Re: Vyatta as a BRAS

[Matthew Kaufman <matthew () matthew at>]

Joe Greco wrote:
> This isn't a new issue.  Quite frankly, software routers have some very
> great strengths, and also some large weaknesses.
>
> Advocates of hardware based solutions frequently gloss over their own
> weaknesses.
>
> Let's talk plainly here.
>
> I'm not going to touch on things like Cisco's software-powered systems,
> and for purposes of this discussion, let's take "hardware" to mean
> "hardware-accelerated" solutions that implement forwarding in silicon.
> That makes a fairly clear delineation between something like a Cisco
> 7600 and a Vyatta router.  So.
>
> Hardware router: Insanely great forwarding rates.
> Software router: Varies substantially based on platform architecture and
>         software competence.  Generally speaking, a competent config can
>         run 1Gbps ports without issue, but >=10Gbps gets dicey. ... [remaining good summary removed]
>   

There's really three categories:
1) Devices which make all forwarding decisions and do the forwarding in 
software
2A) Devices which do forwarding in hardware, but which have a 
significantly limited forwarding table and punt to software for misses
2B) Devices which do forwarding in hardware, and which have hardware 
forwarding tables sufficient to hold your whole routing table

These then have the following attributes:
1) Can't handle traffic forwarding rates as high as the others, can do 
complex filtering, often least expensive choice, may scale well with 
commodity hardware scaling (processor, RAM, interface speeds). Great 
choice if you operate within their limitations and/or need their 
flexibility and potential processing complexity.
2A) Can handle higher forwarding rates, often can forward packets using 
less power-per-bps than systems in category 1, filtering at these rates 
is limited in capability, tends to scale with improvements in LAN 
switching technology (these are essentially layer 3 switches). Great in 
data centers, network edges. Dangerous in places where forwarding table 
exceeds hardware cache limits. (See Code Red worm stories)
2B) Can handle high forwarding rates, potentially lowest power-per-bps 
for forwarding if you are operating at sufficient scale, filtering at 
these rates is limited in capability, scales with investment in these 
highly specialized devices and the underlying TCAM technology. Great for 
Internet backbone network routing if you have the money. Expensive.



Matthew Kaufman