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

["Dongjie (Jimmy)" <[e-mail]>]

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]<mailto:[e-mail]> on behalf of [e-mail]<mailto:[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]<mailto:[e-mail]>>
Cc: Les Ginsberg (ginsberg) <ginsberg=[e-mail]<mailto:ginsberg=[e-mail]>>; Chongfeng Xie <[e-mail]<mailto:[e-mail]>>; Acee Lindem (acee) <[e-mail]<mailto:[e-mail]>>; Robert Raszuk <[e-mail]<mailto:[e-mail]>>; [e-mail]<mailto:[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]<mailto:[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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Gyan Mishra

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