/27 the new /24

Mike Hammett nanog at ics-il.net
Fri Oct 2 18:37:54 UTC 2015

Chances are the revenue passing scales to some degree as well. Small business with small bandwidth needs buys small and has small revenue. Big business with big bandwidth needs buys big and has big revenue to support big router. 

I can think of no reason why ten years goes by and you haven't had a need to throw out the old network for new. If your business hasn't scaled with the times, then you need to get rid of your Cat 6500 and get something more power, space, heat, etc. efficient. 

I saw someone replace a stack of Mikrotik CCRs with a pair of old Cisco routers. I don't know what they were at the moment, but they had GBICs, so they weren't exactly new. Each router had two 2500w power supplies. They'll be worse in every way (other than *possibly* BGP convergence). The old setup consumed at most 300 watts. The new setup requires $500/month in power... and is worse. 

Stop using old shit. 

Mike Hammett 
Intelligent Computing Solutions 

Midwest Internet Exchange 

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

From: "William Herrin" <bill at herrin.us> 
To: "Mike Hammett" <nanog at ics-il.net> 
Cc: "NANOG" <nanog at nanog.org> 
Sent: Friday, October 2, 2015 1:09:16 PM 
Subject: Re: /27 the new /24 

On Fri, Oct 2, 2015 at 11:50 AM, Mike Hammett <nanog at ics-il.net> wrote: 
> How many routers out there have this limitation? A $100 router 
> I bought ten years ago could manage many full tables. If 
> someone's network can't match that today, should I really have 
> any pity for them? 

Hi Mike, 

The technology doesn't work the way you think it does. Or more 
precisely, it only works the way you think it does on small (cheap) 
end-user routers. Those routers do everything in software on a 
general-purpose CPU using radix tries for the forwarding table (FIB). 
They don't have to (and can't) handle both high data rates and large 
routing tables at the same time. 

For a better understanding how the big iron works, check out 
https://www.pagiamtzis.com/cam/camintro/ . You'll occasionally see 
folks here talk about TCAM. This stands for Ternary Content 
Addressable Memory. It's a special circuit, different from DRAM and 
SRAM, used by most (but not all) big iron routers. The TCAM permits an 
O(1) route lookup instead of an O(log n) lookup. The architectural 
differences which balloon from there move the router cost from your 
$100 router into the hundreds of thousands of dollars. 

Your BGP advertisement doesn't just have to be carried on your $100 
router. It also has to be carried on the half-million-dollar routers. 
That makes it expensive. 

Though out of date, this paper should help you better understand the 
systemic cost of a BGP route advertisement: 

Bill Herrin 

William Herrin ................ herrin at dirtside.com bill at herrin.us 
Owner, Dirtside Systems ......... Web: <http://www.dirtside.com/> 

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