[Idr] Re: Fwd: I-D Action: draft-wang-idr-dpf-00.txt

[Robert Raszuk <[e-mail]>]

Dear Kevin,

I know very well what RFC 7938 says. In fact I did review this document
well before it became an RFC :)

But what happened next is that while RFC7938 make a valid observation on
how one can build MSDCs lots of folks misinterpreted it as the only guide
on how to build even a few racks of DC fabrics.

So yes, using BGP to construct dynamic routing in the DC fabrics has its
use cases that are really applicable to only a handful of deployments. And
I am not aware that any of the MSDCs would be asking you for logical
transport planes within their fabrics.

All other DCs would be much better off using IGP for underlay and BGP for
overlay as a design pattern.

When I constructed 10 full racks of hardware using ISIS folks were shocked
- and pointed out that I am not using an IETF standard approach :). Then
when I demonstrated that connectivity restoration upon any node or link
failure is repaired in less then 50 ms the masks went off.

Maybe what is actually needed is an  informational RFC - just like RFC7938
- simply illustrating that one can construct DC using ISIS. It is obvious
to me, but I admit there is no RFC I am aware of to show operators that
"Large-Scale Data Centers" can be robustly build with IGPs.

Kind regards,
Robert


On Tue, Dec 2, 2025 at 7:24 PM Wang, Kevin <[e-mail]> wrote:

> Hi Robert and Gyan,
>
> Thanks for your feedback! Your observation is correct that IGP Flex Algo
> could achieve the same. BGP DPF can be though as a BGP counterpart of IGP
> Flex Algo to some extent (though not precisely).
>
> As explained in the “Introduction” section of this draft, BGP DPF is
> designed for the current IP fabric environment where EBGP is usually the
> only protocol used for routing. Section 5 of RFC 7938 explains why DC
> fabrics use EBGP as the sole routing protocol.
>
> Thanks,
> Kevin
>
> *From: *Gyan Mishra <[e-mail]>
> *Date: *Tuesday, December 2, 2025 at 7:43 AM
> *To: *Robert Raszuk <[e-mail]>
> *Cc: *idr@ietf. org <[e-mail]>, lsr <[e-mail]>
> *Subject: *[Idr] Re: Fwd: I-D Action: draft-wang-idr-dpf-00.txt
>
> I agree with Robert that you could use RFC 9502 IGP Flex Algo in IP
> networks to build disjoint planes as desired.
>
> You could also use SRv6 with IGP Flex Algo with SR RFC 9350 which uses
> IPv6 data plane and build your disjoint planes.
>
> Thanks
>
> Gyan
>
> On Tue, Dec 2, 2025 at 6:32 AM Robert Raszuk <[e-mail]> wrote:
>
> Hi,
>
> In respect to the subject draft ... why would you not use IGP Flexible
> Algorithm for it ?
>
> Are you going to port now years of work from IGP to BGP to achieve the
> same ?
>
> Besides, in a non-blocking fabric latency is really not a factor. So you
> want to logically partition it to make it blocking them worry about what
> travels on which such logical plane ? Is this a reasonable direction ?
>
> Thx,
> R.
>
> ---------- Forwarded message ---------
> From: <[e-mail]>
> Date: Mon, Dec 1, 2025 at 10:49 PM
> Subject: I-D Action: draft-wang-idr-dpf-00.txt
> To: <[e-mail]>
>
>
> Internet-Draft draft-wang-idr-dpf-00.txt is now available.
>
>    Title:   BGP Deterministic Path Forwarding (DPF)
>    Authors: Kevin Wang
>             Michal Styszynski
>             Wen Lin
>             Mahesh Subramaniam
>             Thomas Kampa
>             Diptanshu Singh
>    Name:    draft-wang-idr-dpf-00.txt
>    Pages:   18
>    Dates:   2025-12-01
>
> Abstract:
>
>    Modern data center (DC) fabrics typically employ Clos topologies with
>    External BGP (EBGP) for plain IPv4/IPv6 routing.  While hop-by-hop
>    EBGP routing is simple and scalable, it provides only a single best-
>    effort forwarding service for all types of traffic.  This single
>    best-effort service might be insufficient for increasingly diverse
>    traffic requirements in modern DC environments.  For example, loss
>    and latency sensitive AI/ML flows may demand stronger Service Level
>    Agreements (SLA) than general purpose traffic.  Duplication schemes
>    which are standardized through protocols such as Parallel Redundancy
>    Protocol (PRP) require disjoint forwarding paths to avoid single
>    points of failure.  Congestion avoidance may require more
>    deterministic forwarding behavior.
>
>    This document introduces BGP Deterministic Path Forwarding (DPF), a
>    mechanism that partitions the physical fabric into multiple logical
>    fabrics.  Flows can be mapped to different logical fabrics based on
>    their specific requirements, enabling deterministic forwarding
>    behavior within the data center.
>
> The IETF datatracker status page for this Internet-Draft is:
> https://datatracker.ietf.org/doc/draft-wang-idr-dpf/
> <https://urldefense.com/v3/__https://datatracker.ietf.org/doc/draft-wang-idr-dpf/__;!!NEt6yMaO-gk!EP_lEYmqbOUApQqqOz-ZuP9CsojS2gbvLvgQfxoYTXPXtS-0yjfv8ElqZwJBCRfOLFY6nymWoR5eJlshPeG9$>
>
> There is also an HTML version available at:
> https://www.ietf.org/archive/id/draft-wang-idr-dpf-00.html
> <https://urldefense.com/v3/__https://www.ietf.org/archive/id/draft-wang-idr-dpf-00.html__;!!NEt6yMaO-gk!EP_lEYmqbOUApQqqOz-ZuP9CsojS2gbvLvgQfxoYTXPXtS-0yjfv8ElqZwJBCRfOLFY6nymWoR5eJjgsy_TY$>
>
> Internet-Drafts are also available by rsync at:
> rsync.ietf.org::internet-drafts
>
>
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