Re: [Lsr] IETF-116 LSR - IGP extensions for Advertising Offset forFlex-Algorithm

[Gyan Mishra <[e-mail]>]

Hi Krzysztof

After reading the draft and mailing list review of the draft, the main
motivation of this draft is for IETF Network slicing end to end and having
more granularity with a flex algo by introducing virtual Flex Algo concept.


Good work by the authors.

Thanks

Gyan

On Thu, May 11, 2023 at 11:17 PM Dongjie (Jimmy) <jie.dong=
[e-mail]> wrote:

> Hi Krzysztof,
>
>
>
> It is good that we are converging on the benefit of sharing of Flex-Algo
> based calculation among multiple virtual networks (NRPs).  And this part
> can be independent from the optimization of SID advertisement in the
> LSPs/LSAs.
>
>
>
> If we further consider the SID advertisement optimization, my
> understanding is the reduction in control message overhead would be
> transferred to the complexity in the label/address planning of the network,
> and without proper design it may result in waste of the MPLS labels or IP
> addresses. Thus some trade-off between the message size and the
> label/address planning and utilization would need to be considered.
>
>
>
> Best regards,
>
> Jie
>
>
>
> *From:* Krzysztof Szarkowicz [mailto:[e-mail]]
> *Sent:* Wednesday, May 10, 2023 3:53 AM
> *To:* Dongjie (Jimmy) <[e-mail]>
> *Cc:* linchangwang <[e-mail]>; Acee Lindem <
> [e-mail]>; Peter Psenak <[e-mail]>; 程伟强 <
> [e-mail]>; Louis Chan <[e-mail]>; Les
> Ginsberg (ginsbe <[e-mail]>; lsr <[e-mail]>; Robert Raszuk <
> [e-mail]>
> *Subject:* Re: [Lsr] IETF-116 LSR - IGP extensions for Advertising Offset
> forFlex-Algorithm
>
>
>
> Hi Jie,
>
>
>
> Agreed, draft-dong-lsr-sr-enhanced-vpn and draft-chan-lsr-igp-adv-offset
> use different approach for advertising multiple data-plane identifiers for
> single Flex-Algo.  However, the methodology is only somewhat similar to the
> methodology of SRv6 optimization in draft-dong. In draft-dong it
> is advertised one-by-one (second Figure in Section 5.2.1), whereas
> in draft-chan-lsr-igp-adv-offset it is bulk adertisement.
>
>
>
> So, where there are some similarities, there are as well differences.
>
>
>
> Best regards,
>
> Krzysztof
>
>
>
>
>
> On 2023 -May-09, at 14:33, Dongjie (Jimmy) <[e-mail]> wrote:
>
>
>
>
>
> *[External Email. Be cautious of content]*
>
>
>
>
>
> Hi Krzysztof,
>
>
>
> As I commented during the presentation and in the mail below, the
> mechanism of sharing the SPF of one Flex-Algo among multiple NRPs was
> already documented in
> https://datatracker.ietf.org/doc/html/draft-dong-lsr-sr-enhanced-vpn-08
> <https://urldefense.com/v3/__https:/datatracker.ietf.org/doc/html/draft-dong-lsr-sr-enhanced-vpn-08__;!!NEt6yMaO-gk!AJqIpg0GT7A87f6OpfCXNApwKFr53KnkTxdR0c8z_-7A2EUJalQJaqQJx_hSrDDeKPFJIbMFSZJqSwKhUg3j$>
> .
>
>
>
> As for the data plane distinguisher, both per-NRP SR SIDs (i.e. using the
> top label as you mentioned for SR-MPLS) and the dedicated NRP IDs can be
> used with that mechanism. That document also proposes some optimizations
> for the advertisement of per-NRP SRv6 Locators and SIDs.
>
>
>
> Then my understanding of draft-chan-lsr-igp-adv-offset is that it proposes
> some optimization for Per-NRP SR-MPLS SIDs to advertise label blocks
> instead of specific SIDs. The methodology is similar to the SRv6
> optimization in draft-dong, while as others pointed out, from the label
> manageability perspective it may be difficult.
>
>
>
> Best regards,
>
> Jie
>
>
>
> *From:* Krzysztof Szarkowicz [mailto:[e-mail]
> <[e-mail]>]
> *Sent:* Tuesday, May 2, 2023 7:32 PM
> *To:* Dongjie (Jimmy) <[e-mail]>
> *Cc:* linchangwang <[e-mail]>; Acee Lindem <
> [e-mail]>; Peter Psenak <[e-mail]>; 程伟强 <
> [e-mail]>; Louis Chan <[e-mail]>; Les
> Ginsberg (ginsbe <[e-mail]>; lsr <[e-mail]>; Robert Raszuk <
> [e-mail]>
> *Subject:* Re: [Lsr] IETF-116 LSR - IGP extensions for Advertising Offset
> forFlex-Algorithm
>
>
>
> Hi Jie,
>
>
>
> You are right that "Virtual Flex-Algos” (or, whatever term is / will be
> used for it) is to share the SPF (and, in essence, share the path), but to
> distinguish data plane behavior (for example, to have multiple bandwidth
> profiles within single Flex-Algo, on selected nodes ob the
> path). draft-chan-lsr-igp-adv-offset main goal is to keep simple data plane
> (e.g., top label is used as the distinguisher to enforce different behavior
> on selected nodes on the path), while mapping to NRPs requires data plane
> change.
>
>
>
> And yes, all solutions have some benefits or drawbacks. NRP benefit os
> scalability, and cost of complexity (data plane change). The proposal
> in draft-chan-lsr-igp-adv-offset is less scalable, but sufficient for many
> uses uses, and is simple (no data plane change).
>
>
>
>
> Thanks,
>
> Krzysztof
>
>
>
>
>
>
>
> On 2023 -Apr-13, at 14:06, Robert Raszuk <[e-mail]> wrote:
>
>
>
>
>
> *[External Email. Be cautious of content]*
>
>
>
>
>
> Jie,
>
>
>
> Your Enhanced VPN documents are very well written - thx for sharing
> the pointer to them. However I don't think I would put NRP as a new
> Extension Header for IPv6 data plane or Post Stack Data for MPLS data plane
> to indicate PHB in the packets.
>
>
>
> I think there are better alternatives which do not require hardware
> extensions or modification.
>
>
>
> Thx,
>
> Robert.
>
>
>
>
>
> On Thu, Apr 13, 2023 at 1:24 PM Dongjie (Jimmy) <jie.dong=
> [e-mail]> wrote:
>
> Hi Krzysztof,
>
>
>
> If my understanding is correct, you and Louis are considering about two
> separate optimizations:
>
>
>
> 1.      Allowing multiple “Virtual Flex-Algos” to share the SPF
> calculation of one “legacy” Flex-Algo.
>
>
>
> This can be addressed by the mechanisms described in section 2 of
> https://datatracker.ietf.org/doc/html/draft-dong-lsr-sr-enhanced-vpn-08
> <https://urldefense.com/v3/__https:/datatracker.ietf.org/doc/html/draft-dong-lsr-sr-enhanced-vpn-08__;!!NEt6yMaO-gk!AJqIpg0GT7A87f6OpfCXNApwKFr53KnkTxdR0c8z_-7A2EUJalQJaqQJx_hSrDDeKPFJIbMFSZJqSwKhUg3j$>
> .
>
>
>
> More specifically, that document allows multiple NRPs to associate with
> the same Flex-Algo, so that the Flex-Algo computation could be reused. NRP
> is used to represent different set of network resources, and Flex-Algo is
> still used to specify the topology and computation constraints for the NRP.
> In that way, no change to Flex-Algo is needed.
>
>
>
> 2.      Reducing the amount of SR SIDs which are used to indicate
> different set of bandwidth reservation.
>
>
>
> The approach of using SR SIDs to represent different set of network
> resources is suitable for networks in which the number of NRPs are
> relatively small. As the number of NRPs increases, there will be
> scalability challenge not only in the control plane but also in the data
> plane. In that case, a more scalable and IGP friendly approach is to
> introduce a network-wide NRP ID into the packet. This is also described in
> section 5.3 of draft-dong-lsr-sr-enhanced-vpn-08.
>
>
>
> Hope this helps.
>
>
>
> Best regards,
>
> Jie
>
>
>
> *From:* Lsr <[e-mail]> *On Behalf Of *Krzysztof Szarkowicz
> *Sent:* Wednesday, April 12, 2023 11:42 PM
> *To:* Robert Raszuk <[e-mail]>
> *Cc:* linchangwang <[e-mail]>; Acee Lindem <
> [e-mail]>; Peter Psenak <[e-mail]>; 程伟强 <
> [e-mail]>; Louis Chan <[e-mail]>; Les
> Ginsberg (ginsbe <[e-mail]>; lsr <[e-mail]>
> *Subject:* Re: [Lsr] IETF-116 LSR - IGP extensions for Advertising Offset
> forFlex-Algorithm
>
>
>
> 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]> 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 4:52 PM linchangwang <[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]]
> *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]> 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]] 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]>
>     *收件
>     人：*"Les Ginsberg (ginsberg)" <[e-mail]>,Acee Lindem <
> [e-mail]>
>     *抄 送:
>     *lsr  <[e-mail]>,Krzysztof Szarkowicz  <[e-mail]>,Weiqiang
> Cheng  <[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]>
>     *Sent:* Tuesday, April 11, 2023 11:03 PM
>     *To:* Louis Chan <[e-mail]>; Acee Lindem <
> [e-mail]>
>     *Cc:* lsr <[e-mail]>; Krzysztof Szarkowicz
>     <[e-mail]>; Weiqiang Cheng
>     <[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]>>
>
>      > Sent: Monday, April 10, 2023 11:01 PM
>
>      > To: Les Ginsberg (ginsberg) <[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
>
>      >
>
>      > Hi Les,
>
>      >
>
>      > Thanks for your questions. Please see inline [lc] below.
>
>      >
>
>      > /Louis
>
>      >
>
>      > -----Original Message-----
>
>      > From: Les Ginsberg (ginsberg) <[e-mail]
>     <mailto:[e-mail]>>
>
>      > Sent: Saturday, April 8, 2023 7:34 AM
>
>      > To: Acee Lindem <[e-mail]
>     <mailto:[e-mail]>>; Louis Chan <[e-mail]
>     <mailto:[e-mail]>>
>
>      > Cc: lsr <[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]>>
>     On Behalf Of Acee Lindem
>
>      > > Sent: Friday, April 7, 2023 11:43 AM
>
>      > > To: Louis Chan <[e-mail] <mailto:[e-mail]>>
>
>      > > Cc: lsr <[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]>
>
>      > >
>     https://urldefense.com/v3/__https://www.ietf.org/mailman/listinfo/lsr_
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>
>      > > EoixpkxsfMnbqwbR0bpHgoS9E$
>
>      >
>
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>
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