[AusNOG] Cisco routers on NBN 100/40Mbps connection

[Reuben Farrelly]

On 10/08/2014 10:53 AM, James Jazza wrote:
> Hi Guys,
>
> We are hearing reports that Cisco 881 routers are not suitable for NBN
> 100/40Mbps connections, and that we need to use the next model up - a
> Cisco 1841 instead.

The 1841s are approaching end of life.  You will want to look at a 1921 
or 1941 for this or even higher, depending on what features you want to 
enable.  Not only because of the throughput increase that you'll need, 
but it doesn't make much sense to deploy 10 year old hardware on a new 
link..

> Can anyone comment on this? As the Cisco 881 has 100Mbps internal ports,
> so I would have thought it would be ok.

A 100M port line rate does not indicate, or even suggest, 100M of 
routing throughput.

Generally speaking on a L2/L3 switching platform you will get line rate 
between switched ports, as the switching is done in hardware.

But on a router where you're doing routing on a software based platform 
where the CPU is heavily involved in packet forwarding, the forwarding 
numbers are almost always much much lower than port line rate.

The 881/1800/1900/2900/3900s are for the most part software based 
routers where the limiting factor in terms of throughput is the CPU 
speed and utilisation.

This document is very out of date (last update November 2009) but it's a 
good relative comparison between platforms, as to what you may be able 
to get:

http://www.cisco.com/web/partners/downloads/765/tools/quickreference/routerperformance.pdf

Reuben