Bill I think your approach has some merits as a measuring stick but more stufy on this is absolutely needed. Given what I've experienced recently I think the cost per prefix is greatly undervalued. It is actually a capacity/step change model that almost equates to the same model used for core bandwidth upgrades but the core bandwidth upgrades and the cost to refresh those has made the cost per prefix a non issue for the most part. Unfortunately thats changing especially in the access and distribution layers of the network. Where for the most part there are devices that can currently cope with the bandwidth demand but can't cope with the route table size demand. I suspect any AS older than 5 years has a ton of kit that can't take the entire routing table and is causing major headaches and requiring rehoming of BGP4 customers to newer kit for no additional revenues! Delivering BGP solutions for end users is starting to get very expensive particularly for those networks with lots of smaller pops, I think some effort to look at how this might be be Regards, Neil -----Original Message----- From: William Herrin <herrin-nanog@dirtside.com> Sent: 20 January 2008 17:22 To: Patrick W. Gilmore <patrick@ianai.net> Cc: nanog@merit.edu Subject: Re: Cost per prefix [was: request for help w/ ATT and terminology] On Jan 20, 2008 9:46 AM, Patrick W. Gilmore <patrick@ianai.net> wrote:

On Jan 20, 2008, at 6:06 AM, William Herrin wrote:

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On Jan 19, 2008 11:43 PM, Patrick W. Gilmore <patrick@ianai.net> wrote:

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On Jan 19, 2008, at 12:55 PM, William Herrin wrote:

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There was some related work on ARIN PPML last year. The rough numbers suggested that the attributable economic cost of one IPv4 prefix in the DFZ (whether PI, PA or TE) was then in the neighborhood of $8000 USD per year.

I haven't seen that work, but I am guessing this number is an aggregate (i.e. every cost to everyone on the 'Net combined), not per- network? See, I'm just looking at that TWO BILLION DOLLARS PER YEAR number and thinking to myself, "um, yeah, right". :)

Patrick,

That was a worldwide total, yes. The cost per prefix per router is obviously only measured in cents per year.

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 DFZ router: $40,000 Stacked 1U layer-3 switches with similar switching capacity and port density: $10,000 Difference between the two: The switch stack can't handle the DFZ prefix count. Cost delta (attributable to the DFZ prefix count): $30,000 Expected lifespan in the DFZ of an entry-level router: 3 years Prefixes in the table: 245,000 Calculation: The LOWER BOUND for the cost per prefix per router can be calculated as: ( [entry level router's cost attributable to prefixes]/[expected lifespan] ) / [DFZ prefix count] ($30,000/3)/245,000 = $0.04 per router per year, i.e. 4 cents. Bear in mind that 4 cents per year is a LOWER BOUND. It costs AT LEAST 4 cents per router per year to carry one prefix in one DFZ router. There are also routers in the DFZ which cost $500,000 where much more than $30,000 is attributable to the prefix count.

. While there are 27K ASes ($0.30/year/AS, remember?), there are many more routers which carry a full table.

Yes, there are many more routers than ASes. In my original analysis on ARIN, I estimated that there were some 200,000 routers carrying a full table in the DFZ. The consensus at the time was that the number was closer to 150,000 than 200,000. 150,000 times 4 cents yields a LOWER BOUND economic impact of $6,000 per prefix per year, $1.5B overall. Again, that's a lower bound on the estimate. The upper bound is perhaps twice that with the highest probability cost around $8,000 per prefix per year.

Comparing cisco & Juniper's annual revenue to the cost of a prefix is like comparing Ford & GM's revenue to the cost of bulbs in headlights. Hell, most of cisco's revenue is not even related to routers doing a full table.

Of course not. However, it makes a good sanity check on the cost estimate: If the costs attributable to prefix count sums to more than their revenues then there must be an error in the math. My point was that the $8000/prefix/year estimate passes the sanity check with plenty of room to spare.

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The thread started here: http://lists.arin.net/pipermail/ppml/2007-September/008927.html It was originally an argument of about the cost of doing PI for IPv6, which according to Cisco product literature consumes twice the amount of space in the FIB as routes for IPv4.

Anyway, thanks for the link. I must be missing something seriously important to the calculation. Perhaps it includes things like human time to upgrade equipment or filters or something? I'll see how the calculation was put together.

Nope, just the numbers you see in the link. I didn't calculate cost increases due to manpower, cost reductions due to equipment reuse after its DFZ lifespan, or other factors for which data is sketchy and the likely impact to the analysis is small. Like I said: read the thread, critique the numbers and then add them up for yourself. A prefix is surprisingly expensive. If it wasn't, folks wouldn't be so concerned about the rising prefix count. Regards, Bill Herrin -- William D. Herrin herrin@dirtside.com bill@herrin.us 3005 Crane Dr. Web: <http://bill.herrin.us/> Falls Church, VA 22042-3004