Re: [Idr] Alia's AD review of draft-ietf-idr-ls-distribution-10
"Susan Hares" <shares@ndzh.com> Wed, 30 September 2015 17:42 UTC
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From: Susan Hares <shares@ndzh.com>
To: 'Alia Atlas' <akatlas@gmail.com>, 'Adrian Farrel' <adrian@olddog.co.uk>
References: <03e701d0faff$b9e484b0$2dad8e10$@olddog.co.uk> <CAG4d1rfoqnfq89rByefqXfCVBc1Sx6iW0Fx-87F4me-q291OCw@mail.gmail.com>
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Date: Wed, 30 Sep 2015 13:42:17 -0400
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Cc: "'idr@ietf. org'" <idr@ietf.org>, draft-ietf-idr-ls-distribution@ietf.org, 'Alia Atlas' <akatlas@juniper.net>
Subject: Re: [Idr] Alia's AD review of draft-ietf-idr-ls-distribution-10
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Adrian: One procedural and one technical question. Did you intend a date of June 4, 2015? If so, why? Technical: Do you believe that sections 6.1.1 and sections 6.1.5 are sufficient to describe what happens if the extra NLRI do not get sent the private infrastructure of route-reflectors Sections include below from -11. Sue Hares WG chair hat on <https://tools.ietf.org/html/draft-ietf-idr-ls-distribution-11#section-6.1.1> 6.1.1. Operations Existing BGP operational procedures apply. No new operation procedures are defined in this document. It is noted that the NLRI information present in this document purely carries application level data that has no immediate corresponding forwarding state impact. As such, any churn in reachability information has different impact than regular BGP updates which need to change forwarding state for an entire router. Furthermore it is anticipated that distribution of this NLRI will be handled by dedicated route-reflectors providing a level of isolation and fault-containment between different NLRI types. <https://tools.ietf.org/html/draft-ietf-idr-ls-distribution-11#section-6.1.5> 6.1.5. Impact on Network Operation Frequency of Link-State NLRI updates could interfere with regular BGP prefix distribution. A network operator MAY use a dedicated Route- Reflector infrastructure to distribute Link-State NLRIs. Distribution of Link-State NLRIs SHOULD be limited to a single admin domain, which can consist of multiple areas within an AS or multiple ASes. From: Idr [mailto:idr-bounces@ietf.org] On Behalf Of Alia Atlas Sent: Tuesday, September 29, 2015 6:20 PM To: Adrian Farrel Cc: draft-ietf-idr-ls-distribution@ietf.org; Alia Atlas; idr@ietf. org Subject: Re: [Idr] Alia's AD review of draft-ietf-idr-ls-distribution-10 Hi Adrian, First, thank you for taking this up. The suggested resolutions are fine. I fully agree that many of these are minor comments or nits for better clarity - which is why I did the IETF Last Call in parallel with the expected response. As for describing the idea that there is no management information needed as "clearly absurd and ludicrous", I am sorry if that sounded over the top. This is a newer large use of BGP. The idea that no new management information would be needed as BGP-LS takes off does seem quite unlikely to me, but perhaps we'll merrily get along. "Does not mandate" still sounds like a someone-else's-problem field. Your text at least has the benefit of explaining why the authors think nothing is needed. Regards, Alia On Tue, Sep 29, 2015 at 5:42 PM, Adrian Farrel <adrian@olddog.co.uk> wrote: Hi, Alvaro noted that there didn't appear to be a follow-up to Alia's review from March 2015 in the archive even though -11 was produced. Here is one co-author's response: > As is customary upon receiving a publication request, I have done my AD review of > draft-ietf-idr-ls-distribution. First, thanks for the hard work on this very useful and > non-trivial specification. Second, I have found a number of clarifications and issues > that I would like to see resolved in the draft. > > I will start an IETF Last Call so that you can get additional comments in parallel. Because > of the upcoming IETF, I expect this to run longer - ending April 8. > > 1) In Sec 3.2, 3rd paragraph last sentence, it says: > > "This is done as specified in [RFC4760], by using capability code 1 (multi-protocol > BGP), with an AFI 16388 / SAFI 71 and AFI 16388 / SAFI TBD for the VPN flavor." > Could you please turn this into non-colloquial language with clear requirements > language? Can one support "the VPN flavor" but not the regular? I am confused by the request and no change was made. 1. Is the concern with the word "flavor"? Perhaps it could read This is done as specified in [RFC4760], by using capability code 1 (multi-protocol BGP), with an AFI 16388 / SAFI 71 for BGP-LS, and AFI 16388 / SAFI TBD for BGP-LS-VPN." 2. How is 2119 language appropriate here? The previous sentence includes the normative language. The reference to 4760 is all you need to explain how you do the thing you MUST do. I propose no change. 3. Yes, one can follow the processes of 4760 and support any or all of the allowed SAFIs. > 2) On p. 9, the Route Distinguisher is introduced and its length is included - but no > reference is given nor length specified. Could you please provide both? I think the length forms part of the definition and would not want to redefine it here. I propose including... "Route Distinguishers are defined and discussed in [RFC4364]." ...adding a normative reference. > 3) In Sec 3.2.1, second paragraph, it says "We use Autonomous System (AS) Number and > BGP-LS Identifier (Paragraph 2) in order to disambiguate the Router-IDs, as described in > Section 3.2.1.1." > > I suspect that "Paragraph 2" is intended to refer to the last paragraph on p. 11 > - but that isn't a clear way to reference it; also the Identifier is not referred to > as a "BGP-LS Identifier" but merely an Identifier. Also, instead of "we" perhaps > "BGP-LS". How about... BGP-LS uses the Autonomous System (AS) Number and BGP-LS Identifier (see Section 3.2.1.4) to disambiguate the Router-IDs, as described in Section 3.2.1.1. > 4) In Sec 3.2.2, I see that link descriptors are actually only a unidirectional representation. > Could you please mention this when the link NLRI is introduced? I don't think that would be appropriate: the NLRI can be for node, link, or prefix, so it is only when the description narrows to the link state NLRI that we should mention the "half link" nature, and that is precisely section 3.2.2. > 5) In the NLRI format, I see a 64 bit identifier. From the discussion > (last paragraph in p. 11), it looks like this 64-bit identifier is intended > to be the 5-bit "Routing Universe Identifier" which is supposed > to indicate the protocol plus routing instance??? Where does the "5-bit" suggestion come from? 6549 has an 8 bit field for identifying instances. 6822 has a 16 bit IID. The overlap between the reserved values for this has been a constant joy. Anyway, turns out we need to allow for more than 16 bits to handle the full space. But I think you are assuming that there is a protocol mapping from the IGP IID to the BGP-LS IID. There is no such mapping required (although an implementation may choose to make one). The text is, IMHO, clear... The 64-Bit 'Identifier' field is used to identify the "routing universe" where the NLRI belongs. The NLRIs representing Link-state objects (nodes, links or prefixes) from the same routing universe MUST have the same 'Identifier' value. NLRIs with different 'Identifier' values MUST be considered to be from different routing universes. There is potentially a challenge with this open definition: suppose there are two BGP speakers both reporting routing information: a. Suppose they are both reporting on the same routing universe (for redundancy, I guess), how do they ensure that they use the same Identifier? b. Suppose they are reporting on different routing universes, how do they ensure they use different Identifiers? Answer: The BGP-LS Identifier (and ASN) ensure that we know that the BGP-LS speakers are coordinated. Beyond that, the coordination of Identifiers is not problem. > 5) In Sec 3.2.1.4: I see the OSPF Area-ID listed. How are IS-IS levels handled? I see the Node > Attribute TLV (1027) but this seems to require that a link would have to have its remote and > local nodes looked up to find the associated IS-IS Area Identifier. What would be actually > really useful is to describe, in the introduction, the different handling for IS-IS and OSPF in > the encapsulations and why they differ. I think you are referencing the entry in the table for 514. The text that follows... Area ID: It is used to identify the 32 Bit area to which the NLRI belongs. Area Identifier allows the different NLRIs of the same router to be discriminated. ...does not say "OSPF Area-ID" and should. The IS-IS Area ID is found in 3.3.1.2. > 6) In Sec 3.2.2 3rd from last paragraph: Can both IPv4 AND IPv6 addresses both > be included in the link descriptor? Presumably the same logic that prevents the > link local/remote identifiers from being included would apply? Also, why are the > neighbor addresses included for the Link Descriptor when the remote node's > descriptor should already be in the Remote Node Descriptor? It seems that there would be no reason to prohibit v4 and v6 addresses both being present if the IGP allows the local node of a link to advertise them both in the same advertisement. Your last question is, I think, answered with "because that's the way we did it." > 7) In Sec 3.2.3.1: It says "The OSPF Route Type field values are defined in the > OSPF protocol, and can be one of the following". Could you please add a > reference to which version of OSPF and what field you are describing? I > suspect it is the LSA types and they are different values between OSPFv2 > and OSPFv3. This section could benefit from some clarity. The LSA types help you to determine the route type and so build the routes in your routing table. It is true that the LSA types have different code points in the two versions of OSPF. But the set of route types is as described in 3.2.3.1 where they are listed and given code points for inclusion in the BGP-LS OSPF Route Type TLV. > 8) In Sec 3.3.1.2: Please add a reference and describe what an "Area Identifier > (variable)" is. I guess we would say: Area Identifier: The IS-IS Area Identifier. We could add in a reference to ISO 8348. And we could say its length is from 1 to 13 octets, but that is redefining the ISO spec. > 9) Sec 3.3.1.5: I like the idea of this - but an example or two in terms of encoding/ > parsing would be useful. You have a couple pointers - but it could use another > level of explanation. I don't see how such examples are realistic. As the text says, the primary purpose is to allow a way of passing a new piece of information in BGP-LS in the "lag" between it being added to the IGP and a BGP-LS extension being developed. The text does, however, cite two examples. Maybe the clue is in "transparently carries optional node attribute TLVs advertised by a router." To me that is clear, but maybe you are asking for additional text on this point. I'm not sure I can think of anything to say other than "cut the whole of all of the unknown TLVs including the T and the L fields from the IGP advertisement, and plop them into this TLV." I don't think adding that has value. > 10) Sec 3.3.2.2: I am not clear what the rationale for deciding what protocols to include > here is. For instance, is mLDP considered a different protocol or a subset of LDP? I > would like to see a short paragraph discussing how this information might be used > or what criteria would be applied to decide if another protocol should be added. > 8 bits is a pretty small space... Hmmm, how many "MPLS signaling protocols" have been defined in and survived through the last 15 years? I think this document lists both of them and that 2 out of 255 in 15 years is pretty safe. > 11) Sec 3.3.2.3: " If a source protocol (e.g. IS-IS) does not support a Metric width > of 32 bits then the high order octet MUST be set to zero." Surely you mean that > if the source protocol supports a metric width shorter than 32 bits, then the > metric is placed in the bottom of the word and the high order bits from the > supported metric width to 32 MUST be set to 0. As written, it assumes that > any source protocol that doesn't support 32 bits of metric must support exactly > 24 bits. Yes, it is fuzzy as a result of the known behaviors of IS-S and OSPF. But it would read better as... The TE Default Metric TLV carries the Traffic engineering metric for this link. The length of this TLV is fixed at 4 octets. If a source protocol uses a Metric width of less than 32 bits then the high order bits of this field MUST be padded with zero. > 12) Sec 3.3.2.5: Please correct the sentence that claims "Note that there is no > SRLG TLV in OSPF-TE". A simple browsing in the IANA registry > (http://www.iana.org/assignments/ospf-traffic-eng-tlvs/ospf-traffic-eng-tlvs.xht <http://www.iana.org/assignments/ospf-traffic-eng-tlvs/ospf-traffic-eng-tlvs.xhtml#subtlv2> ml#subtlv2 ) > clearly shows it defined: > > 16 Shared Risk Link Group (variable) [RFC4203] This was fixed in -11. > 13) Sec 3.3.3.1: How large are the bit fields that are mashed together from IS-IS > and OSPF to form the IGP Flags TLV? Can you please add some guidance on when > new flags should be allocated? There are currently four bits defined (1 for IS-IS and 3 for OSPF). It doesn't matter how large the source bit fields are as this TLV can extend to 65535 octets which seems like enough bits for the next couple of years. Since the "mashing" is via a definition of a new bit in a new BGP-LS spec (and not automagic) there doesn't seem to be a need for worry about the size. As to "when should a new flag be allocated?" The answer is "when a new IGP prefix flag is defined." That should be obvious from the definition of the field. > 14) Sec 3.3.3.2 and Sec 3.3.3.3: Please add a reference for OSPF TAGs. draft-acee-ospf- > admin-tags-01 seems to be the corresponding one. I think that the reference can be > Informational. It's really too early for that, isn't it? You can't publish an RFC that says "what goes in this field might be something a bit like what is defined in this individual draft". In fact, the best we could do is say: A future document may describe how to carry OSPF route tags in this TLV." > 15) Sec 3.3.3.4: The reference to RFC5305 is, I presume to Section 4. That would be useful to > clarify since it isn't easy to find. Similarly, where does the information come from in OSPF? > Could you please add a reference? We can certainly say "section 4". Does the concept of a prefix metric exist in OSPF-TE? I am not aware of it. > 16) Sec 3.5: Can you please provide more guidance here around what Protocol-ID > to use for inter-AS links - particularly if they are not in the IGP? Are there any issues > around the Protocol-ID implying the format for data that an inter-AS link might have? If they *are* advertised by the IGP, then surely there is no question about what identifiers to use since the advertisement in the IGP will nail that. If they are injected into BGP-LS then we could add "using identifiers that will make the inter-AS links visible as part of the topologies that will use them." Seemed a bit obvious. > 17) Sec 5 IANA Considerations: There are several fields (i.e. MPLS protocols, IGP Flags, etc) > that are not included in the IANA Considerations. The authors and document shepherd > should go through and describe how each field that is not managed by IANA would have > additional values added - or whether that isn't expected and why. Why should we do this? The authors have carefully considered which fields they believe need ANA registries and which do not. It is completely clear and there is plenty of precedent for how fields that do not have registries are extended if the need arises. I am usually a fan of registries, but only when it looks like they will be needed: in the cases where the rate of arrival of new values is likely to be low why have a registry? And certainly, why document the reasoning for each case in the RFC? > 18) Sec 6.2.1: I assume that by "does not mandate", the authors mean "we're > not doing it now"? It's clearly absurd and ludicrous to think that BGP-LS wouldn't > need some type of extensions - whether that is topology-related YANG models > or something else. Please figure out what you want to say other than "someone > else's problem" and put it in here. I think the authors meant the usual English language meaning of "does not mandate." There is nothing in this document that requires the development of new MIB information or YANG models. Of course, that does not preclude their development. You saying that the authors (and the WG?) are "clearly absurd and ludicrous" may account for the pissy tone of my whole email. The only other way I can find to write this section is: "The IDR working group has documented and continues to document parts of the Management Information Base and YANG models for managing and monitoring BGP speakers and the sessions between them. It is currently believed that the BGP session running BGP-LS is not substantially different from any other BGP session and can be managed using the same data models." Cheers, Adrian _______________________________________________ Idr mailing list Idr@ietf.org https://www.ietf.org/mailman/listinfo/idr
- [Idr] Alia's AD review of draft-ietf-idr-ls-distr… Adrian Farrel
- Re: [Idr] Alia's AD review of draft-ietf-idr-ls-d… Alia Atlas
- Re: [Idr] Alia's AD review of draft-ietf-idr-ls-d… Susan Hares
- Re: [Idr] Alia's AD review of draft-ietf-idr-ls-d… Adrian Farrel
- Re: [Idr] Alia's AD review of draft-ietf-idr-ls-d… Robert Raszuk
- Re: [Idr] Alia's AD review of draft-ietf-idr-ls-d… Susan Hares