Re: [Lsr] IETF-116 LSR - IGP extensions for AdvertisingOffsetforFlex-Algorithm

[Louis Chan <[e-mail]>]

Hi Liyan,

Thanks for the input.

Flex-Algo is supported by majority of vendors. The interoperability effort is less compared to a new agreed forwarding plane, which takes time.

I always believe: More is less. Less is more

/Louis

From: Liyan Gong <[e-mail]>
Sent: Thursday, April 13, 2023 12:50 PM
To: Louis Chan <[e-mail]>; Ketan Talaulikar <[e-mail]>
Cc: Krzysztof Szarkowicz <[e-mail]>; Robert Raszuk <[e-mail]>; linchangwang <[e-mail]>; Acee Lindem <[e-mail]>; Peter Psenak <[e-mail]>; 程伟强 <[e-mail]>; Les Ginsberg(ginsbe <[e-mail]>; lsr <[e-mail]>
Subject: Re:Re: [Lsr] IETF-116 LSR - IGP extensions for AdvertisingOffsetforFlex-Algorithm

[External Email. Be cautious of content]


Hi All，

Thanks for your discussion, here are some informations to help understanding better.

1. About the application scenario, please refer to the following draft.

https://datatracker.ietf.org/doc/draft-gong-teas-hierarchical-slice-solution/<https://urldefense.com/v3/__https:/datatracker.ietf.org/doc/draft-gong-teas-hierarchical-slice-solution/__;!!NEt6yMaO-gk!FSBvm2aTbXiqd9L2oPCuW4qX1B2Z7HlXTd1s3sXMsnYLZkZgYIv1m2kWSyMieBZZh58x5f14cN1ZaWfUJ4OGrA$>

Flex-Algo can be associated with the level-1 network slice which provides dynamic programming topology.

The number of Flex-Algos is the same as the number of the level-1 network slices. Maybe it can reach dozens.



2. About the performance impact, Maybe we can think of it as advertising massive routes through multi-pair neighbors in IGP domain.

Since the advertising and flooding process occupy a lot of router resources, Network changes can not be converged in time.

This will result in wrong traffic forwarding. That is why there is limitation on the number of routes in IGP domain.

According to the anaysis by Changwang in the following email, SIDs take up a big part.

We think it is better if Flex-Algo can be scaled up by optimizing the SIDs format without changing the IGP basic mechanism.



Best Regards,

Liyan





----邮件原文----
发件人：Louis Chan  <louisc=[e-mail]<mailto:louisc=[e-mail]>>
收件人：Ketan Talaulikar  <[e-mail]<mailto:[e-mail]>>
抄　送: Krzysztof Szarkowicz  <[e-mail]<mailto:[e-mail]>>,Robert Raszuk <[e-mail]<mailto:[e-mail]>>,linchangwang  <[e-mail]<mailto:[e-mail]>>,Acee Lindem <[e-mail]<mailto:[e-mail]>>,Peter Psenak  <[e-mail]<mailto:[e-mail]>>,"程伟强" <[e-mail]<mailto:[e-mail]>>,"Les Ginsberg(ginsbe" <[e-mail]<mailto:[e-mail]>>,lsr  <[e-mail]<mailto:[e-mail]>>
发送时间：2023-04-13 12:31:12
主题：Re: [Lsr] IETF-116 LSR - IGP extensions for Advertising OffsetforFlex-Algorithm


Hi Ketan,

Just a short response.

If you remember ATM days, there are VP shaping/policing and VC shaping/policing. It can solve quite complicated QOS problem.
Here we are not doing the costly ATM again.

With kind of hierarchical QOS readily available in ASIC today, it potentially solves some complex multipoint to multipoint QOS problem.
But first, it requires labeling the packet, like VCI and VPI.

I am going to stop here because it would be too much to discuss.

Rgds
Louis

From: Ketan Talaulikar <[e-mail]<mailto:[e-mail]>>
Sent: Thursday, April 13, 2023 12:02 PM
To: Louis Chan <[e-mail]<mailto:[e-mail]>>
Cc: Krzysztof Szarkowicz <[e-mail]<mailto:[e-mail]>>; Robert Raszuk <[e-mail]<mailto:[e-mail]>>; linchangwang <[e-mail]<mailto:[e-mail]>>; Acee Lindem <[e-mail]<mailto:[e-mail]>>; Peter Psenak <[e-mail]<mailto:[e-mail]>>; 程伟强 <[e-mail]<mailto:[e-mail]>>; Les Ginsberg (ginsbe <[e-mail]<mailto:[e-mail]>>; lsr <[e-mail]<mailto:[e-mail]>>
Subject: Re: [Lsr] IETF-116 LSR - IGP extensions for Advertising Offset forFlex-Algorithm

[External Email. Be cautious of content]

Hi Louis,

First we need to ascertain if it is necessary before we get things flooded into IGPs. Then we can get to the evaluation of whether or how "evil" it is.

The VLAN analogy seems incorrect to me and a debate on that may be orthogonal to this topic. I'll wait for the "necessity" to be first described before taking a bite at this PIZZA ;-)

Once again, thanks for your work on this document.

Thanks,
Ketan

On Thu, Apr 13, 2023 at 9:15AM Louis Chan <[e-mail]<mailto:[e-mail]>> wrote:
Hi Ketan,

First, I like “PIZZA” more than “VFA”, and at least it is closer to “real” and tasty instead of “virtual” and boring. :)

For VFA, it is just a further identification method. History has VLAN first introduced in ethernet. People might think it was already enough in that period. But later, market asked  for stacked vlan, and find its application.

Having VFA/PIZZA might give more possibilities for future usage. It is only ~30B advertisement per VFA per node, and it would not be a big harm. And there is no further header overhead  (or cell tax) in forwarding plane, and make it easy of vendor interop. This is more important.

I have no intention to swamp IGP with control plane kind of info, like QOS profile.  My view is to leave IGP as slim as possible for quick reaction to network changes.

If it is a necessary evil, it should be minimum. My take would be getting minimum but useful enough info into FAD. In this case, the advertisement size is small, with ease of management.   That is what I refer to “good to have” info in previous email.

Rgds
Louis

From: Ketan Talaulikar <[e-mail]<mailto:[e-mail]>>
Sent: Thursday, April 13, 2023 12:06 AM
To: Krzysztof Szarkowicz <[e-mail]<mailto:[e-mail]>>
Cc: Robert Raszuk <[e-mail]<mailto:[e-mail]>>; linchangwang <[e-mail]<mailto:[e-mail]>>; Acee Lindem <[e-mail]<mailto:[e-mail]>>;  Peter Psenak <[e-mail]<mailto:[e-mail]>>; 程伟强 <[e-mail]<mailto:[e-mail]>>; Louis Chan <[e-mail]<mailto:[e-mail]>>;  Les Ginsberg (ginsbe <[e-mail]<mailto:[e-mail]>>; lsr <[e-mail]<mailto:[e-mail]>>
Subject: Re: [Lsr] IETF-116 LSR - IGP extensions for Advertising Offset forFlex-Algorithm

[External Email. Be cautious of content]

Hi Krzysztof,

I got the impression that the use-case/need for these VFA SIDs in the first place was to carry some indication in the packet for local treatment at each hop (e.g,, bandwidth profile  or QoS treatment?) in the data path since the forwarding is based on FlexAlgo.

If not, then I am not sure that I follow the use-case or motivation for VFA (or pizza ;-) as Louis calls it) in the first place.

Thanks,
Ketan


On Wed, Apr 12, 2023 at 9:28PM Krzysztof Szarkowicz <[e-mail]<mailto:[e-mail]>> wrote:
Hi Ketan,

I agree with you. The draft doesn’t propose to carry ’service bandwidth profile’ parameters in the IGP.

The draft is dealing only with label/SID assignment/generation and distribution.

Thanks,
Krzysztof


On 2023 -Apr-12, at 17:49, Ketan Talaulikar <[e-mail]<mailto:[e-mail]>> wrote:


[External Email. Be cautious of content]


Hi Krzysztof,

A further question is if it is necessary to carry this "service bandwidth profile" information in the IGPs in the first place. Why not indicate this just in the packet? Wouldn't  that be a better way to help scale IGPs by not introducing this into IGPs in the first place? ;-)

One such simple solution is proposed by https://datatracker.ietf.org/doc/draft-decraene-mpls-slid-encoded-entropy-label-id/<https://urldefense.com/v3/__https:/datatracker.ietf.org/doc/draft-decraene-mpls-slid-encoded-entropy-label-id/__;!!NEt6yMaO-gk!DxCsNxydz3b_s_iNl0j_6pyHLD1_vLYmeqwZbd_OBYdhfs3BBaQ8bIXbBsB-4Yigax-NkpPUA1EmCDwYmDNrSqU0Lg$>

Thanks,
Ketan


On Wed, Apr 12, 2023 at 9:13PM Krzysztof Szarkowicz <kszarkowicz=[e-mail]<mailto:[e-mail]>> wrote:
Hi,

It is the question, if we could for example have more than 20 (e.g. 200), for 200 different service bandwidth guarantees (but having only one - or handful - SPF calculation domains,  where one SPF calculation domain is one ‘legacy’ flex-algo ). The challenge is with SPP calculations, once the number of flex-algos goes high.

Thanks,
Krzysztof


On 2023 -Apr-12, at 17:13, Robert Raszuk <[e-mail]<mailto:[e-mail]>> wrote:


[External Email. Be cautious of content]



Ok you can use 20 flex algos today with no extension. Is going to another level of nesting really necessary ?

On Wed, Apr 12, 2023 at 4:52PM linchangwang <[e-mail]<mailto:[e-mail]>> wrote:
Hi Acee

An operator's backbone network is divided into different flex algorithms planes according to different SLA requirements of users.
A flex algo represents a service requirement, such as bandwidth requirements.
20 flex algorithms represent 20 different service bandwidth guarantees, corresponding to different resource requirements.

Thanks,
Changwang lin

From: Acee Lindem [mailto:[e-mail]<mailto:[e-mail]>]
Sent: Wednesday, April 12, 2023 10:12 PM
To: Peter Psenak
Cc: linchangwang (RD); 程伟强; Louis Chan; Les Ginsberg (ginsbe; lsr; Krzysztof Szarkowicz
Subject: Re: [Lsr] IETF-116 LSR - IGP extensions for Advertising Offset forFlex-Algorithm

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 <[e-mail]<mailto:[e-mail]>> 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:[e-mail]<mailto:[e-mail]>] 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://urldefense.com/v3/__https:/datatracker.ietf.org/doc/draft-cheng-lsr-isis-srv6-sid-block/__;!!NEt6yMaO-gk!GCoxXhuL7ryqRodFUI2f-GPQa1_Vjs9WLIB_XJtQUiKVcm6Yrxqx5p-_PmGOQFNseVacNf7mx4QUND7v7my7$>
<https://datatracker.ietf.org/doc/draft-cheng-lsr-isis-srv6-sid-block/<https://urldefense.com/v3/__https:/datatracker.ietf.org/doc/draft-cheng-lsr-isis-srv6-sid-block/__;!!NEt6yMaO-gk!GCoxXhuL7ryqRodFUI2f-GPQa1_Vjs9WLIB_XJtQUiKVcm6Yrxqx5p-_PmGOQFNseVacNf7mx4QUND7v7my7$>>



Thanks,

Weiqiang Cheng



    ----邮件原文----
    *发件人：*Louis Chan  <louisc=[e-mail]<mailto:[e-mail]>>
    *收件
    人：*"Les Ginsberg (ginsberg)" <[e-mail]<mailto:[e-mail]>>,Acee  Lindem <[e-mail]<mailto:[e-mail]>>
    *抄　送:
    *lsr  <[e-mail]<mailto:[e-mail]>>,Krzysztof Szarkowicz  <[e-mail]<mailto:[e-mail]>>,Weiqiang Cheng  <[e-mail]<mailto:[e-mail]>>
    *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) <[e-mail]<mailto:[e-mail]>>
    *Sent:* Tuesday, April 11, 2023 11:03 PM
    *To:* Louis Chan <[e-mail]<mailto:[e-mail]>>; Acee Lindem <[e-mail]<mailto:[e-mail]>>
    *Cc:* lsr <[e-mail]<mailto:[e-mail]>>; Krzysztof Szarkowicz
    <[e-mail]<mailto:[e-mail]>>; Weiqiang Cheng
    <[e-mail]<mailto:[e-mail]>>
    *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 <[e-mail]<mailto:[e-mail]> <mailto:[e-mail]<mailto:[e-mail]>>>

     > Sent: Monday, April 10, 2023 11:01 PM

     > To: Les Ginsberg (ginsberg) <[e-mail]<mailto:[e-mail]>
    <mailto:[e-mail]<mailto:[e-mail]>>>; Acee Lindem

     > <[e-mail]<mailto:[e-mail]> <mailto:[e-mail]<mailto:[e-mail]>>>

     > Cc: lsr <[e-mail]<mailto:[e-mail]> <mailto:[e-mail]<mailto:[e-mail]>>>; Krzysztof
    Szarkowicz <[e-mail]<mailto:[e-mail]> <mailto:[e-mail]<mailto:[e-mail]>>>;

     > Weiqiang Cheng <[e-mail]<mailto:[e-mail]>
    <mailto:[e-mail]<mailto:[e-mail]>>>

     > 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) <[e-mail]<mailto:[e-mail]>
    <mailto:[e-mail]<mailto:[e-mail]>>>

     > Sent: Saturday, April 8, 2023 7:34 AM

     > To: Acee Lindem <[e-mail]<mailto:[e-mail]>
    <mailto:[e-mail]<mailto:[e-mail]>>>; Louis Chan <[e-mail]<mailto:[e-mail]>
    <mailto:[e-mail]<mailto:[e-mail]>>>

     > Cc: lsr <[e-mail]<mailto:[e-mail]> <mailto:[e-mail]<mailto:[e-mail]>>>

     > 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-__;!!NEt6yMaO-gk!GCoxXhuL7ryqRodFUI2f-GPQa1_Vjs9WLIB_XJtQUiKVcm6Yrxqx5p-_PmGOQFNseVacNf7mx4QUNBlx2nlh$>  <https://urldefense.com/v3/__https:/datatracker.ietf.org/meeting/116/materials/slides-116-lsr-03-ietf116-igp-adv-offset-01__;!!NEt6yMaO-gk!Bl7Swe9ql9VT0qGkD6FoZZzTWT2fmIx55eSncdmMgoCJetJ5-80micuqnqk79yewGB-BleOfrYpSjfI$>

    >  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://urldefense.com/v3/__https:/datatracker.ietf.org/doc/draft-ietf-lsr-isis-fast-flooding/__;!!NEt6yMaO-gk!GCoxXhuL7ryqRodFUI2f-GPQa1_Vjs9WLIB_XJtQUiKVcm6Yrxqx5p-_PmGOQFNseVacNf7mx4QUNHGf6W4I$>
    <https://datatracker.ietf.org/doc/draft-ietf-lsr-isis-fast-flooding/<https://urldefense.com/v3/__https:/datatracker.ietf.org/doc/draft-ietf-lsr-isis-fast-flooding/__;!!NEt6yMaO-gk!GCoxXhuL7ryqRodFUI2f-GPQa1_Vjs9WLIB_XJtQUiKVcm6Yrxqx5p-_PmGOQFNseVacNf7mx4QUNHGf6W4I$>>   (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<https://urldefense.com/v3/__http:/2.2.2.2/32__;!!NEt6yMaO-gk!GCoxXhuL7ryqRodFUI2f-GPQa1_Vjs9WLIB_XJtQUiKVcm6Yrxqx5p-_PmGOQFNseVacNf7mx4QUNEj8LL78$>, 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<https://urldefense.com/v3/__http:/2.2.2.2/32__;!!NEt6yMaO-gk!GCoxXhuL7ryqRodFUI2f-GPQa1_Vjs9WLIB_XJtQUiKVcm6Yrxqx5p-_PmGOQFNseVacNf7mx4QUNEj8LL78$> 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<https://urldefense.com/v3/__http:/2.2.2.2/32__;!!NEt6yMaO-gk!GCoxXhuL7ryqRodFUI2f-GPQa1_Vjs9WLIB_XJtQUiKVcm6Yrxqx5p-_PmGOQFNseVacNf7mx4QUNEj8LL78$> 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<https://urldefense.com/v3/__http:/2.2.2.2/32__;!!NEt6yMaO-gk!GCoxXhuL7ryqRodFUI2f-GPQa1_Vjs9WLIB_XJtQUiKVcm6Yrxqx5p-_PmGOQFNseVacNf7mx4QUNEj8LL78$> 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 <[e-mail]<mailto:[e-mail]> <mailto:[e-mail]<mailto:[e-mail]>>>
    On Behalf Of Acee Lindem

     > > Sent: Friday, April 7, 2023 11:43 AM

     > > To: Louis Chan <[e-mail]<mailto:[e-mail]> <mailto:[e-mail]<mailto:[e-mail]>>>

     > > Cc: lsr <[e-mail]<mailto:[e-mail]> <mailto:[e-mail]<mailto:[e-mail]>>>

     > > 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

     > > [e-mail]<mailto:[e-mail]> <mailto:[e-mail]<mailto:[e-mail]>>

     > >
    https://urldefense.com/v3/__https://www.ietf.org/mailman/listinfo/lsr_<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$

     >

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