Re: Drops in Core

["Patrick W. Gilmore" <patrick () ianai net>]

On Aug 16, 2015, at 8:44 AM, William Herrin <bill () herrin us> wrote:
> On Sun, Aug 16, 2015 at 8:00 AM, Patrick W. Gilmore <patrick () ianai net> wrote:
> > On Aug 15, 2015, at 1:41 PM, Job Snijders <job () instituut net> wrote:
> > > On Sat, Aug 15, 2015 at 11:01:56PM +0530, Glen Kent wrote:

> > > > Is there a paper or a presentation that discusses the drops in the core?
> > > >
> > > > If i were to break the total path into three legs -- the first, middle
> > > > and the last, then are you saying that the probability of packet loss
> > > > is perhaps 1/3 in each leg (because the packet passes through
> > > > different IXes).
> > >
> > > It is unlikely packets pass through an IXP more then once.
> >
> > “Unlikely”? That’s putting it mildly.
> >
> > Unless someone is selling transit over an IX, I do not see how it
> > can happen. And I would characterize transit over IXes far more
> > pessimistically than “unlikely”.
>
> Hi Patrick,
>
> I'm told it happens relatively often in networks supporting a lot of
> schools. Being an unpaid pass-through for schools paying other ISPs
> functions as a loss-leader that attracts more schools as customers.

Lots of people have mentioned “but XXX happens” to me. And you are all correct. XXX happens.

My point was not “this never happens”. Just those other topologies are a tiny, tiny fraction of the packets flowing on 
the Internet.

Most packets flow from CDNs to broadband. And those packets flow mostly direct (on-net or PNI), or over a _single_ IXP. 
Corner cases exist, but they are just that - corner cases.

-- 
TTFN,
patrick