few big monolithic PEs vs many small PEs

adamv0025 at netconsultings.com adamv0025 at netconsultings.com
Fri Jun 21 08:32:56 UTC 2019


Hey Mark,
> From: Mark Tinka
> Sent: Thursday, June 20, 2019 3:27 PM
> 
> On 19/Jun/19 22:22, adamv0025 at netconsultings.com wrote:
> 
> > Yes it will cost a bit more (router is more expensive than a LC)
> 
> I found the reverse to be true... chassis' are cheap. Line cards are costly.
> 
Well yes but if say I compare just a single line-card cost to a standalone fixed-format 1RU router with a similar capacity -the card will always be cheaper and then as I'll start adding cards on the left-hand side of the equation things should start to even out gradually (problem is this gradual increase is just a theoretical exercise -there are no fixed PE products to do this with).
Yes I can compare mpc7 with a mx204. Or asr9901 with some tomahawk card(s) probably not apples to apples? 
But if I would venture above 1/2RU then I'm back in chassis based systems paying extra for REs/RPs and fabric and fans and PSUs... with every small PE I'm putting in so then I'm talking about add two new cards to existing chassis or ad two new cards to a new chassis. 

Also one interesting CAPEX factor to consider is the connectivity back to the core, as with many small PEs in a POP one would need a lot of ports on core routers and also once again the aggregation factor is somewhat lost in doing so. Where I'd have just a couple of PEs with 100G back to the core now I'd need bunch of 10s-bundled or 40s -would probably need additional cards in core routers to accommodate the need for PE ports in the POP.       

> 
> >
> > Would like to hear what are your thoughts on this conundrum.
> 
> So this depends on where you want to deliver your service, and the function,
> in my opinion.
> 
> If you are talking about an IP/MPLS-enabled Metro-E network, then having
> several, smaller routers spread across one or more rings is cheaper and more
> effective.
> 
Well playing devil's advocate, having the metro rings build as dumb L1 or L2 with pair of PEs at the top is cheaper -although not much cheaper nowadays the economics in this sector changed significantly over the past years. 


> If you are delivering services to large customers from within a data centre,
> large edge routers make more sense, particularly given the rising costs of co-
> location.
> 
So this particular case, the major POPs, is actually where we ran into the problem of RE/RP becoming full (too many VRFs/Routes/BGP sessions) halfway through the chassis.
Hence I'm considering whether it's actually better to go with multiple small chassis and/or fixed form PEs in the rack as opposed to half/full rack chassis. 
 

adam





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