[101936] in North American Network Operators' Group
Re: Cost per prefix [was: request for help w/ ATT and terminology]
daemon@ATHENA.MIT.EDU (Patrick W. Gilmore)
Sun Jan 20 22:19:45 2008
Cc: "Patrick W. Gilmore" <patrick@ianai.net>
From: "Patrick W. Gilmore" <patrick@ianai.net>
To: nanog@merit.edu
In-Reply-To: <3c3e3fca0801201746j472e0033pfd08ca2724456ccb@mail.gmail.com>
Date: Sun, 20 Jan 2008 21:46:40 -0500
Errors-To: owner-nanog@merit.edu
On Jan 20, 2008, at 8:46 PM, William Herrin wrote:
> So at this point, the part of my analysis you still dispute is where I
> claimed that 75% of the $40k cost of an entry-level DFZ router was
> attributable to its ability to carry the needed prefix count.
>
> I didn't ask you to justify what you thought made my assessment of the
> attributable cost was wrong, although I'm glad you agree that you
> haven't done so. You also haven't adequately explained why the
> justification I used to arrive at those numbers is in error.
As I said before, your calculation is in error. I very clearly
explained why, but you threw out my explanation below. Apparently I
assumed you had knowledge you did not. Please forgive me for not
assuming you were ignorant. I shall not repeat my mistake.
> For example, the Cisco 3750G has all of features except for the
> ability to hold 300k+ prefixes. Per CDW, the 48-port version costs
> $10k, so the difference (ergo cost attributable to prefix count) is
> $40k-$10k=$30k, or 75%.
Unfortunately, I have to run real packets through a real router in the
real world, not design a network off CDW's website.
As a simple for-instance, taking just a few thousand routes on the
3750 and trying to do multipath over, say 4xGigE, the 'router' will
fail and you will see up to 50% packet loss. This is not something I
got off CDW's website, this is something we saw in production.
And that's without ACLs, NetFlow, 100s of peering sessions, etc. None
of which the 3750 can do and still pass gigabits of traffic through a
layer 3 decision matrix.
Have you ever configured a 3750 to do BGP with a few gigabits running
through it? A 7600? I submit that you probably have not. And you
certainly have not done it in any but the most basic of configurations
or you would not have posted this silliness.
> Or you can keep swimming in that river in Egypt. Its up to you.
William, if that's the best flame you can come up with, perhaps I
should stop reading your posts.
Then again, given you honestly believe the only difference between a
3750 & a 7600 is the # of prefixes it can take, I'm not sure why I am
still reading your posts.
> On Jan 20, 2008 5:10 PM, Patrick W. Gilmore <patrick@ianai.net> wrote:
>> On Jan 20, 2008, at 3:34 PM, William Herrin wrote:
>>> ( [entry level router's cost attributable to prefixes]/[expected
>>> lifespan] ) / [DFZ prefix count]
>>
>> I notice you cut out the next two sentences:
>>
>> <quote>
>> In short, if the table were 50K prefixes instead of 250K, would these
>> pieces of equipment be equivalent? The answer is a blatant "no".
>> </quote>
>
> Yes, I did. Its irrelevant to the cost analysis.
We disagree.
What's more, this thing called "the real world" disagrees as well.
> The dividing line between the two classes of equipment is in the
> 8k-16k prefix range. Thus your statement is like saying, "If you drop
> the towing weight from 900 lbs to 200lbs, the 1000lb tow cable is
> still not functionally equivalent to a 100lb tow cable." That has
> something of a high "duh" factor. If you dropped the prefix count to
> 8k instead of 250k, the two pieces of equipment (virtual chassis
> stack, entry level DFZ router) would be equivalent for most DFZ router
> scenarios in which an entry-level DFZ router is used.
Drop it to 8K prefixes, then see example above.
Drop it to 2 prefixes (local LAN + default), the two routers are still
not equivalent.
I'm certain there are networks who would (do?) use 3750s if the v4
table were the size of the v6 table. But they tend to be smaller
networks, with few or no BGP customers, and not much traffic. No
'tier one' network would, and most networks their size would not.
Most networks half their size would not.
Have you ever seen the requirements put on a peering or customer
aggregation router at a large network?
I really do not have time to explain why if you do not already know.
I've spent too much time trying to explain it to you already, yet I
seem to be failing at explanations, and you just send me (pathetic)
flames back anyway. Perhaps some other poster can explain it to you.
> For cost analysis purposes, you need only consider a true/false
> condition here:
> The device supports the required prefix count.
> The device does not support the required prefix count.
Would that the world were so simple.
--
TTFN,
patrick
