Shim6, was: Re: filtering /48 is going to be necessary

Owen DeLong owen at delong.com
Tue Mar 13 19:18:33 UTC 2012


On Mar 13, 2012, at 6:03 AM, Masataka Ohta wrote:

> Ryan Malayter wrote:
> 
>>> If the number of routes in DFZ is, say, 100, many routers and
>>> hosts will be default free
>> 
>> For quite some time, a sub-$2000 PC running Linux/BSD has been able to
>> cope with DFZ table sizes and handle enough packets per second to
>> saturate two or more if the prevalent LAN interfaces of the day.
> 
> What if, you run windows?
> 

Why would you want to run windows on a box you're trying to use as a
router? That's like trying to invade Fort Knox with a bag of plastic soldiers.

Leo's point is that you can build/buy a DFZ capable router for less than $2,000.

If you run windows, the box will be more expensive, less capable, and less
reliable. If that's what you want, knock yourself out, but, it's hardly relevant
to the discussion at hand.

>> The reason current routers in the core are so expensive is because of
>> the 40 gigabit interfaces, custom ASICs to handle billions of PPS,
>> esoteric features, and lack of competition.
> 
> The point of
> 
> 	http://bill.herrin.us/network/bgpcost.html
> 
> was that routers are more expensive because of bloated routing
> table.
> 
> If you deny it, you must deny its conclusion.
> 

To a certain extent you are right. I believe that Bill's analysis and
his conclusions are deeply flawed in many ways.

However, he is marginally correct in that the high cost of core
DFZ routers is the product of the large forwarding table multiplied by
the cost per forwarding entry in a high-pps high-data-rate system.
Further adding to this is the fact that high-rate (pps,data) routers
generally need to distribute copies of the FIB to each line card
so the cost per forwarding entry is further multiplied by the number
of line cards (and in some cases, the number of modules installed
on each line card).

>> The fact that long-haul fiber is very expensive to run limits the
>> number of DFZ routers more than anything else.
> 
> Given that global routing table is bloated because of site
> multihoming, where the site uses multiple ISPs within a city,
> costs of long-haul fiber is irrelevant.
> 

Long-haul meaning anything that leaves the building. Yes, it's
a poor choice of terminology, but, if you prefer, the costs of last-
mile fiber apply equally to Leo's point.

>> Why not take a default
>> route and simplify life when you're at the end of a single coax link?
> 
> That's fine.
> 
>> If your lucky enough to have access to fiber from multiple providers,
>> the cost of a router which can handle a full table is not a major
>> concern compared with your monthly recurring charges.
> 
> As it costs less than $100 per month to have fiber from a
> local ISP, having them from multiple ISPs costs a lot less
> is negligible compared to having routers with a so bloated
> routing table.

$100/month * 2 = $200/month. $200/month pays for a DFZ
capable router every year.

That's means that the cost of 2*fiber costs quite a bit more than
the cost of the router.

There is a difference between a DFZ router and a core router.

I personally run a DFZ router for my personal AS. I don't personally
own or run a core router for my personal AS. The fact that people
conflate the idea of a DFZ router with the idea of a core router is
part of the problem and a big part of where Bill's cost structure
analysis breaks, as you pointed out.

Small to medium businesses that want to multihome can easily
do so with relatively small investments in equipment which are
actually negligible compared to the telecom costs for the multiple
connections.

Owen





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