[183162] in North American Network Operators' Group
Re: Drops in Core
daemon@ATHENA.MIT.EDU (Patrick W. Gilmore)
Sun Aug 16 08:23:50 2015
X-Original-To: nanog@nanog.org
From: "Patrick W. Gilmore" <patrick@ianai.net>
In-Reply-To: <20150816121518.GK72293@-.true.nl>
Date: Sun, 16 Aug 2015 08:23:44 -0400
To: NANOG list <nanog@nanog.org>
Errors-To: nanog-bounces@nanog.org
On Aug 16, 2015, at 8:15 AM, Job Snijders <job@instituut.net> wrote:
> On Sun, Aug 16, 2015 at 08:00:55AM -0400, Patrick W. Gilmore 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:
>>=20
>>>> 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
> There is another scenario (which unfortunatly is not that uncommon)
> where packets could traverse two IXPs, and no transit is sold over any
> of those two IXs.
>=20
> Imagine the following:
>=20
> Network A purchases transit from network B & network C. Network B &
> Network C peer with each other via an IXP. Network A announces a /16 =
to
> network B but 2 x /17 to network C. Network D peers with B via an IX
> (and not with C) and receives the /16 from B, but note that internally
> network B has two more specifics covering the /16 received from C and
> the /16 itself. Network B will export the /16 (received from customer)
> but not the /17s (received over peering) to its peers.
>=20
> Because of longest prefix matching, network B will route the packets
> received from network D over an IXP, towards network C, again over an
> IXP.=20
>=20
> This phenomenon is described extensively in the following
> Internet-Draft:
>=20
> https://tools.ietf.org/html/draft-ietf-grow-filtering-threats-07
Good point.
Although I have trouble believing it is very common, in the sense that I =
do not believe it is a large number of packets or percent of traffic.
To be clear, I fully believe people are doing the more specifics to =
provider B but not C. Sometimes there is even a good reason for it =
(although probably not usually). However, most of the Internet will send =
traffic directly to B, or even A - especially since most packets are =
sourced from CDNs[*].
--=20
TTFN,
patrick
[*] I=E2=80=99m counting in-house CDNs like Google, Netflix, and Apple =
as =E2=80=9CCDNs=E2=80=9D here. Before anyone bitches, trust me, I am =
probably more aware of the difference between those and a =E2=80=9Creal=E2=
=80=9D CDN than nearly anyone else. But those distinctions are =
orthogonal to the discussion at hand.
