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:
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.
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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