measuringtheweb:* parti22contentdeliverynetworks€¦ · measuringtheweb:...

Measuring the Web: Part I -‐-‐ Content Delivery Networks

Prof. Anja Feldmann, Ph.D.

Dr. Ramin Khalili

Georgios Smaragdakis, PhD

Acknowledgement

Material presented in these slides is borrowed from presentaJons by:

Mike Freedman (Princeton University), Ravi Sundaram (Northeastern University, Akamai),

Craig Labovitz (Arbor Networks, DeepField), Fabian Bustamante (Northeastern University), Tobias Flach (University of South California)

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Today’s Internet Traffic

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– Web becomes main transport for video and everything else

– Thousands small web sites subsumed by large content providers

Single Server, Poor Performance

•  Single server – Single point of failure – Easily overloaded – Far from most clients

•  Popular content – Popular site – “Flash crowd” (aka “Slashdot effect”)

– Denial of Service aXack 4

Internet

Content Providers

End Users

The Web: Simple on the Outside…

IXP

IXP

Network Providers

Content Providers

End Users

Peering Points

…But ProblemaBc on the Inside

For TCP Distance MaXers

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UJlizing Caching: Proxy Caches

client

Proxy server

client

origin server

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8

Forward Proxy

•  Cache “close” to the client – Under administraJve control

of client-‐side AS

•  Explicit proxy – Requires configuring browser

•  Implicit/Transparent proxy – Service provider deploys an “on path” proxy – … that intercepts and handles Web requests

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client

Proxy server

client

Reverse Proxy

•  Cache “close” to server – Either by proxy run by server or in third-‐party content distribuJon network (CDN)

•  DirecJng clients to the proxy – Map the site name to the IP address of the proxy

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Proxy server

origin server

origin server

Content DistribuJon Network

•  ProacJve content replicaJon – Content provider (e.g., CNN) contracts with a CDN

•  CDN replicates the content – On many servers spread throughout the Internet

•  UpdaJng the replicas – Updates pushed to replicas when the content changes

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origin server in North America

CDN distribution node

CDN server in S. America CDN server

in Europe

CDN server in Asia

Server SelecJon Policy

•  Live server – For availability

•  Lowest load – To balance load across the servers

•  Closest – Nearest geographically, or in round-‐trip Jme

•  Best performance – Throughput, latency, …

•  Cheapest bandwidth, electricity, … 12

Requires conJnuous monitoring of liveness, load, and performance.

Monitoring includes traceroutes, pings, BGP updates etc

Server SelecJon Mechanism

•  ApplicaJon – HTTP redirecJon

•  Advantages – Fine-‐grain control – SelecJon based on client IP address

•  Disadvantages – Extra round-‐trips for TCP connecJon to server

– Overhead on the server

GET

Redirect

GET

OK

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•  RouJng – Anycast rouJng

•  Advantages – No extra round trips – Route to nearby server

•  Disadvantages – Does not consider network or server load

– Different packets may go to different servers

– Used only for simple request-‐response apps

1.2.3.0/24

1.2.3.0/24

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•  Naming – DNS-‐based server selecJon

•  Advantages – Avoid TCP set-‐up delay – DNS caching reduces overhead

– RelaJvely fine control

•  Disadvantage – Based on IP address of local DNS server

– “Hidden load” effect – DNS TTL limits adaptaJon

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1.2.3.4

1.2.3.5

DNS query

local DNS server

CDN example: Akamai

Servers at Network Edge

Content Providers

End Users

IXP

IXP

Akamai StaJsJcs

•  Distributed servers – Servers: ~150,000 – Networks: ~1,100 – Countries: ~80

•  Many customers -‐ Web portals

-‐  Streaming

-‐  E-‐commerce

•  Client requests -‐ Hundreds of billions per day

-‐ 15-‐20% of all Web traffic worldwide

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HTTP

How Akamai Uses DNS

cnn.com (content provider) DNS root server

1 2

Nearby Akamai cluster

GET index.html

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http://cache.cnn.com/foo.jpg

HTTP

Akamai cluster

Akamai global DNS server

Akamai regional DNS server

End user

HTTP

How Akamai Uses DNS

cnn.com (content provider) DNS TLD server

1 2


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DNS lookup cache.cnn.com

Akamai cluster

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4ALIAS: g.akamai.net



End user

HTTP

How Akamai Uses DNS


1 2




20

Akamai cluster

3

4 6

5

ALIAS a73.g.akamai.net

DNS lookup g.akamai.net

End user

HTTP

How Akamai Uses DNS


1 2




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Akamai cluster

3

4 6

5

8

7

DNS a73.g.akamai.net

Address 1.2.3.4

End user

HTTP

How Akamai Uses DNS


1 2




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Akamai cluster

3

4 6

5

8

7

9

GET /foo.jpg Host: cache.cnn.com

End user

HTTP

How Akamai Uses DNS


1 2




23

Akamai cluster

3

4 6

5

8

7

9

GET /foo.jpg Host: cache.cnn.com

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GET foo.jpg

End user

HTTP

How Akamai Uses DNS


1 2




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Akamai cluster

3

4 6

5

8

7

9

12 11

10 End user

HTTP

How Akamai Works: Cache Hit


1 2




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Akamai cluster

4

3

5

6 End user

OpJmizaJons to Improve Performance and Increase Cache Hit

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-‐ Terminate the connecBon close to the end-‐user -‐ UBlize proprietary protocols between the servers

Example $ dig www.audi.com

; <<>> DiG 9.6-‐ESV-‐R4-‐P3 <<>> www.audi.com ;; global opJons: +cmd ;; Got answer:

;; -‐>>HEADER<<-‐ opcode: QUERY, status: NOERROR, id: 47918 ;; flags: qr rd ra; QUERY: 1, ANSWER: 4, AUTHORITY: 8, ADDITIONAL: 8

;; QUESTION SECTION:

;www.audi.com. IN A

;; ANSWER SECTION: www.audi.com. 900 IN CNAME www.audi.com.edgesuite.net.

www.audi.com.edgesuite.net. 8850 IN CNAME a1805.r.akamai.net. a1805.r.akamai.net. 20 IN A 23.62.61.73 a1805.r.akamai.net. 20 IN A 23.62.61.65

;; AUTHORITY SECTION: r.akamai.net. 5386 IN NS n5r.akamai.net. r.akamai.net. 5386 IN NS n6r.akamai.net.

r.akamai.net. 5386 IN NS n7r.akamai.net. r.akamai.net. 5386 IN NS n3r.akamai.net. r.akamai.net. 5386 IN NS n4r.akamai.net.


;; ADDITIONAL SECTION: n5r.akamai.net. 5647 IN A 195.95.193.90

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RedirecBon

Example $ dig www.audi.com

; <<>> DiG 9.6-‐ESV-‐R4-‐P3 <<>> www.audi.com ;; global opJons: +cmd ;; Got answer:

;; -‐>>HEADER<<-‐ opcode: QUERY, status: NOERROR, id: 47918 ;; flags: qr rd ra; QUERY: 1, ANSWER: 4, AUTHORITY: 8, ADDITIONAL: 8

;; QUESTION SECTION:

;www.audi.com. IN A

;; ANSWER SECTION: www.audi.com. 900 IN CNAME www.audi.com.edgesuite.net.

www.audi.com.edgesuite.net. 8850 IN CNAME a1805.r.akamai.net. a1805.r.akamai.net. 20 IN A 23.62.61.73 a1805.r.akamai.net. 20 IN A 23.62.61.65

;; AUTHORITY SECTION: r.akamai.net. 5386 IN NS n5r.akamai.net. r.akamai.net. 5386 IN NS n6r.akamai.net.



;; ADDITIONAL SECTION: n5r.akamai.net. 5647 IN A 195.95.193.90

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RedirecBon

Try:

curl –H Host:www.audi.com hXp://23.62.61.73/index.html

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Measuring CDNs

•  UJlize a number of vantage points or Open DNS resolvers

•  Every e.g., 60 secs, each vantage point queries an appropriate URL delivered by Akamai, or CNAMES (e.g., *.akamai.net)

•  Similar technique can be used for other CDNs (e.g., Limemight)

PL Node

Akamai Edge Server 2


Akamai Low-Level DNS Server .……


Measuring CDNs By uJlizing a large number of vantage points or open resolvers it is possible to collect all the IPs of the CDNs!

Example of measurement in 2009:

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AKAMAI CDN: Country # of IP United States 16,843 United Kingdom 1,690 Japan 1,622 Germany 1,103 Netherlands 857 France 722 Australia 514 Canada 438 Sweden 396 Hong Kong SAR 370 Others 3018 Total 27,573

Limelight CDN: Country # of IP United States 2,830 Germany 314 United Kingdom 300 Netherlands 199 Japan 126 Canada 121 France 120 Hong Kong SAR 83 China 53 Australia 1 Total 4,147

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Measuring CDNs

day

night

Berkeley Purdue

Where to Measure CDN and Web traffic? OpJon 1: IXP infrastructure

Source: DE-‐CIX, 2012

  Complex system   Centralized monitoring

Internet eXchange Point (IXP)

Layer-2 switch

AS1

AS4

AS2 AS3

AS5 AS6

EsJmaJon of CDN and Web traffic

AS4

Akamai AS (AS1)

AS3

AS2

IXP

Akamai

Akamai

Akamai Akamai Link

IXP Results

•  Around 70% of the traffic is Web (Large IXP, 2012)

•  A relaJve small number of large CDNs, Hosters, and Streaming providers are responsible for >50% of the traffic

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Where to Measure CDN and Web traffic? OpJon 2: Private peering locaJons

Source: DE-‐CIX, 2012

•  ARBOR study: -‐ 110+ ISPs / content providers -‐ Including 3,000 edge routers and 100,000 interfaces -‐ And an esJmated ~25% all inter-‐domain traffic

•  AT&T Backbone study: Backbone, access, and mobile network

•  Deutsche Telekom Study: Passive measurements from 20K residenJal users

A Few Large CDNs and Datacenters are responsible for most of the Web

AT&T Study (2010)

Arbor Study (2009-‐13): ConsolidaJon of Web Traffic

%Traffic due to CDNs 2009: 25% 2011: 35% 2013: 50%

A Few Large CDNs and Datacenters are responsible for most of the Web

Deutsche Telekom Study (2010)

..and the CDN traffic increases

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