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

Tue Mar 13 22:06:56 UTC 2012

On Mar 13, 8:03 am, Masataka Ohta <mo... at necom830.hpcl.titech.ac.jp>
wrote:
> 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.

Bill's analysis is quite interesting, but my initial take is that it
is somehwat flawed. It assumes that the difference between what Cisco
charges for a 7606 and a 3750G bears some resemblance to the actual
bill of materials needed to support the larger routing table. That
simply isn't the case: Cisco rightly charges what they think the
market will bear for their routers and switches.

I think a more realistic approach would be to use the cost
differential between a router model X that supports 1M routes the same
model configured to support 2M routes. Or perhaps we could look at the
street prices for TCAM expansion modules. Either would be a better
indicator of the incremental cost attributable to routing table size.
The majority of costs in a mid-to-high-end Cisco/Juniper chassis are
"sunk" and have nothing to do with the size of the routing table.

The expensive routers currently used by providers are expensive
because the market isn't that big in quantity, so they are not
commodity items. They are designed to maximize the utility of very
expensive long-haul fibers and facilities to a service provider. This
means providing a high density of high-speed interfaces which can
handle millions to billions of packets per second. They also provide
lots of features that service providers and large enterprises want,
sometimes in custom ASICs. These are features which have nothing to do
with the size of the DFZ routing table, but significantly impact the
cost of the device.

> 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.

I suppose smaller multi-homed sites can and often do take a full
table, but they don't *need* to do so. What they do need is their
routes advertised to the rest of the internet, which means they must
be in the fancy-and-currently-expensive routers somewhere upstream.

This is where the cost of long-haul fiber becomes relevant: Until we
can figure out how dig cheaper ditches and negotiate cheaper rights-of-
way, there will not be an explosion of the number of full-table
provider edge routers, because there are only so many interconnection
points where they are needed. Incremental growth, perhaps, but
physical infrastructure cannot follow an exponential growth curve.

> 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.

For consumer connections, a sub-$1000 PC would serve you fine with a
full table given the level of over-subscription involved. Even
something like Quagga or Vyatta running in a virutal machine would
suffice. Or a Linksys with more RAM. Getting your providers to speak
BGP with you on such a connection for that same $100/month will be
quite a feat. Even in your contrived case, however, the monthly
recurring charges exceed a $1000 router cost after a few months.

Enterprises pay several thousand dollars per month per link for
quality IP transit at Gigabit rates.