[Cake] Re: help request for cake on a large network

[David Lang <david@lang.hm>]

Jonathan Morton wrote:

> On Sunday, 28 September 2025, David Lang wrote:
>> I'm starting to prepare for the next Scale conference and we are switching from
>> Juniper routers to Linux routers. This gives me the ability to implement cake.
>>
>> One problem we have is classes that tell everyone 'go download this' that
>> trigger hundreds of people to hammer the network at the same time (this is both
>> a wifi and a network bandwidth issue, wifi is being worked on)
>>
>> The network is pretty flat, a couple of subnets each on ipv4 and ipv6.
>>
>> Any suggestions on how to configure cake for this sort of environment where
>> there are so many devices?
>
> So far as Cake is concerned, the normal setup should work fine even under 
> stress conditions.  If there are too many simultaneous flows to achieve full 
> flow isolation, it degrades gracefully to statistical multiplexing, and you 
> still have the AQM working to keep everything responsive.  Or rather, a 
> thousand AQMs working in parallel...

what would need to be done to increase resources to allow for full isolation of 
more flows?

> Of course, this only matters when Cake is set up to be the bottleneck.  If 
> wifi is the bottleneck, you'll want a wifi stack with integrated fq_codel, 
> which I believe still applies to only some hardware since it needs to manage 
> the MAC queue which some devices don't expose.  This has the extra smarts 
> needed to adapt gracefully to wifi's foibles, and might already be enough to 
> convert an effectively nonfunctional wifi into one that feels, if not fast, 
> then at least reliable.

I am doing everything I can to eliminate wifi as the bottleneck and overload our 
uplink ;-p

mostly the wifi bottleneck is being eliminated by having lots of separate APs 
for people to connect to.

David Lang