[183177] in North American Network Operators' Group
Re: Drops in Core
daemon@ATHENA.MIT.EDU (Patrick W. Gilmore)
Mon Aug 17 06:10:44 2015
X-Original-To: nanog@nanog.org
From: "Patrick W. Gilmore" <patrick@ianai.net>
In-Reply-To: <CAP-guGW=jPS8kB1VdYC5YTOLmRV6zedmn+hjXDMJ0FWa4DQUyA@mail.gmail.com>
Date: Mon, 17 Aug 2015 06:10:39 -0400
To: NANOG list <nanog@nanog.org>
Errors-To: nanog-bounces@nanog.org
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?
>>>>=20
>>>> 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).
>>>=20
>>> It is unlikely packets pass through an IXP more then once.
>>=20
>> =E2=80=9CUnlikely=E2=80=9D? That=E2=80=99s putting it mildly.
>>=20
>> 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 =E2=80=9Cunlikely=E2=80=9D.
>=20
> Hi Patrick,
>=20
> 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 =E2=80=9Cbut XXX happens=E2=80=9D to me. =
And you are all correct. XXX happens.
My point was not =E2=80=9Cthis never happens=E2=80=9D. 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.
--=20
TTFN,
patrick
