Huaimo - You don't provide an operational definition of how to determine whether "all nodes need to have the same new information", but it is easy to come up with cases where this is needed. Parag described one below and I have previously described one related to Flex Algo.
I have yet to see you (or anyone else) present an example where "only the new nodes" need to use the additional information. But even if such examples exist, the logic required to determine this would be expensive and difficult to define in a robust way. And the state could change dynamically as sub-TLVs are added/removed. Deploying something that at best works some of the time is certain to lead to big problems. Our responsibility is to define robust solutions. Les From: Parag Kaneriya <pkane...@juniper.net> Sent: Friday, December 8, 2023 8:29 AM To: Huaimo Chen <huaimo.c...@futurewei.com>; Les Ginsberg (ginsberg) <ginsb...@cisco.com>; li_zhenqi...@hotmail.com; Tony Li <tony...@tony.li>; Linda Dunbar <linda.dun...@futurewei.com> Cc: Yingzhen Qu <yingzhen.i...@gmail.com>; draft-pkaneria-lsr-multi-...@ietf.org; lsr <lsr@ietf.org> Subject: RE: Re: [Lsr] WG Adoption Call - draft-pkaneria-lsr-multi-tlv (11/17/2023 - 12/09/2023) Legacy node gets half information result in the inconsistent view of network (for example TED [traffic engineering database] inconsistency lead to many network related issue.) hence legacy node getting half information is not backward consistent. Juniper Business Use Only From: Huaimo Chen <huaimo.c...@futurewei.com<mailto:huaimo.c...@futurewei.com>> Sent: Friday, December 8, 2023 7:23 PM To: Les Ginsberg (ginsberg) <ginsb...@cisco.com<mailto:ginsb...@cisco.com>>; li_zhenqi...@hotmail.com<mailto:li_zhenqi...@hotmail.com>; Tony Li <tony...@tony.li<mailto:tony...@tony.li>>; Linda Dunbar <linda.dun...@futurewei.com<mailto:linda.dun...@futurewei.com>> Cc: Yingzhen Qu <yingzhen.i...@gmail.com<mailto:yingzhen.i...@gmail.com>>; draft-pkaneria-lsr-multi-...@ietf.org<mailto:draft-pkaneria-lsr-multi-...@ietf.org>; lsr <lsr@ietf.org<mailto:lsr@ietf.org>> Subject: RE: Re: [Lsr] WG Adoption Call - draft-pkaneria-lsr-multi-tlv (11/17/2023 - 12/09/2023) [External Email. Be cautious of content] Hi Les, Your definition of backwards compatibility means that protocol extensions can be advertised and safely used in the presence of legacy nodes (which do not understand the new advertisements). Protocol extensions for Big-TLV include a new TLV (called container TLV) and a new Sub-TLV (called Big-TLV Capability Sub-TLV). Big-TLV is also short for Protocol extensions for Big-TLV. When adding a piece of new information into an existing TLV makes the TLV > 255, this new information can be put into a container TLV. The container TLV can be advertised in a network. The old/legacy nodes (i.e., the nodes not supporting Big-TLV) ignore the container TLV, which contains the new information. The new nodes (i.e., the nodes supporting Big-TLV) obtain the new information. Each of the new nodes advertises a Big-TLV Capability Sub-TLV, indicating the capability of Big-TLV. The old/legacy nodes ignore it. The new nodes get it. If it is not required that all the nodes must have the same new information for using the new information, the new nodes can use the new information, the old/legacy nodes ignore the new information. If all the nodes need to have the same new information for using the new information, every node needs to check if all the nodes support the Big-TLV. If all the nodes support it, every node uses the new information. >From the above, we can see that "the protocol extensions (: container TLV and >Big-TLV capability Sub-TLV, which is protocol extensions for Big-TLV) can be >advertised and safely used in the presence of legacy nodes (which do not >understand the new advertisements)". The quoted is your definition of >backwards compatibility. So, the Big-TLV is backwards compatible. Best Regards, Huaimo From: Les Ginsberg (ginsberg) <ginsb...@cisco.com<mailto:ginsb...@cisco.com>> Sent: Thursday, December 7, 2023 1:07 PM To: Huaimo Chen <huaimo.c...@futurewei.com<mailto:huaimo.c...@futurewei.com>>; li_zhenqi...@hotmail.com<mailto:li_zhenqi...@hotmail.com>; Tony Li <tony...@tony.li<mailto:tony...@tony.li>>; Linda Dunbar <linda.dun...@futurewei.com<mailto:linda.dun...@futurewei.com>> Cc: Yingzhen Qu <yingzhen.i...@gmail.com<mailto:yingzhen.i...@gmail.com>>; draft-pkaneria-lsr-multi-...@ietf.org<mailto:draft-pkaneria-lsr-multi-...@ietf.org>; lsr <lsr@ietf.org<mailto:lsr@ietf.org>> Subject: RE: Re: [Lsr] WG Adoption Call - draft-pkaneria-lsr-multi-tlv (11/17/2023 - 12/09/2023) Huaimo - There are some things on which people can legitimately have different opinions - the meaning of backwards compatibility is not one of them. Your position seems to be that so long as I introduce a capability advertisement that controls whether a new advertisement is used when received that I can declare it "backwards compatible". By that definition everything is "backwards compatible". This makes the term "backwards compatibility" meaningless. This POV is neither useful nor sensible. Les From: Huaimo Chen <huaimo.c...@futurewei.com<mailto:huaimo.c...@futurewei.com>> Sent: Thursday, December 7, 2023 6:07 AM To: Les Ginsberg (ginsberg) <ginsb...@cisco.com<mailto:ginsb...@cisco.com>>; li_zhenqi...@hotmail.com<mailto:li_zhenqi...@hotmail.com>; Tony Li <tony...@tony.li<mailto:tony...@tony.li>>; Linda Dunbar <linda.dun...@futurewei.com<mailto:linda.dun...@futurewei.com>> Cc: Yingzhen Qu <yingzhen.i...@gmail.com<mailto:yingzhen.i...@gmail.com>>; draft-pkaneria-lsr-multi-...@ietf.org<mailto:draft-pkaneria-lsr-multi-...@ietf.org>; lsr <lsr@ietf.org<mailto:lsr@ietf.org>> Subject: RE: Re: [Lsr] WG Adoption Call - draft-pkaneria-lsr-multi-tlv (11/17/2023 - 12/09/2023) Hi Les, My responses are inline below with [HC]. Best Regards, Huaimo Folks - The term "backwards compatibility" is getting abused here. What does "backwards compatibility" mean in the context of a routing protocol like IS-IS? It means that protocol extensions can be advertised and safely used in the presence of legacy nodes (which do not understand the new advertisements). Neither MP nor Big-TLV are backwards compatible. [HC]: Big-TLV is backwards compatible according to your definition of "backwards compatibility". The authors of MP draft do not claim it is backwards compatible. The authors of Big-TLV claim it is "backwards compatible" - but this is a false statement. Any attempt to use Big-TLV advertisements in the presence of legacy nodes will result in inconsistent and potentially dangerous behavior. [HC]: Using Big-TLV advertisements in the presence of legacy nodes will not result in any inconsistent or potentially dangerous behavior. I have explained this in detail in the LSR mailing list. Big-TLV authors like to say "you can send Big-TLV but not use it until all nodes support it" - but this does meet the criteria for backwards compatibility. If Big-TLV were "backwards compatible" there would be no need for a capability advertisement to determine when it is safe to use the advertisements. [HC]: Big-TLV capability advertisement is a part of the Big-TLV solution/extension. Capability advertisements seem used for backwards compatibility by other protocols. Is there any restriction in IS-IS that does not allow any IS-IS extension to use a capability advertisement for backwards compatibility? Using a capability for Big-TLV backwards compatibility is suggested by Chris in the LSR mailing list. https://mailarchive.ietf.org/arch/msg/lsr/cXyGnSJSdEQR9BVxykXhiuUWtgE/<https://urldefense.com/v3/__https:/mailarchive.ietf.org/arch/msg/lsr/cXyGnSJSdEQR9BVxykXhiuUWtgE/__;!!NEt6yMaO-gk!AJLJQdgI6o8QZjFz5qqOIwctEmPuG3EFbGiRTES1QSMvsb66UrDE-5gYwrwO6Lkixe1VZHoK_qNbccOeOBnLp4XY$> Les From: Les Ginsberg (ginsberg) <ginsb...@cisco.com<mailto:ginsb...@cisco.com>> Sent: Tuesday, December 5, 2023 2:11 AM To: li_zhenqi...@hotmail.com<mailto:li_zhenqi...@hotmail.com>; Huaimo Chen <huaimo.c...@futurewei.com<mailto:huaimo.c...@futurewei.com>>; Tony Li <tony...@tony.li<mailto:tony...@tony.li>>; Linda Dunbar <linda.dun...@futurewei.com<mailto:linda.dun...@futurewei.com>> Cc: Yingzhen Qu <yingzhen.i...@gmail.com<mailto:yingzhen.i...@gmail.com>>; draft-pkaneria-lsr-multi-...@ietf.org<mailto:draft-pkaneria-lsr-multi-...@ietf.org>; lsr <lsr@ietf.org<mailto:lsr@ietf.org>> Subject: RE: Re: [Lsr] WG Adoption Call - draft-pkaneria-lsr-multi-tlv (11/17/2023 - 12/09/2023) Folks - The term "backwards compatibility" is getting abused here. What does "backwards compatibility" mean in the context of a routing protocol like IS-IS? It means that protocol extensions can be advertised and safely used in the presence of legacy nodes (which do not understand the new advertisements). Neither MP nor Big-TLV are backwards compatible. The authors of MP draft do not claim it is backwards compatible. The authors of Big-TLV claim it is "backwards compatible" - but this is a false statement. Any attempt to use Big-TLV advertisements in the presence of legacy nodes will result in inconsistent and potentially dangerous behavior. Big-TLV authors like to say "you can send Big-TLV but not use it until all nodes support it" - but this does meet the criteria for backwards compatibility. If Big-TLV were "backwards compatible" there would be no need for a capability advertisement to determine when it is safe to use the advertisements. Les From: li_zhenqi...@hotmail.com<mailto:li_zhenqi...@hotmail.com> <li_zhenqi...@hotmail.com<mailto:li_zhenqi...@hotmail.com>> Sent: Monday, December 4, 2023 10:35 PM To: Huaimo Chen <huaimo.c...@futurewei.com<mailto:huaimo.c...@futurewei.com>>; Les Ginsberg (ginsberg) <ginsb...@cisco.com<mailto:ginsb...@cisco.com>>; Tony Li <tony...@tony.li<mailto:tony...@tony.li>>; Linda Dunbar <linda.dun...@futurewei.com<mailto:linda.dun...@futurewei.com>> Cc: Yingzhen Qu <yingzhen.i...@gmail.com<mailto:yingzhen.i...@gmail.com>>; draft-pkaneria-lsr-multi-...@ietf.org<mailto:draft-pkaneria-lsr-multi-...@ietf.org>; lsr <lsr@ietf.org<mailto:lsr@ietf.org>> Subject: Re: Re: [Lsr] WG Adoption Call - draft-pkaneria-lsr-multi-tlv (11/17/2023 - 12/09/2023) Hello All, It seems Big-TLV is backward compatible. Backward compatible is an important point that should be considered when we introduce new features in a protocol, especially the widely used protocols like ISIS, BGP etc. ________________________________ Best Regards, Zhenqiang Li China Mobile li_zhenqi...@hotmail.com<mailto:li_zhenqi...@hotmail.com> From: Huaimo Chen<mailto:huaimo.c...@futurewei.com> Date: 2023-12-04 21:57 To: Les Ginsberg (ginsberg)<mailto:ginsberg=40cisco....@dmarc.ietf.org>; Tony Li<mailto:tony...@tony.li>; Linda Dunbar<mailto:linda.dun...@futurewei.com> CC: Yingzhen Qu<mailto:yingzhen.i...@gmail.com>; draft-pkaneria-lsr-multi-...@ietf.org<mailto:draft-pkaneria-lsr-multi-...@ietf.org>; lsr<mailto:lsr@ietf.org> Subject: Re: [Lsr] WG Adoption Call - draft-pkaneria-lsr-multi-tlv (11/17/2023 - 12/09/2023) Hi Les, My responses are inline below with [HC]. Best Regards, Huaimo Linda - When we have polarized positions (for whatever reasons), coming to consensus is often difficult. Each side tends to dismiss the arguments of the other - sometimes regardless of merit. So, maybe the following won't help - but I am going to give it a try. Point #1: There are existing TLVs for which MP behavior was explicitly stated in existing RFCs and there are already many deployments that conform to those RFCs (see Introduction of MP draft for a list). If we choose to use a different encoding to support > 255 bytes for other codepoints, this both complicates implementations and confuses the definition of new protocol extensions. When defining a new codepoint should I choose MP or should I choose a different encoding? And what criteria can be used to make this choice a sensible one? And since MP is already REQUIRED for those TLVs where it was explicitly defined, we will always have to support that - at least for some codepoints. [HC]: When Big-TLV is used for a TLV > 255, it does not affect the existing MP-TLV that has been used for another TLV > 255. When defining a new codepoint for a new TLV, it seems better to choose Big-TLV if backward compatibility is needed for the new TLV since Big-TLV is backward compatible. I have explained it (i.e. ,"Big-TLV is backward compatible") in detail. In addition, some other people indicate it in the LSR mailing list. Point #2: MP for IS-Neighbor/Prefix Reachability TLVs has already been implemented by multiple vendors, tested in both partial deployment and full deployment scenarios. We know that it works and we know what the problems are in partial deployment. This cannot be said for new alternatives. With due respect to Huaimo, he tends to characterize the implementation problems to be solved for Big-TLV as "easy to resolve" but given the absence of implementation I think this is an overly optimistic and somewhat naïve POV. (No offense intended) [HC]: It seems that the implementation of an idea/solution in a draft is not required by LSR WG for the draft to be adopted, or even for the draft to become RFC. Point #3: As documented in the IANA section of the MP draft, the problem extends to sub-TLVs of top level TLVs as well. It is then not as simple as reserving one encap TLV to handle the top-level TLV case. We also have to have a solution when a sub-TLV requires more than 255 bytes. MP solves this without additional changes. Big-TLV has yet to discuss this. [HC]: It seems that MP-TLV has to discuss this. Assume: a TLV (e.g., TLV 1) > 255 and its sub-TLV > 255, there are MP-TLVs (e.g., MP-TLV 1 and MP-TLV 2) for the TLV and MP-TLVs (e.g., MP-TLV 3 and MP-TLV 4) for the sub-TLV. All these MP-TLVs are TLVs. If there is another TLV (e.g., TLV 2) > 255 and its sub-TLV > 255 and all these sub-TLVs (i.e., the sub-TLV of TLV 1 and the sub-TLV of TLV 2) have the same type and there are MP-TLVs (e.g., MP-TLV 5, MP-TLV 6) for TLV 2 and MP-TLVs (e.g., MP-TLV 7, MP-TLV 8) for the sub-TLV (of TLV 2) > 255, how do you handle this case? How do you map MP-TLVs (e.g., MP-TLV 3, 4, 7, 8) for the same type of the sub-TLVs to their TLVs (e.g., TLV 1, 2)? If Big-TLV actually solved the partial deployment case, we would have a motivation to look at it more seriously. But it does not. It has the same issue with partial deployment that MP does. So for me, there is no value add to Big-TLV - and it does require additional implementation work - not all of which has even been defined yet. [HC]: Big-TLV actually solved the partial deployment case. I have explained this in detail. In addition, some other people indicate that Big-TLV is backward compatible in the LSR mailing list. It isn't better - it is just different - and comes with additional implementation costs. [HC]: Big-TLV is better as I have explained in detail. Les From: Tony Li <tony1ath...@gmail.com<mailto:tony1ath...@gmail.com>> On Behalf Of Tony Li Sent: Friday, December 1, 2023 2:44 PM To: Linda Dunbar <linda.dun...@futurewei.com<mailto:linda.dun...@futurewei.com>> Cc: Yingzhen Qu <yingzhen.i...@gmail.com<mailto:yingzhen.i...@gmail.com>>; draft-pkaneria-lsr-multi-...@ietf.org<mailto:draft-pkaneria-lsr-multi-...@ietf.org>; lsr <lsr@ietf.org<mailto:lsr@ietf.org>> Subject: Re: [Lsr] WG Adoption Call - draft-pkaneria-lsr-multi-tlv (11/17/2023 - 12/09/2023) Hi Linda, * Suppose the information to be carried by the Extended IS Reachability (type 22) (in Example 4.1) is larger than 255. Does it mean the recipient will receive 2 TLVs (both with the Type 22) in one LSA? For legacy routers, the second TLV (Type =22) might overwrite the first TLV. Yes, a legacy implementation may well have bugs. The proposal is to fix that: expect MP-TLVs. [Linda] Are you saying only the legacy implementation with bugs will be confused with two TLVs with the same Type in in one LSA? No. All implementations have bugs. This is reality. Implementations that do not understand MP-TLV may be confused. Correct implementations of MP-TLV support will not be confused. * Isn't it more straightforward to have a new TYPE value for carrying the extra information beyond the 255 bytes? So, the legacy routers can ignore the TLVs with the unrecognized types. You could do that, but code points are not free. We certainly cannot afford another code point for each existing code point. Using just one code point is less than helpful: it forces us to aggregate information that has no business being aggregated. Ignoring information is a non-starter because it makes partial deployments fatal: some of the domain operates with some information and some of the domain operates with different information. [Linda] Why not consider having just one additional TYPE code with sub-types to indicate which original TLVs the value should be appended to? We have considered it. See all of Les' emails for why it's a bad idea. If it helps simplify this debate: we know that you work for Futurewei/Huawei and that the discussion has polarized into your Big-TLV faction vs. everyone else. Repetition of previously made points add zero value to the discussion. Tony
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