CS 4700 / CS 5700
Network Fundamentals
Lecture 16: IXPs
(The Underbelly of the Internet)
Revised 3/23/2015
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

Outline
Emerging Internet Trends
Internet Exchange Points (IXPs)
The Internet as a Natural System
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
You’ve learned about the TCP/IP Internet
 Simple
abstraction: Unreliable datagram transmission
 Various layers
 Ancillary services (DNS)
 Extra in-network support

So what does the Internet look like?
What does the Internet look like?
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What does the Internet look like?
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Characterization challenges
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
Limited measurements and models can hint at it
 Traceroute
does not give us a complete view
 Gao-Rexford (policy routing) doesn’t capture everything

What is the Internet actually being used for?
 Emergent
properties impossible to predict from protocols
 Requires measuring the network
 Constant evolution makes it a moving target
How is the Internet used?
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How is the Internet used?
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Measuring the capital-I Internet*
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

Measuring the Internet is hard
Significant previous work on
 Router
and AS-level topologies
 Individual link / ISP traffic studies
 Synthetic traffic demands

But limited “ground-truth” on inter-domain traffic
 Most
commercial arrangements under NDA
 Significant lack of uniform instrumentation
*Mainly borrowed stolen from Labovitz 2010
Conventional Wisdom (i.e., lies)
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
Internet is a global scale end-to-end network
 Packets
transit (mostly) unmolested
 Value of network is global addressability /reachability

Broad distribution of traffic sources / sinks

An Internet “core” exists
 Dominated
by a dozen global transit providers (tier 1)
 Interconnecting content, consumer and regional providers
Traditional view
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Traditional Internet Model
Does this still hold?
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


Emergence of ‘hyper giant’ services
How much traffic do these services contribute?
Hard to answer!
 Reading:
Labovitz 2010 tries to look at this.
How do we validate/improve this picture?
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
Measure from
 110+
ISPs / content providers
 Including 3,000 edge routers and 100,000 interfaces
 And an estimated ~25% all inter-domain traffic

Do some other validation
 Extrapolate
estimates with fit from ground-truth data
 Talk with operators
Where is traffic going?
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
Increasingly: Google and Comcast
 Tier
1 still has large fraction,
but large portion of it is to Google!
 Why?
Consolidation of Content (Grouped Origin ASN)

Consolidation of traffic
 Fewer
ASes responsible
for more of the traffic
Number of Grouped ASN
Why
isForces
this happening?
Market
Intuition
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Revenue from
Internet Transit
Source: Dr. Peering, Bill Norton
Revenue from
Internet Advertisement
Source: Interactive Advertising Bureau
Transit is dead! Long live the eyeball!
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
Commoditization of IP and Hosting / CDN




Consolidation




Bigger get bigger (economies of scale)
e.g., Google, Yahoo, MSFT acquisitions
Success of bundling / Higher Value Services – Triple and quad play, etc.
New economic models



Drop of price of wholesale transit
Drop of price of video / CDN
Economics and scale drive enterprise to “cloud”
Paid content (ESPN 3), paid peering, etc.
Difficult to quantify due to NDA / commercial privacy
Disintermediation


Direct interconnection of content and consumer
Driven by both cost and increasingly performance
New applications + ways to access them
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The shift from hierarchy to flat
Verizon
$
Tier 1 ISPs
(settlement free peering)
AT&T
$$$
Sprint
$
$
Tier 2 ISPs
Regional Access
Provider
Regional Access
Provider
$
Local Access
Provider
$
Tier 3 ISPs
$
Local Access
Provider
$
Businesses/consumers
The shift from hierarchy to flat
Verizon
Tier 1 ISPs
(settlement free peering)
AT&T
Sprint
Tier 2 ISPs
Regional Access
Provider
Regional Access
Provider
Tier 3 ISPs
Local Access
Provider
$
$
IXP
Local Access
Provider
$
Businesses/consumers
A more accurate model?
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A New Internet Model
Settlement Free
Pay for BW
Pay for access BW
Flatter and much more densely interconnected Internet
How do ASes connect?
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
Point of Presence (PoP)
 Usually
a room or a building (windowless)
 One router from one AS is physically connected to the other
 Often in big cities
 Establishing a new connection at PoPs can be expensive

Internet eXchange Points (IXP)
 Facilities
dedicated to providing presence and connectivity
for large numbers of ASes
 Many fewer IXPs than PoPs
 Economies of scale
IXPs Definition
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
Industry definition (according to Euro-IX)
A physical network infrastructure operated by a single
entity with the purpose to facilitate the exchange of
Internet traffic between Autonomous Systems
The number of Autonomous Systems connected should be
at least three and there must be a clear and open policy
for others to join.
https://www.euro-ix.net/what-is-an-ixp
IXPs worldwide
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https://prefix.pch.net/applications/ixpdir/
Inside an IXP
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
Connection fabric
 Can
provide illusion of all-to-all
connectivity
 Lots of routers and cables

Also a route server
 Collects
and distributes routes
from participants
Structure
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IXPs offer connectivity to
ASes enable peering
Inside an IXP
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Infrastructure of an IXP (DE-CIX)
Robust infrastructure
with redundency
http://www.de-cix.net/about/topology/
IXPs – Publicly available information
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How much traffic is at IXPs?*
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
We don’t know for sure!
 Seems
to be a lot, though.
 One estimate: 43% of exchanged bytes are not visible to us
 Also 70% of peerings are invisible
*Mainly borrowed stolen from Feldmann 2012
Revised model 2012+
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