Hi Weiqiang, 

I’m also curious as to how you are using 20 different flex algorithms. Is this 
just a hypothetical scenario
to illustrate the mathematics or do you have an actual use case? 

> On Apr 12, 2023, at 09:31, Peter Psenak <[email protected]> wrote:
> 
> Changwang,
> 
> please see inline (##PP2):
> 
> 
> On 12/04/2023 15:13, linchangwang wrote:
>> Hi Peter
>>  Please see inline [changwang lin].
>>> We've met the same problem when applying Flex Algo in SRv6 network.
>> what problem exactly, can you please describe it?
>> [changwang lin]
>> Advertisement size of per Flex-Algo Adj-SID in the network
>> Related to F(# of node, # of FA, # of links)
>> For a node with 1,000 links and 20 Flex-Algo
>>    n x 20 x 1000
>>    MPLS-SR:If n = 10 bytes, it is 200K bytes
>>    SRv6:   If n = 24 bytes, it is 400K+ bytes
>> If 500 nodes:
>>    MPLS-SR:it is 200K*500   =  100000k bytes
>>    SRv6:   it is 400K+ * 500  = 200000k bytes
>> If interface mtu=1500, lsp length = 1497
>>  LSPs num:
>>    MPLS-SR:10000k bytes/1497 = 66800  lsps
>>    SRv6:   20000k bytes/1497 = 160320 lsps
>> The number of LSPs is too large, and IS-IS needs to periodically refresh 
>> LSPs,
>> resulting in a decrease in ISIS performance and unstable network operation.
> 
> ##PP2
> above is hardly a realistic estimation.
> 
> In a network with 1k nodes, not every node will have 1k links.
> 
> Advertising large number of LSPs is not caused by Adj-SIDs.
> With TE enabled the amount of data flooded per link is larger than 
> advertisement of the 20 Adj-SID. The problem you are highlighting is not 
> specific to Adj-SIDs, it's generic.
> 
> LSP refresh time can be set to 18 hours and any reasonable implementation 
> does not refresh all LSPs at the same time.
> 
>> So we need to optimize on the control surface to save LSP space.
> 
> ##PP2
> with all the respect, I don't agree. The problem as you described it does not 
> exist.
> 
>> Through the optimization notification mechanism mentioned in these two 
>> documents,
>> we have greatly saved LSP space for IS-IS and improved the performance of 
>> IS-IS flex algo in large-scale networking.
>> At the same time, through the VFA mechanism, in other non flex algo 
>> application scenarios,
>>  such as network slicing scenarios, the LSP space of IS-IS can also be saved
> 
> ##PP2
> it seems to me you are trying to fix the implementation problem with the 
> protocol changes, which is never a good idea.
> 
> thanks,
> Peter
> 
>> thanks,
>> Changwang lin
>> -----Original Message-----
>> From: Lsr [mailto:[email protected]] On Behalf Of Peter Psenak
>> Sent: Wednesday, April 12, 2023 7:10 PM
>> To: 程伟强; Louis Chan; Les Ginsberg (ginsbe; Acee Lindem
>> Cc: lsr; Krzysztof Szarkowicz
>> Subject: Re: [Lsr] IETF-116 LSR - IGP extensions for Advertising Offset 
>> forFlex-Algorithm
>> Weiqiang,
>> please see inline (##PP):
>> On 12/04/2023 12:05, 程伟强 wrote:
>>> Hi Louis and Les,
>>> 
>>> 
>>> My two cents from operator perspective.
>>> 
>>> 
>>> We've met the same problem when applying Flex Algo in SRv6 network.
>> what problem exactly, can you please describe it?
>> [changwang lin]
>> Advertisement size of per Flex-Algo Adj-SID in the network
>> Related to F(# of node, # of FA, # of links)
>> For a node with 1,000 links and 20 Flex-Algo
>>    n x 20 x 1000
>>    MPLS-SR:If n = 10 bytes, it is 200K bytes
>>    SRv6:   If n = 24 bytes, it is 400K+ bytes
>> If 500 nodes:
>>    MPLS-SR:it is 200K*500   =  100000k bytes
>>    SRv6:   it is 400K+ * 500  = 200000k bytes
>> If interface mtu=1500, lsp length = 1497
>>  LSP num:
>>    MPLS-SR:10000k bytes/1497 = 66800  lsps
>>    SRv6:   20000k bytes/1497 = 160320 lsps
>> The number of LSPs is too large, and IS-IS needs to periodically refresh 
>> LSPs,
>> resulting in a decrease in ISIS performance and unstable network operation.
>> So we need to optimize on the control surface to save LSP space.
>> Through the optimization notification mechanism mentioned in these two 
>> documents,
>> we have greatly saved LSP space for IS-IS and improved the performance of 
>> IS-IS flex algo in large-scale networking.
>> At the same time, through the VFA mechanism, in other non flex algo 
>> application scenarios,
>>  such as network slicing scenarios, the LSP space of IS-IS can also be saved
>>> 
>>> 
>>> As the number of slices and the scale of the network increases, the
>>> convergence issue which is caused by SIDs  advertising and flooding
>>> becomes more and more serious.
>>> 
>>> 
>>> Due to the problem, it is impossible to apply Flex-Algo in the large
>>> network, such as the network with more than 1000 routers.
>> flex-algo has been successfully deployed in a networks that have more
>> that 1k nodes.
>> Maybe you want deploy the flex-algo for something that it was not
>> designed for.
>>> 
>>> 
>>> I believe Louis'draft provides a good idea to resolve this problem.
>>> Similar solution for SRv6 SIDs is described in another draft.
>> Again, what problem exactly?
>>  From what I see the drafts tries to pack algo SIDs to save space in
>> LSP. I don't see how it helps to to deploy flex-algo in a large scale
>> network.
>> thanks,
>> Peter
>>> 
>>> 
>>> About the SIDs assignment, I think it is better to have a scheduled
>>> assignment than a random assignment as Les mentioned.
>>> 
>>> 
>>> [1]
>>> https://datatracker.ietf.org/doc/draft-cheng-lsr-isis-srv6-sid-block/
>>> <https://datatracker.ietf.org/doc/draft-cheng-lsr-isis-srv6-sid-block/>
>>> 
>>> 
>>> 
>>> Thanks,
>>> 
>>> Weiqiang Cheng
>>> 
>>> 
>>> 
>>>     ----邮件原文----
>>>     *发件人:*Louis Chan  <[email protected]>
>>>     *收件
>>>     人:*"Les Ginsberg (ginsberg)" <[email protected]>,Acee Lindem 
>>> <[email protected]>
>>>     *抄 送:
>>>     *lsr  <[email protected]>,Krzysztof Szarkowicz  
>>> <[email protected]>,Weiqiang Cheng  <[email protected]>
>>>     *发送时间:*2023-04-12 10:45:56
>>>     *主题:*Re: [Lsr] IETF-
>>>     116 LSR - IGP extensions for Advertising Offset forFlex-Algorithm
>>> 
>>>     Hi Les,
>>> 
>>>     Thanks for the prompt reply. Please see inline for clarification [lc2].
>>> 
>>>     /Louis
>>> 
>>>     *From:* Les Ginsberg (ginsberg) <[email protected]>
>>>     *Sent:* Tuesday, April 11, 2023 11:03 PM
>>>     *To:* Louis Chan <[email protected]>; Acee Lindem <[email protected]>
>>>     *Cc:* lsr <[email protected]>; Krzysztof Szarkowicz
>>>     <[email protected]>; Weiqiang Cheng
>>>     <[email protected]>
>>>     *Subject:* RE: [Lsr] IETF-116 LSR - IGP extensions for Advertising
>>>     Offset for Flex-Algorithm
>>> 
>>>     *[External Email. Be cautious of content]*
>>> 
>>>     Louis -
>>> 
>>>     Please see inline.
>>> 
>>>      > -----Original Message-----
>>> 
>>>      > From: Louis Chan <[email protected] <mailto:[email protected]>>
>>> 
>>>      > Sent: Monday, April 10, 2023 11:01 PM
>>> 
>>>      > To: Les Ginsberg (ginsberg) <[email protected]
>>>     <mailto:[email protected]>>; Acee Lindem
>>> 
>>>      > <[email protected] <mailto:[email protected]>>
>>> 
>>>      > Cc: lsr <[email protected] <mailto:[email protected]>>; Krzysztof
>>>     Szarkowicz <[email protected] <mailto:[email protected]>>;
>>> 
>>>      > Weiqiang Cheng <[email protected]
>>>     <mailto:[email protected]>>
>>> 
>>>      > Subject: RE: [Lsr] IETF-116 LSR - IGP extensions for Advertising
>>>     Offset for
>>> 
>>>      > Flex-Algorithm
>>> 
>>>      >
>>> 
>>>      > Hi Les,
>>> 
>>>      >
>>> 
>>>      > Thanks for your questions. Please see inline [lc] below.
>>> 
>>>      >
>>> 
>>>      > /Louis
>>> 
>>>      >
>>> 
>>>      > -----Original Message-----
>>> 
>>>      > From: Les Ginsberg (ginsberg) <[email protected]
>>>     <mailto:[email protected]>>
>>> 
>>>      > Sent: Saturday, April 8, 2023 7:34 AM
>>> 
>>>      > To: Acee Lindem <[email protected]
>>>     <mailto:[email protected]>>; Louis Chan <[email protected]
>>>     <mailto:[email protected]>>
>>> 
>>>      > Cc: lsr <[email protected] <mailto:[email protected]>>
>>> 
>>>      > Subject: RE: [Lsr] IETF-116 LSR - IGP extensions for Advertising
>>>     Offset for
>>> 
>>>      > Flex-Algorithm
>>> 
>>>      >
>>> 
>>>      > [External Email. Be cautious of content]
>>> 
>>>      >
>>> 
>>>      >
>>> 
>>>      > OK - since Acee opened the door - here are some comments from me -
>>> 
>>>      > starting with the most important.
>>> 
>>>      >
>>> 
>>>      > (BTW - I still have limited enthusiasm for this draft.)
>>> 
>>>      >
>>> 
>>>      > 1)The proposal places some restrictions on how operators
>>>     provision their
>>> 
>>>      > network in terms of assigning SIDs and reserving space for future
>>> 
>>>      > assignments.
>>> 
>>>      > If operators do not use compatible assignment schemes, then this
>>>     will never
>>> 
>>>      > get deployed. It is therefore not enough to come with a nice idea
>>>     - you must
>>> 
>>>      > have some enthusiasm from the operator community.
>>> 
>>>      >
>>> 
>>>      >
>>> 
>>>      > [lc] If the operator only wants to deploy flex-algo, there is no
>>>     change in their
>>> 
>>>      > Node-sid numbering scheme. For the Adj-sid, these are local
>>>     labels with local
>>> 
>>>      > significant only, and there is no need for any special planning
>>>     for Adj-sid,
>>> 
>>>      > unless you are suggesting they want to make fixed assignment of
>>>     Adj-sid
>>> 
>>>      > label for each link. Even with fixed, the proposed draft has
>>>     benefit on that. I
>>> 
>>>      > will explain later.
>>> 
>>>      >
>>> 
>>>     [LES:] Let's discuss this in the context of prefix-sids - the same
>>>     applies to adj-sids.
>>> 
>>>     Today (i.e., in the absence of your proposal) an operator is free to
>>>     assign any label within the SRGB for a given prefix/algo pair so
>>>     long as it is not assigned to some other prefix/algo context.
>>> 
>>>     Your proposal places some new restrictions. Now, for a given
>>>     flex-algo, whenever an operator assigns a given label for a prefix
>>>     in Algo 0 (call it Label-A0), they must guarantee that
>>>     "Label-A0+offset" for an  advertised flex-algo specific offset is
>>>     available to be assigned for the prefix/flex-algo pair - and this
>>>     must be true for all prefixes advertised in algo 0.
>>> 
>>>     This is certainly possible to do, but is not guaranteed to be the
>>>     case in current deployments.
>>> 
>>>     For example - and this is only an example...today an operator might
>>>     utilize a provisioning tool to assign prefix-sids for all supported
>>>     algorithms on all nodes in the network.
>>> 
>>>     To do this, the tool might maintain a database of assigned labels.
>>>     When provisioning a new node/prefix/algorithm, the logic in the tool
>>>     might simply take the next available label in the database.
>>> 
>>>     The result of this would not be consistent with the requirements of
>>>     your draft.
>>> 
>>>     Which is why I say in order to deploy the extension you propose,
>>>     such an operator would have to modify its provisioning tool.
>>> 
>>>     [lc2] There might be some misunderstanding of our proposal. Let me
>>>     give some examples.
>>> 
>>>     Case 1: Flex-Algo only
>>> 
>>>     Prefix offset advertisement: “no”
>>> 
>>>     Adj-sid offset advertisement: yes
>>> 
>>>     In slide 8’s example, FA129 is using label “402001”, and the
>>>     advertisement of this label is using existing methods.
>>> 
>>>     e.g. SRGB = 400000-460000
>>> 
>>>     FA129: index 2001 (preferred value), or one can choose 111, 222
>>> 
>>>     FA130 (new): index 3001 (preferred value), or 333, 4444
>>> 
>>>     This does not change how the operator to assign label for prefix-sid
>>>     with their current method. Any index/label could be used for FA
>>>     prefix within SRGB.
>>> 
>>>     The only change is the Adj-sid label allocation, but this “mostly”
>>>     is  only “local” to one node. There is no effect on global label
>>>     allocation.
>>> 
>>>     This draft will be compatible to what operators are doing today.
>>> 
>>>     Case 2: VFA only
>>> 
>>>     Prefix offset advertisement: yes
>>> 
>>>     Adj-sid offset advertisement: yes
>>> 
>>>     I agree, with VFA, there would be impact to global allocation to
>>>     node-sid/prefix-sid. But VFA is a totally new concept. No one has
>>>     deployed that yet.
>>> 
>>>     There is no impact to operators which stick to deploy only Flex-algo.
>>> 
>>>     Other case: Flex-Algo w/o Adj-sid offset
>>> 
>>>                    Continue the example of Case#1 above
>>> 
>>>                    Another FA131 is added, but no Adj-sid offset is
>>>     advertised
>>> 
>>>                    The question would be
>>> 
>>>       *
>>> 
>>>         Either allow this configuration, and FA131 will fallback using
>>>         Algo 0’s  adj-sid
>>> 
>>>       *
>>> 
>>>         Or, disallow this configuration
>>> 
>>>     I tend to “allow” such configuration with mix of FA129, FA130 (with
>>>     adj-sid offset) and FA131 (w/o adj-sid offset)
>>> 
>>>     [/lc2]
>>> 
>>>     Could this be done? Sure.
>>> 
>>>     Do operators want to do this? I do not know.
>>> 
>>>     But since this would be necessary in order to use your proposed
>>>     extension, it is necessary to gauge operator enthusiasm for making
>>>     such changes in order to know whether there is any point in
>>>     proceeding with  your proposal.
>>> 
>>>      > In slide 8 of the below presentation
>>> 
>>>      >
>>>     
>>> https://datatracker.ietf.org/meeting/116/materials/slides-116-lsr-03-ietf116-
>>>  
>>> <https://urldefense.com/v3/__https:/datatracker.ietf.org/meeting/116/materials/slides-116-lsr-03-ietf116-igp-adv-offset-01__;!!NEt6yMaO-gk!Bl7Swe9ql9VT0qGkD6FoZZzTWT2fmIx55eSncdmMgoCJetJ5-80micuqnqk79yewGB-BleOfrYpSjfI$>
>>> 
>>>     >  igp-adv-offset-01
>>>     
>>> <https://urldefense.com/v3/__https:/datatracker.ietf.org/meeting/116/materials/slides-116-lsr-03-ietf116-igp-adv-offset-01__;!!NEt6yMaO-gk!Bl7Swe9ql9VT0qGkD6FoZZzTWT2fmIx55eSncdmMgoCJetJ5-80micuqnqk79yewGB-BleOfrYpSjfI$>
>>> 
>>>      >
>>> 
>>>      > FA129 is a prefix-sid (400201) allocated by operator, and it can
>>>     be any label.
>>> 
>>>      > There is no connection to how Adj-sid is derived.
>>> 
>>>      > Per Flex-Algo adj-sid assignment is not affecting network wide label
>>> 
>>>      > assignment from operation perspective. Each node could have
>>>     different local
>>> 
>>>      > block for such adj-sid assignment. One might need to estimate
>>>     total possible
>>> 
>>>      > number of link in one chassis for such allocation, or it could be
>>>     estimated by
>>> 
>>>      > OS software itself. I also mentioned in the session, if there is
>>>     100 x FA with
>>> 
>>>      > 1000 links (high end), it is only 100k labels. Is it difficult to
>>>     allocate such.
>>> 
>>>     [LES:] Your proposal does not reduce the number of labels which need
>>>     to be "allocated" and installed in forwarding, it only reduces the
>>>     number of bytes used to advertise this information in LSPs/LSAs.
>>> 
>>>     [lc2] You are correct.
>>> 
>>>     I think, at the same time, it helps reducing time for global
>>>     convergence since the advertisement size is smaller, especially in
>>>     network with long diameter with multi-hops.
>>> 
>>>     Also, in
>>>     https://datatracker.ietf.org/doc/draft-ietf-lsr-isis-fast-flooding/
>>>     <https://datatracker.ietf.org/doc/draft-ietf-lsr-isis-fast-flooding/>  
>>> (which you participated in)
>>> 
>>>      >>>
>>> 
>>>        As IS-IS is deployed in greater scale both in the number of nodes in
>>> 
>>>         an area and in the number of neighbors per node, the impact of the
>>> 
>>>         historic flooding rates becomes more significant.  Consider the
>>> 
>>>         bringup or failure of a node with 1000 neighbors.  This will result
>>> 
>>>         in a minimum of 1000 LSP updates.  At typical LSP flooding rates
>>>     used
>>> 
>>>         today (33 LSPs/second), it would take 30+ seconds simply to send the
>>> 
>>>         updated LSPs to a given neighbor.  Depending on the diameter of the
>>> 
>>>         network, achieving a consistent LSDB on all nodes in the network
>>> 
>>>         could easily take a minute or more.
>>> 
>>>     <<<
>>> 
>>>     This proposed draft will certainly help.
>>> 
>>>     [/lc2]
>>> 
>>>      >
>>> 
>>>      > So, this is why I do not understand your question in full.
>>> 
>>>      >
>>> 
>>>      > If the operator plans to use VFA, that would be a different
>>>     discussion. VFA,
>>> 
>>>      > today, does not exist in deployment.
>>> 
>>>      >
>>> 
>>>     [LES:] My comments here have nothing to do with VFA.
>>> 
>>>      > [/lc]
>>> 
>>>      >
>>> 
>>>      > Have you discussed this idea with any operators?
>>> 
>>>      >
>>> 
>>>      > [lc] I include Wei-qiang from China mobile in this thread. He has
>>>     shown his
>>> 
>>>      > need on this kind of solution. Maybe, he could give his
>>>     perspective here. [/lc]
>>> 
>>>      >
>>> 
>>>      > If so, what has been their response?
>>> 
>>>      > If they are open to the idea, how might they migrate from their
>>>     existing
>>> 
>>>      > assignment schemes to an assignment scheme compatible with the
>>> 
>>>      > proposal?
>>> 
>>>      >
>>> 
>>>      > These are questions that need to be answered before considering
>>>     this idea.
>>> 
>>>      >
>>> 
>>>      > [lc] In slide 8, if you see these label numbers
>>> 
>>>      >
>>> 
>>>      > Prefix-sid: 400001, 402001, 406001, 407001
>>> 
>>>      > Adj-sid: 32, 2032, 6032, 7032
>>> 
>>>      >
>>> 
>>>      > From operator perspective or troubleshooting perspective, value
>>>     xxx001
>>> 
>>>      > represent the same node, and value x032 represent the same link. This
>>> 
>>>      > makes things more organized and easier to understand.
>>> 
>>>      >
>>> 
>>>      > If all are random labels, I do not see any benefit at all.
>>> 
>>>      > [/lc]
>>> 
>>>     [LES:] I am not commenting on whether the label assignment scheme
>>>     you propose is better or worse than any other.
>>> 
>>>     I am only pointing out that you are imposing new restrictions on how
>>>     labels are allocated.
>>> 
>>>     As you are not in charge of how operators provision their networks
>>>     (nor am I), it is presumptuous of you to think that simply because
>>>     you think this is a better way to do things that operators will be
>>>     happy to modify their existing networks  to conform to your proposed
>>>     restrictions.
>>> 
>>>     This isn’t academia - you need to vet this with the operator community.
>>> 
>>>     [lc2] Please refer to the examples at the top. The picture should be
>>>     clear by now. There is no restriction to what is deployed today. [/lc2]
>>> 
>>>      >
>>> 
>>>      > 2)Section 5 Compatibilty
>>> 
>>>      >
>>> 
>>>      > There is no "compatibility" with legacy nodes - because all nodes
>>>     in the
>>> 
>>>      > network have to have a consistent understanding of what SID is
>>>     assigned to a
>>> 
>>>      > given context (for prefixes and adjacencies) since they might
>>>     need to install
>>> 
>>>      > forwarding entries for that context.
>>> 
>>>      > I do not see any point in deploying this until all nodes support
>>>     it. If you did do
>>> 
>>>      > so, you would need to advertise old and new forms - which does the
>>> 
>>>      > opposite of what you are trying to achieve. Instead of reducing
>>>     LSP space
>>> 
>>>      > used you would increase it.
>>> 
>>>      >
>>> 
>>>      > [lc] If the operator just plans to use only Flex-Algo, and no
>>>     VFA, it should be
>>> 
>>>      > compatible with legacy implementation. If legacy nodes do not
>>>     understand
>>> 
>>>      > adj-sid offset notation, these nodes could just ignore it. The
>>>     forwarding
>>> 
>>>      > plane should work with co-existence of old and new nodes. Per
>>>     flex-algo adj-
>>> 
>>>      > sid is only local significant to one node. New nodes should
>>>     detect whether
>>> 
>>>      > legacy nodes exist in the network via such new extension
>>>     advertisement.
>>> 
>>>      > And new nodes should use only algo 0 adj-sid from legacy nodes
>>>     for any TI-
>>> 
>>>      > LFA.
>>> 
>>>     [LES:] Consider a network of 100 nodes.
>>> 
>>>     Let's say the "left-hand-side" of the network consist of legacy
>>>     nodes who do not understand your new advertisements.
>>> 
>>>     The "right-hand-side" of the network consists of upgraded nodes who
>>>     support the new advertisements.
>>> 
>>>     Consider nodes PE-LEFT and PE-RIGHT.
>>> 
>>>     PE-RIGHT advertises a prefix-SID of 1000 for 2.2.2.2/32, and an
>>>     offset of 1000 for flex-algo 128.
>>> 
>>>     PE-LEFT supports flex-algo 128 and wants to install a forwarding
>>>     entry for 2.2.2.2 for flex-algo 128.
>>> 
>>>     It looks in the LSPs originated by PE-RIGHT. It does not see any
>>>     assigned SID for 2.2.2.2/32 flex-algo 128.
>>> 
>>>     It cannot create a forwarding entry. And neither can any other node
>>>     in the left hand side of the network.
>>> 
>>>     When PE-RIGHT stops advertising the explicit prefix SID for
>>>     2.2.2.2/32 Algo 128, all legacy nodes are unable to create
>>>     forwarding entries for the prefix/algo tuple.
>>> 
>>>     This isn’t backwards compatible. 
>>> 
>>>     In general, you cannot advertise information legacy nodes require in
>>>     a new container that legacy nodes do not understand and claim that
>>>     you are backwards compatible.
>>> 
>>>     [lc2] Please refers to the examples for clarification.
>>> 
>>>      1.
>>> 
>>>         For existing Flex-Algo deployment, it would be compatible. There
>>>         is no change in the container format on how prefix-sid
>>>         2.2.2.2/32 in FA128 is advertised.
>>> 
>>>      1.
>>> 
>>>         For new VFA, it would not be compatible. But….it does not mean
>>>         that we could not have VFA running in the same network.
>>> 
>>>     There could be procedures to enhance such. With your example, one
>>>     workaround could be:
>>> 
>>>     For VFA 600, PE-RIGHT detects that PE-LEFT does not participate in
>>>     VFA600 (due to no offset advertisement seen),
>>> 
>>>       *
>>> 
>>>         Either, it spawns new CSPF for VFA600 instead of sharing FA129’s
>>>         result. Bypass PE-LEFT as a result.
>>> 
>>>       *
>>> 
>>>         Or, it uses legacy node FA129 prefix-sid and adj-sid as
>>>         replacement (note: this method needs more comment)
>>> 
>>>     In either ways, VFA600 could work without issue even with legacy
>>>     nodes co-existence.
>>> 
>>>     After PE-LEFT upgraded, VFA600 would be using FA129 CSPF result
>>>     instead, and save CPU resources in each node.
>>> 
>>>     Another question: do we need FAD for VFA600? Currently, no. Not
>>>     mandatory.
>>> 
>>>     But it could be considered if “good to have” parameters are passed
>>>     along with FAD.
>>> 
>>>     [/lc2]
>>> 
>>>      >
>>> 
>>>      > I do not see a major problem. Please give me an example to
>>>     illustrate your
>>> 
>>>      > concern if possible.
>>> 
>>>      >
>>> 
>>>      > Of course, we need to do double check on the claim and possibly lab
>>> 
>>>      > verification to see if the backward compatibility could be
>>>     achieved. It could
>>> 
>>>      > be vendor specific.
>>> 
>>>      >
>>> 
>>>      > [/lc]
>>> 
>>>      >
>>> 
>>>      >
>>> 
>>>      > What does deserve discussion is a "hitless migration strategy".
>>>     When full
>>> 
>>>      > support is available, if you were to switch to the new scheme,
>>>     you would
>>> 
>>>      > want to do so without changing any existing SIDs as this would avoid
>>> 
>>>      > forwarding disruption. Which means operators would have to modify
>>>     their
>>> 
>>>      > SID assignment scheme in advance of deploying the new scheme.
>>> 
>>>      >
>>> 
>>>      > [lc] For VFA, there would be issue for legacy nodes. I agree. In
>>>     this case,
>>> 
>>>      > solution could be
>>> 
>>>      >         - either have a fallback plan for newer nodes if
>>>     detection of legacy nodes
>>> 
>>>      > exist in the network. E.g. spawn new CSPF
>>> 
>>>      >         - or, totally not to deploy VFA unless all nodes are
>>>     upgraded.
>>> 
>>>      >
>>> 
>>>      > Section 5 is not updated with VFA inclusion.
>>> 
>>>     [LES:] My comments have nothing to do with VFA.
>>> 
>>>     Please reconsider them after you have understood the backwards
>>>     compatibility issues.
>>> 
>>>      >
>>> 
>>>      > [/lc]
>>> 
>>>      >
>>> 
>>>      > 3)Virtual Flex Algorithm
>>> 
>>>      >
>>> 
>>>      > You have introduced a new concept with very little explanation of
>>>     what it is
>>> 
>>>      > nor how it can be supported.
>>> 
>>>      > For example, how would we determine which nodes support a given VFA?
>>> 
>>>      > Since the algorithm value must be greater than 255, it cannot be
>>>     advertised in
>>> 
>>>      > the existing SR Algorithm sub-TLV.
>>> 
>>>      >
>>> 
>>>      > If you are serious about this idea, please provide a more complete
>>> 
>>>      > discussion.
>>> 
>>>      >
>>> 
>>>      > [lc] We could illustrate application examples in next
>>>     presentation. For
>>> 
>>>      > ethernet, we have port, and then we have VLAN and stacked vlan.
>>>     History
>>> 
>>>      > has some hints on this.
>>> 
>>>      >
>>> 
>>>     [LES:] You are writing a normative specification. Hoping that all
>>>     readers/implementors have the same "intuition" isn’t sufficient.
>>> 
>>>         Les
>>> 
>>>      > [/lc]
>>> 
>>>      >
>>> 
>>>      > 4)Section 4.3
>>> 
>>>      >
>>> 
>>>      > "R" and "N" flags are now defined in prefix attributes sub-TLV
>>>     (RFC7794)
>>> 
>>>      > They were originally defined in the SR sub-TLV because RFC 7794
>>>     did not exist
>>> 
>>>      > at the time.
>>> 
>>>      > The only reason they continue to exist in RFC 8667 is for backwards
>>> 
>>>      > compatibility with early implementation of SR-MPLS based on early
>>>     drafts of
>>> 
>>>      > what became RFC 8667.
>>> 
>>>      > Please do not introduce them in new sub-TLVs - there is no need.
>>> 
>>>      >
>>> 
>>>      > [lc] noted with thanks [/lc]
>>> 
>>>      >
>>> 
>>>      > 5)ADJ-SIDs are NOT allocated from the SRGB as they are local in
>>>     scope.
>>> 
>>>      > They MAY be allocated from the SRLB - or outside either GB range.
>>> 
>>>      > Please correct the document in this regard.
>>> 
>>>      >
>>> 
>>>      > [lc] noted [/lc]
>>> 
>>>      >
>>> 
>>>      >    Les
>>> 
>>>      >
>>> 
>>>      > > -----Original Message-----
>>> 
>>>      > > From: Lsr <[email protected] <mailto:[email protected]>>
>>>     On Behalf Of Acee Lindem
>>> 
>>>      > > Sent: Friday, April 7, 2023 11:43 AM
>>> 
>>>      > > To: Louis Chan <[email protected] <mailto:[email protected]>>
>>> 
>>>      > > Cc: lsr <[email protected] <mailto:[email protected]>>
>>> 
>>>      > > Subject: Re: [Lsr] IETF-116 LSR - IGP extensions for Advertising
>>> 
>>>      > > Offset for Flex-Algorithm
>>> 
>>>      > >
>>> 
>>>      > > Hi Louis,
>>> 
>>>      > >
>>> 
>>>      > > In the interest of initiating discussion, I would like to
>>>     propose the
>>> 
>>>      > > term "Flex Algorithm Traffic Class (FATC)" for the sub-division of
>>> 
>>>      > > flex-algorithm traffic referred to in the draft as “Virtual
>>>     Flex Algorithm”.
>>> 
>>>      > >
>>> 
>>>      > > Also, in your terminology, you refer referred to TLVs and
>>>     fields with
>>> 
>>>      > > simply “Algorithm” when RFC 9350 uses “Flex Algorithm”.
>>> 
>>>      > >
>>> 
>>>      > > Thanks,
>>> 
>>>      > > Acee
>>> 
>>>      > >
>>> 
>>>      > >
>>> 
>>>      > >
>>> 
>>>      > > _______________________________________________
>>> 
>>>      > > Lsr mailing list
>>> 
>>>      > > [email protected] <mailto:[email protected]>
>>> 
>>>      > >
>>>     https://urldefense.com/v3/__https://www.ietf.org/mailman/listinfo/lsr_ 
>>> <https://urldefense.com/v3/__https:/www.ietf.org/mailman/listinfo/lsr_>
>>> 
>>>      > > _;!!NEt6yMaO-gk!B9ufrV6k-
>>> 
>>>      > c7mtP9JUiXbrF3NCkZ15_UMLBjV_fnJovfz18M5VkkI2F
>>> 
>>>      > > EoixpkxsfMnbqwbR0bpHgoS9E$
>>> 
>>>      >
>>> 
>>>      > Juniper Business Use Only
>>> 
>>>     Juniper Business Use Only
>>> 
>>> 
>>>     Juniper Business Use Only
>>> 
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