Re: [Lsr] WG Adoption Poll for “Using IS-IS Multi-Topology (MT) for Segment Routing based Virtual Transport Network” - draft-xie-lsr-isis-sr-vtn-mt-03

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Hi Jie and all,






I'm sorry to have digressed in the adoption on this informational draft-xie-lsr-isis-sr-vtn-mt-03. However, I think these enhanced-vpn related documents are closely related, although they are divided into multiple documents. So discussing the main document (draft-dong-lsr-sr-for-enhanced-vpn) doesn't conflict with this one.





For VTN-ID, I don't believe it is interpreted by you as for scalability purpose, which is very interesting. 

Here are two things:

1) The slice-based ID is introduced into the control plane and the forwarding plane, and the SID per slice is assigned and advertised. This is done by draft-peng.

2) Optimize scalability issues. For example, the forwarding behavior of prefix-SID per slice can be inherited from flex-algo. That is clearly described by draft-bestbar.




Please don't confuse the above two things, that is, you can't say that one thing becomes another just because we try to optimize one aspect of it.


Once the slice-based ID is introduced, it can be used to distinguish which slice the service belongs to, and that is not related with whether different slice can or not share the same topology.






Regards,


PSF






原始邮件



发件人：Dongjie(Jimmy)
收件人：彭少富10053815;
抄送人：[e-mail];[e-mail];[e-mail];[e-mail];ginsberg=[e-mail];[e-mail];[e-mail];[e-mail];
日 期 ：2021年03月09日 19:32
主 题 ：Re: [Lsr] WG Adoption Poll for “Using IS-IS Multi-Topology (MT) for Segment Routing based Virtual Transport Network” - draft-xie-lsr-isis-sr-vtn-mt-03


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Hi,


 


Since this discussion is not related to the adoption poll for draft-xie-lsr-isis-sr-vtn-mt, please start a separate mail thread if you want to discuss other documents.


 


A brief reply:


 


In the current version or any previous version of draft-peng-teas-network-slicing, there is no scalability considerations, nor any mechanism to improve the scalability. While the VTN-ID in draft-dong-lsr-sr-for-enhanced-vpn was introduced for the scalability purpose one year ago. Thus I think your statement is totally wrong.


 


Best regards,


Jie


 




From: Lsr [mailto:[e-mail]] On Behalf Of [e-mail]
 Sent: Tuesday, March 9, 2021 10:52 AM
 To: Dongjie (Jimmy) <[e-mail]>
 Cc: [e-mail]; [e-mail]; [e-mail]; [e-mail]; ginsberg=[e-mail]; [e-mail]; [e-mail]; [e-mail]
 Subject: Re: [Lsr] WG Adoption Poll for “Using IS-IS Multi-Topology (MT) for Segment Routing based Virtual Transport Network” - draft-xie-lsr-isis-sr-vtn-mt-03




 

 

Hi Jie,

 

Now that you mention VTN-ID, I have to point out that the VTN-ID in draft-dong-lsr-sr-for-enhanced-vpn is actually the AII in draft-peng-teas-network-slicing, just a new name. That can be seen from the evolution of the historical versions of the these two drafts.

See https://mailarchive.ietf.org/arch/msg/spring/sgyRpAW5kzcUCdat9FtW15PPbRM/

 

I'm glad to see that the idea in draft-peng-teas-network-slicing and draft-bestbar-spring-scalable-ns have been generously adopted by you.

 

Regards,

PSF


 


原始邮件



发件人：Dongjie(Jimmy)



收件人：Tarek Saad;Gyan Mishra;Tony Przygienda;



抄送人：Les Ginsberg (ginsberg);Chongfeng Xie;Acee Lindem (acee);Robert Raszuk;[e-mail];



日 期 ：2021年03月09日 00:31



主 题 ：Re: [Lsr] WG Adoption Poll for “Using IS-IS Multi-Topology (MT) for Segment Routing based Virtual Transport Network” - draft-xie-lsr-isis-sr-vtn-mt-03




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Hi Tarek,


 


Your understanding about the scalability implication of this MT based VTN mechanism is correct, this is also described in section “scalability considerations” of this draft. The value of this mechanism is that it reuses several existing TLVs together to provide the required function.


 


As for the mechanisms which can provide better scalability, you could refer to draft-dong-lsr-sr-for-enhanced-vpn, in which a new control plane VTN-ID is introduced, and multiple VTNs can be associated with the same topology. Further discussion about that draft and its relationship with draft-bestbar-lsr-spring-sa could happen in a separate thread.


 


Best regards,


Jie


 




From: Tarek Saad [mailto:[e-mail]] 
 Sent: Monday, March 8, 2021 10:44 PM
 To: Dongjie (Jimmy) <[e-mail]>; Gyan Mishra <[e-mail]>; Tony Przygienda <[e-mail]>
 Cc: Les Ginsberg (ginsberg) <ginsberg=[e-mail]>; Chongfeng Xie <[e-mail]>; Acee Lindem (acee) <[e-mail]>; Robert Raszuk <[e-mail]>; [e-mail]
 Subject: Re: [Lsr] WG Adoption Poll for “Using IS-IS Multi-Topology (MT) for Segment Routing based Virtual Transport Network” - draft-xie-lsr-isis-sr-vtn-mt-03




 


Hi authors,


 


My understanding is the draft is proposing a separate MT topology (unique MT-ID) to identify a forwarding treatment to be enforced on a shared resource.


While this may work for limited number of MT topologies (i.e. forwarding treatments), as described in RF5120 there is overhead with creating/advertising and managing and running separate SPF for each of the MT topology. This will restrict the scalability of such approach (number of forwarding treatments to be realized) using this approach.


 


In I-D.draft-bestbar-lsr-spring-sa we are proposing carrying an independent ID (associated with the forwarding treatment) independent of the topology ID. This allows the # of forwarding treatmentst to be independent of the # of MT topologies that need to be managed by IGP; and hence, allow it to scale. Your feedback on this approach is welcome.


 


Regards,


Tarek


 


 


On 3/8/21, 9:29 AM, "Lsr on behalf of Dongjie (Jimmy)" <[e-mail] on behalf of [e-mail]> wrote:




 


Hi Gyan,


 


Thanks for your comments. 


 


As you mentioned, both MT and MI can provide separate topologies and the topology based computation, and MI can provide separate LSDBs at some additional cost (separate adjacencies, etc.). In this document, the resource of VTN mainly refers to the forwarding plane resources, thus MT is chosen as it can provide the required functionality with less overhead. 


 


Hope this helps.


 


Best regards,


Jie


 




From: Lsr [mailto:[e-mail]] On Behalf Of Gyan Mishra
 Sent: Monday, March 8, 2021 7:29 AM
 To: Tony Przygienda <[e-mail]>
 Cc: Les Ginsberg (ginsberg) <ginsberg=[e-mail]>; Chongfeng Xie <[e-mail]>; Acee Lindem (acee) <[e-mail]>; Robert Raszuk <[e-mail]>; [e-mail]
 Subject: Re: [Lsr] WG Adoption Poll for “Using IS-IS Multi-Topology (MT) for Segment Routing based Virtual Transport Network” - draft-xie-lsr-isis-sr-vtn-mt-03




 


 


Dear Authors 



 


Why was MT chosen and not MI for VTN underlay network slice underpinning.  MT instances has separate topology but not separate LSDB where MI Multi instance RFC 6822 has a separate LSDB for resources isolation and I think would be a better fit for VTN underlay provisioning.



 


MI



https://tools.ietf.org/html/rfc6822



 


Thanks 



 


Gyan



 


On Sun, Mar 7, 2021 at 10:34 AM Tony Przygienda <[e-mail]> wrote:



 


Robert ruminated: 


 


That said I think perhaps we are indeed missing LROW WG (Local Routing Operations WG) where just like in GROW WG where mainly (Global) BGP operational aspects are discussed there could be good place to discuss operational aspects of link state protocols deployment and use cases. In fact perhaps it would also free some LSR bandwidth to really focus on protocol extensions. 



 



 


+1



 


IGPs grew a zoo of horns and bells by now and no'one tells the operators which spines are poisonous ;-)






 


--- tony






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