Hi, Adrian: Thanks for your detail analysis and logical deduction! It help us to understand the arguments of each other. Let me give my thoughts to your analysis: First, I must point out that the base of your assumptions is NOT CORRECT: There is no such “Fixed part” that can be used as the “key” information for slicing the large TLV, defined in the related RFCs, for every possible MP-TLVs that are listed in draft-ihttps://datatracker.ietf.org/doc/html/draft-ietf-lsr-multi-tlv-09#section-9 We should all know there are fixed fields defined in these TLVs/sub-TLVs, but that can’t be solely used as the “Fixed part” to concatenate the several pieces together. We can take the TLV 22(Extended IS Reachability) as one example(also in this WGLC document). For clarity, I extracted the related content from the document directly(https://datatracker.ietf.org/doc/html/draft-ietf-lsr-multi-tlv-09#section-3.2.1): As an example, consider the Extended IS Reachability TLV (type 22). A neighbor in this TLV is specified by:¶ · 7 octets of system ID and pseudonode number¶ · 3 octets of default metric¶ · Optionally one or more of the following link identifiers:¶ o IPv4 interface address and IPv4 neighbor address as specified in [RFC5305]¶ o IPv6 interface address and IPv6 neighbor address as specified in [RFC6119]¶ o Link Local/Remote Identifiers as specified in [RFC5307]¶ The key consists of the 7 octets of system ID and pseudonode number plus the set of link identifiers which are present. We can check the original definition of RFC for TLV 22----RFC 5305----There is no any “key” definition information in this RFC----Verify what I have said above that there is no key definition for every possible MP-TLVs in current RFCs. What constitutes the key of TLV 22 is only mentioned in this WGLC document------“The key consists of the 7 octets of system ID and ……” Even we continuing our discussions based on such key definition information, can you tell me what is the “Fixed part” that you mentioned when slicing the TLV in your example? I think you should know, according to the description of this document, “the set of link identifiers” is optionally. I can image if the sender/receiver are from one vendor, they can keep the “Fixed part” in different pieces same, but, how to ensure they are same if the devices from different vendors? Comparing to this undefined and ambiguity of “Fixed part”, or “key” information for each possible MP-TLV, other issues that you raised(slicing not in the boundary of sub-TLV, temporarily duplicate of a TLV in two LSPs etc. can be easily mitigated). I think you admitted the “key” must be represented in every of piece of the sliced TLV/sub-TLVs(for the “keyed TLV” that you mentioned). Then, where is “key” definition for each of such TLV/sub-TLVs? Best Regards Aijun Wang China Telecom 发件人: forwardingalgorithm@xxxxxxxx [mailto:forwardingalgorithm@xxxxxxxx] 代表 Adrian Farrel The correct formation of a TLV includes certain fields that must be present and other fields (such as sub-TLVs) that may be present and may recur. All instances of a TLV must be formatted correctly. That means that when a TLV is repeated as part of an MP-TLV each component TLV must be correctly formatted. In other words, t is incorrect to read this document as simply saying that the “overflow” appears in a second TLV structure with the same Type, and with the data continuing. Consider (please enable non-proportional font) | T=t | L | Fixed part | sub-TLV1 | sub-TLV2 | sub-TLV3 | 1 ... ... 255 ... There is too much to fit into one TLV structure. The incorrect MP-TLV would be… | T=t | L | Fixed part | sub-TLV1 | | T=t | L | sub-TLV2 | sub-TLV3 | The correct MP-TLV would be | T=t | L | Fixed part | sub-TLV1 | | T=t | L | Fixed part | sub-TLV2 | sub-TLV3 | Note also, that the separation into component TLVs must happen at a segmentable boundary. E.g., at a sub-TLV. Thus, another incorrect MP-TLV would be… | T=t | L | Fixed part | sub-TLV1 | First part of sub-TLV2 | | T=t | L | Fixed part | Second part of sub-TLV2 | sub-TLV3 | There are two cases: - TLVs that have a key defined - TLVs that don’t have a key defined If the TLV has a key, that is usually found in the fixed part. Thus, the key is found in both component TLVs. What are the concerns?
ignore the TLV.
I say “yes”. Because, without a key you know that the TLV is “one of a kind”. Note: There are two cases identified in the document where (without MP-TLV) an un-keyed TLV may be duplicated. o sender makes an error by including multiple versions of a TLV o the sender is transiting a TLV from one LSP to another (so it appears in both LSPs) These are both handled by allowing concatenation to proceed, and the composed TLV to be discovered to be incorrectly formatted. My question back to you would be to ask you to give an example where this goes wrong? Thanks, Adrian From: Aijun Wang <wangaijun@xxxxxxxxxxxxxxx> Hi, Adrian: I have read your Rtgdir reviews and update suggestions on the current document. Appreciate for your efforts! But, I don’t know why you ignore the issues that you have concerned previously also about the “explicit key” definition of each possible IS-IS TLV/sub-TLV.(Please refer to: https://mailarchive.ietf.org/arch/msg/lsr/Xga5YrD6ObbNDvFFK_nVDXlipJA/). Let’s try to don’t loop the past arguments and make the life better. Then, would you, and also other experts/reviewer that pass this document answer the following simple, straightforward question: Can you concatenate several pieces together without one “explicit key” to identify them belong to the same segment? If the answer is “can”, please tell me how? If the answer is “can’t”, then, where is necessary “explicit key” in this document? And, if there is none of such “explicit key” information, what’s the value of this document? Let’s be clear for the further discussion, the implicit negotiations solution to solve the interoperability is not STANDARD solution. I copied this discussions also to the IESG mail list for further evaluations of the IESG experts. Best Regards Aijun Wang China Telecom 发件人: forwardingalgorithm@xxxxxxxx [mailto:forwardingalgorithm@xxxxxxxx] 代表 Adrian Farrel Many thanks for your responsiveness, Les. V9 addresses all of my nits adequately. I will update the status of my review in the Datatracker. As to… > That said, after posting V9, I thought maybe something like what I show below > might be added to Section 4. I am not convinced it is needed – but let me know > what you think. > > “Each TLV that is part of an MP-TLV MUST be parsable independent of other > TLVs in the MP-TLV. Breaking of a single sub-TLV or other data unit across TLVs > MUST NOT be done.” I agree with you that this is “not needed.” I do believe it would be somewhat helpful to avoid people falling into error. I leave it to you and your co-authors to decide. Cheers, Adrian |
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