Re: Cost per prefix [was: request for help w/ ATT and terminology]

["William Herrin" <herrin-nanog () dirtside com>]

On Jan 20, 2008 1:11 PM, Patrick W. Gilmore <patrick () ianai net> wrote:
> On Jan 20, 2008, at 12:22 PM, William Herrin wrote:
> > > I think you mean in tiny fractions of a single cent per router per
> > > year
> >
> > No, I don't. The lower bound for that particular portion of the cost
> > analysis is easy to calculate:
> > ( [entry level router's cost attributable to prefixes]/[expected
> > lifespan] ) / [DFZ prefix count]
>
> Your calculation is in error.

Patrick,

Feel free to correct it. Substitute any numbers that you can
*justify*, add any factors that you can justify and recalculate. If
your justification is sensible, I'll adjust my own numbers
accordingly. I'd prefer that the numbers be lower so I can find a way
to justify IPv6 PI space. :)

However, please try not to disagree merely because you don't want to
accept the results. Denial is not productive.


> > Entry level DFZ router: $40,000
> > Stacked 1U layer-3 switches with similar switching capacity and port
> > density: $10,000
>
> One of us is very confused.  Given that I order "entry level DFZ
> routers" all the time far less than $40K every month, I am going to
> guess it is not me.

Perhaps your definition of "entry level DFZ router" differs from mine.
I selected a Cisco 7600 w/ sup720-3bxl or rsp720-3xcl as my baseline
for an entry level DFZ router. This seemed to be the minimum Cisco kit
which could reasonably be expected to remain in service as a full
table DFZ router through 1/2011. What would you select instead?

Please note that neither a Cisco 7200 nor a sup/rsp720 prior to the
3bxl/3cxl can be reasonably expected to have 3-year lifespan in the
DFZ. They simply can't keep up with the expected growth in the routing
table.

I'll confess to not knowing the Juniper line well enough to comment on
their equivalent system. Do they cost radically less than Cisco gear?


> The difference is much, much, much greater than that.  Can the switch
> do ACLs?  Policy routing?  SFlow with the same sampling rate?  Same
> number of BGP session?

Is there some alternate piece of cheap hardware that supports the DFZ
prefix count at high data rates but doesn't have those features? If
the answer is no (and I'm pretty sure the answer is no), then the
prefix count remains the proper attribution for the cost delta.

And yes, today's "virtual chassis" 1U switch stacks are pretty slick.
I can't speak to sflow or policy routing but many if not most support
both BGP and ACLs. Most also have 128M on the control plane and 8k or
16k entries in the TCAMs which obviously does not support a DFZ table.

Regards,
Bill Herrin


-- 
William D. Herrin                  herrin () dirtside com  bill () herrin us
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