer that a draft confine itself to normative statements whenever possible. You are suggesting that we should add some explanation – but as this aspect of L-bit is clearly defined earlier in the document I would prefer not to distract from the normative statement by adding an explanation which has already been provided. I am open to revision if you really think this is important – so let me know if you feel strongly about this. > Section 6.3.4 > > 2)Advertise all legacy link attributes using application specific > advertisements with L-flag clear and R-bit set. > > nit: I suggest clarifying that this involves duplicate advertisements > (legacy plus application-specific). Or at least, I assume it does, > since step (3) is "remove legacy advertisements". > [Les:] I have added “At this point both legacy and application specific advertisements are being sent.” > Section 7.3 > > Note to IANA: For future codepoints, in cases where the document > which defines the encoding is different from the document which > assigns the codepoint, the encoding reference MUST be to the document > which defines the encoding. > > Why not list both as the reference? [Les:] Current format in the registries is to have only one reference. Changing that is out of scope for this document. FWIW, I am fine with a single reference. > > Note to designated experts: If a link attribute can be advertised > both as a sub-TLV of TLVs 22, 23, 25, 141, 222, and 223 and as a sub- > sub-TLV of the Application Specific Link Attributes sub-TLV defined > in this document, then the same numerical code should be assigned to > the link attribute whenever possible. > > Are these notes intended to end up in the final RFC, attached to the > registry, both places, or neither place? [Les:] These notes will be part of the final RFC. The RFC number will also be listed in the “Reference” at the beginning of the registry. For example, currently we have: https://www.iana.org/assignments/isis-tlv-codepoints/isis-tlv-codepoints.xhtml#isis-tlv-codepoints-22-23-25-141-222-223 … Reference [RFC5305][RFC5316][RFC7370][RFC8668] > Section 7.4 > > policy for this registry is "Standards Action" [RFC8126]. Bit > definitions SHOULD be assigned in ascending bit order beginning with > Bit 0 so as to minimize the number of octets that will need to be > transmitted. The following assignments are made by this document: > > I worry a little bit that this will encourage codepoint squatting, > though in theory the user-defined bitmask should avoid the need for > squatting. > [Les:] Not sure why you are worried nor what you are suggesting should be changed. ?? > Section 7.5 > > Note to IANA: For future codepoints, in cases where the document > which defines the encoding is different from the document which > assigns the codepoint, the encoding reference MUST be to the document > which defines the encoding. > > (As above, why not list both?) [Les:] See my response above. Les > >
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