few big monolithic PEs vs many small PEs

Thu Jun 27 11:47:11 UTC 2019

> From: James Bensley <jwbensley at gmail.com>
> Sent: Thursday, June 27, 2019 9:56 AM
> 
> One experience I have made is that when there is an outage on a large PE,
> even when it still has spare capacity, is that the business impact can be too
> much to handle (the support desk is overwhelmed, customers become irate
> if you can't quickly tell them what all the impacted services are, when service
> will be restored, the NMS has so many alarms it’s not clear what the problem
> is or where it's coming from etc.).
> 
I see what you mean, my hope is to address these challenges by having a "single source of truth" provisioning system that will have, among other things, also HW-customer/service mapping -so Ops team will be able to say that if particular LC X fails then customers/services X,Y,Z will be affected. 
But yes I agree with smaller PEs any failure fallout is minimized proportionally.
 
> 
> This doesn’t mean there isn’t a place for large routers. For example, in a
> typical network, by the time we get to the P nodes layer in the core we tend
> to have high levels of redundancy, i.e. any PE is dual-homed to two or more P
> nodes and will have 100% redundant capacity. 
Exactly, while the service edge topology might be dynamic as a result of horizontal scaling the core on the other hand I'd say should be fairly static and scaled vertically, that is I wouldn't want to scale core routers horizontally and as a result have core topology changing with every P scale out iteration at any POP, that would be bad news for capacity planning and traffic engineering... 

> 
> I’ve tried to write some of my experiences here
> (https://null.53bits.co.uk/index.php?page=few-larger-routers-vs.-many-
> smaller-routers).
> The tl;dr version though is that there’s rarely a technical restriction to having
> fewer large routers and it’s an operational/business impact problem.
> 
I'll give it a read, cheers.

adam