Re: Distributed Router Fabrics

[Tom Beecher <beecher () beecher cc>]

Much of this is right, but again with caveats.

- The boxes are fungible, to a point. Differences in ASICs, buffers, etc
can really create traffic problems if you mix wrong.  You don't want to be
yolo'ing whatever is cheap this month in there.
- You're going to eventually have a feature need that commercial management
software doesn't account for. Can they build it for you, and how much is
that? If you built your own software to manage it, how much does it cost
you to build it?
- You're very correct about how initial mistakes or things you didn't know
can bite you hard later. The wrong growing pain can really hurt if you're
not prepared for it.
- Really have to think about the internals and the design. There are some
companies who have presented on how they built these things, and when you
listen to their protocol design, it makes your head hurt how much
overcomplication was built in.

Like I said before, distributed fabrics CAN be amazing, but there are
always tradeoffs. There are some things you don't have to care about with a
big chassis, but you do with a DF. And the other way around as well. It's
about picking which set of things you WANT to deal with, or are better for
you to deal with than the other.

On Tue, Dec 24, 2024 at 9:50 AM David Sinn <dsinn () uw edu> wrote:

> From experience I can tell you that once you fully operationalize the
> pizza box model you will never go back to the chassis model. Why would you
> trade, open, standards based model for interconnect (OSPF and BGP work
> great at scale) for proprietary black boxes that do stupid router tricks to
> make a bunch of discrete components pretend to be one along with giving you
> the benefit of a huge blast-radius when the software inevitably breaks?
> Distributed ARP/ND, solved. Actually distributed BFD (not "it's all running
> on one line card because customers like LACP bundles spread between line
> cards and that's really hard to distribute reliably), solved. Pizza box
> models means the boxes are fungible. So you can competitively bid between
> multiple suppliers and pick and choose who you want to buy from depending
> on what is the most important thing at the time (delivery dates? price?
> which of them is annoying you the least at that moment in time?). They are
> also infinitely more scaleable(*) than any big chassis model. State of the
> art 5 years ago had Internet edge systems deploying with 8k of 400G ports
> and datacenter deployments with 65k 400G ports using the same fundamental
> design.
>
> The real downside: vendors don't like the flexibility that it affords the
> customer and the meaninglessness of differentiation between vendors that it
> drives the operators to avoid.
>
> David
>
> (*) - Among some of the critical things to get right from the outset is
> what peak scale you want to have for the fabric because recabling is not
> something to be taken lightly...
>
>
> On Dec 23, 2024, at 7:15 AM, Mike Hammett <nanog () ics-il net> wrote:
>
> "Obviously, at some point, buying a big chassis..."
>
> Actually, as I read more about it and watch more videos about it, it seems
> like that isn't necessarily true. The claims they have at the top end
> surpass what any chassis platform I've seen is capable of, though I don't
> know that they actually have pushed the upper bounds of what's possible in
> the real world.
>
>
>
> -----
> Mike Hammett
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> ------------------------------
> *From: *"Mike Hammett" <nanog () ics-il net>
> *To: *"NANOG" <nanog () nanog org>
> *Sent: *Friday, December 20, 2024 10:06:36 AM
> *Subject: *Distributed Router Fabrics
>
> I've noticed that the whitebox hardware vendors are pushing distributed
> router fabrics, where you can keep buying pizza boxes and hooking them into
> a larger and larger fabric. Obviously, at some point, buying a big chassis
> makes more sense. Does it make sense building up to that point? What are
> your thoughts on that direction?
>
>
>
> -----
> Mike Hammett
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