Re: Distributed Router Fabrics

[Mike Hammett <nanog () ics-il net>]

"Differences in ASICs, buffers, etc can really create traffic problems if you mix wrong" 


This is why I liked to create this thread. In the information I've read so far, the marketing speak was more or less 
that it worked and to just move on. It's good to learn that there are caveats that need to be explored. 




"makes your head hurt how much overcomplication" 


Aren't there memes about Silicon Valley re-inventing things we already have in a more complicated and cumbersome way? 




----- 
Mike Hammett 
Intelligent Computing Solutions 

Midwest Internet Exchange 

The Brothers WISP 

----- Original Message -----

From: "Tom Beecher" <beecher () beecher cc> 
To: "David Sinn" <dsinn () uw edu> 
Cc: "Mike Hammett" <nanog () ics-il net>, "NANOG" <nanog () nanog org> 
Sent: Tuesday, December 24, 2024 9:12:17 AM 
Subject: Re: Distributed Router Fabrics 


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... 





<blockquote>

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 
Intelligent Computing Solutions 

Midwest Internet Exchange 

The Brothers WISP 



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 
[ http://www.ics-il.com/ | Intelligent Computing Solutions ] 
[ https://www.facebook.com/ICSIL ] [ https://plus.google.com/+IntelligentComputingSolutionsDeKalb ] [ 
https://www.linkedin.com/company/intelligent-computing-solutions ] [ https://twitter.com/ICSIL ] 
[ http://www.midwest-ix.com/ | Midwest Internet Exchange ] 
[ https://www.facebook.com/mdwestix ] [ https://www.linkedin.com/company/midwest-internet-exchange ] [ 
https://twitter.com/mdwestix ] 
[ http://www.thebrotherswisp.com/ | The Brothers WISP ] 
[ https://www.facebook.com/thebrotherswisp ] [ https://www.youtube.com/channel/UCXSdfxQv7SpoRQYNyLwntZg ] 



</blockquote>