estimation of number of DFZ IPv4 routes at peak in the future

Christopher Morrow morrowc.lists at
Sun Mar 13 14:42:28 CDT 2011

On Sun, Mar 13, 2011 at 2:11 PM, Jeff Wheeler <jsw at> wrote:
> On Sun, Mar 13, 2011 at 1:27 PM, Christopher Morrow
> <morrowc.lists at> wrote:
>> there's probably a different need in TOR and BO/SOHO locations than
>> core devices, eh?
> In today's backbone, this is certainly true.  Feature-driven upgrades
> shouldn't be much of a factor for "P boxes" today, because modern
> networks have the option of simply label-switching in the core (just
> like 1990s networks could ATM/Frame-switch) without doing much of
> anything else.  Feature-driven upgrades should be largely confined to
> "PE boxes."

not everyone drinks the mpls koolaide... so it's not always 'just a
label switch' and depending upon how large your PE mesh is, there are
still some challenges in scaling this. MPLS also only shifts the
burden to another place, if you provide ip-transit and you need a full
table you'll have to put those routes somewhere. Sure the 'core' may
not need that info, but the edge likely does, yes? Have 100g customers
today? planning on having them in the next ~8/12/18 months?

> For the same reason, upgrading a P box should be easy, not hard.
> After all, it's just label-switching.  In today's backbones, it should

upgrades aren't hard, unless you get yourself into a SPOF situation
with the 'P' router(s)... mechanically the upgrades aren't hard.
Cost-wise though it could be, it depends upon your particular cost
structure I imagine.

> be more practical than ever to buy the most cost-effective box needed
> for now and the predictable near-term.  Cost per gigabit continues to
> fall.  Buying dramatically more capacity than is planned to be
> necessary sinks capital dollars into a box that does nothing but
> depreciate.

The discussion at the RAWS meeting, and which seems to hold true for
larger networks, is that a box lives in the network for ~5-7 years.
First, for the core-class device today, in the core, then
progressively further to the edge. Some thought goes into 'today I
have X requirements, I can project based on some set of metrics I'll
have X+Y tomorrow.'

> I realize that organizationally-painful budgeting and purchasing
> processes often drive networks to buy the biggest thing available.
> Vendors understand this, too: they love to sell you a much bigger box
> than you need just because upgrading is hard to get approved so you
> don't want to do it any more frequently than necessary, even when that
> behavior is detrimental to cash-flow and bottom line.  The more broken
> your organization, the more you need to spend extra money on "too big"
> boxes.  Sounds pretty self-defeating, doesn't it?

sometimes... sometimes it's just business. I suppose the point here is
that a box doesn't live ~12 months or even 24, it lives longer.
Planning that horizon today is problematic when a box today (even the
largest box) tops out just north of 2m routes (v4, I forget the mix
v4/6 numbers). your network design may permit you to side step that
issue in places, but planning for that number is painful today.


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