Hi,
So I agree that using this new container TLV along with old TLVs doesn't help. However, it is worth nothing that if *only* the container TLV was used (i.e., once a TLV became too large it would be removed and placed inside container TLVs) then it would actually represent a safer way to deploy this "multiple tlv" functionality. If the container only was used, then only routers that understood would be able to use *any* of the TLV data. This would actually solve the problem of "newly inserted legacy router brings everything back down" that using a required capability bit being set on all routers has. This later issue with the capability bit is why no-one wanted to use a it, and why we currently have this very sub-optimal "solution" of "just do it and hope it works". Thanks, Chris. [as wg-member] P.S. the quoting style used in this thread is fabulously hard to comprehend in a text based email client.. What's wrong with good old ">>>" quoting style anyway? "Les Ginsberg (ginsberg)" <[email protected]> writes:
Huaimo – Please see inline. From: Huaimo Chen <[email protected]> Sent: Sunday, March 26, 2023 3:41 AM To: Les Ginsberg (ginsberg) <[email protected]>; [email protected]; [email protected] Subject: Re: Comments on draft-chen-lsr-isis-big-tlv-00 Hi Les, Thanks much for your comments. My responses are inline below with HC. Best Regards, Huaimo From: Les Ginsberg (ginsberg) <[email protected]> Sent: Thursday, March 23, 2023 3:35 AM To: [email protected] <[email protected]>; [email protected] < [email protected]> Subject: Comments on draft-chen-lsr-isis-big-tlv-00 Folks - This draft proposes a new way to handle advertisement of more than 255 bytes of information about a given object. It defines a new "container TLV" to carry additional information about an object beyond the (up to) 255 bytes of information advertised in an existing TLV. The draft is defining a solution to a problem which has already been addressed without requiring any protocol extensions. [HC]: It seems that a protocol includes a set of procedures. Would you mind telling me which existing protocols can be used to resolve the problem without requiring any protocol extensions? [LES:] Please read draft-pkaneria-lsr-multi-tlv-02 carefully. Section 1 documents that there are existing RFCs which explicitly state that multiple TLVs for the same object are allowed to be sent. What the draft goes on to discuss is the use of the same mechanism (sending multiple TLVs for the same object) in cases where existing RFCs have not explicitly stated this behavior. It is also a fact that there are multiple implementations from multiple vendors already shipping that utilize this mechanism for TLVs such as Neighbor and Prefix reachability. The existing solution - discussed in https://datatracker.ietf.org/doc /draft-pkaneria-lsr-multi-tlv/ has already been successfully implemented and deployed by multiple vendors. [HC]: You are a co-author of this draft, called a first draft for resolving the problem on big TLVs. This first draft contains some protocol extensions. If there is a solution for the problem without requiring any protocol extensions, then why do you as a co-author work on the first draft with protocol extensions? [LES:] There are no protocol extensions defined in draft-pkaneria-lsr-multi-tlv-02 (please see the statement in the IANA section). The draft has been written to clarify existing behavior and to discuss best deployment practices in cases where not all implementations support reception of multiple TLVs for a given object. The definition of a second solution to the problem is not needed - and in fact further complicates both implementation and deployment. Should the existing solution be used? Should the new solution be used? What is the state of support by all nodes in the network for each solution? [HC]: It seems better to merge the two drafts (i.e., the first draft and the second draft defining container TLV) into one. [LES:] This would the worst possible outcome. It would define two mechanisms for sending more than 255 bytes of information about an object. This would require implementations to support two different mechanisms for advertising the same information – also requiring the ability to control which mechanism should be used in a given deployment and even raising the possibility that both forms would need to be sent in parallel. This adds unnecessary complexity to implementations. For operators deploying features+scale which require such support, they would now have to identify not only whether all implementations in their deployment support sending/receiving more than 255 bytes/ object, but also which form of advertisement is supported – further complicating deployment considerations. And since there are explicit statements requiring the current form of advertisement to be used for some TLVs, behavior would potentially differ on a per TLV basis. The motivation for the new solution seems to be the notion that it supports partial deployment. Text in https://www.ietf.org/archive/id/ draft-chen-lsr-isis-big-tlv-00.html#name-incremental-deployment states: "For a network using IS-IS, users can deploy the extension for big TLV in a part of the network step by step. The network has some nodes supporting the extension (or say new nodes for short) and the other nodes not supporting the extension (or say old nodes for short) before the extension is deployed in the entire network." This suggests the authors believe that a network can function with some nodes using all of the advertisements and some nodes using only the legacy advertisements, but this is obviously false. Fundamental to operation of a link state protocol is that all nodes in the network operate on identical LSPDBs. The suggestion that features will work correctly when some nodes use attributes advertised in legacy TLVs and the new container TLV while some nodes use only the attributes advertised in legacy TLVs is simply incorrect. [HC]: Every node in the network has the same LSPDB. The new nodes understand the new container TLVs and may use them. The old nodes do not understand them and do not use them. [LES:] Consider the following simple example. Node A needs to send 10 sub-TLVs about a particular object – requiring more than 255 bytes to be sent. Some nodes in the network do not support reception of more than 255 bytes/object. Consider two such nodes. Node B, based on the local configuration, needs to be able to receive sub-TLVs 1,3,5,7,9 from A. Node C, based on local configuration, needs to be able to receive sub-TLVs 2,4,6,8,10 from A. There is no way that A can advertise all 10 sub-TLVs in a way which allows both B and C to correctly process the sub-TLVs they require. Network functionality is compromised. It is true that even with the existing solution unless all nodes are capable of processing more than 255 bytes of information/object network functionality will be compromised. That is exactly what motivated the writing of draft-pkaneria-lsr-multi-tlv. But your proposal does nothing to make that requirement easier to address. It in fact makes implementation/deployment even more difficult – as I have described above. It is also important to also state that the advertisement of more than 255 bytes of information is driven by configuration – not a protocol implementation choice. Suppressing advertisement of some of the configured information also does not result in a working network. In short, there is no positive value from the proposed extension – and it does harm by further complicating implementations and deployments. [HC]: The second draft defines a general mechanism for resolving the problem. It is backward compatible and simple. It does not do any harm. [LES:] You are proposing a second solution for a problem that has already been solved. In doing so you are introducing new problems and not solving any existing issues. Saying this “does no harm” is clearly false. Les The draft should be abandoned. Les _______________________________________________ Lsr mailing list [email protected] https://www.ietf.org/mailman/listinfo/lsr
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