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CSE534- Fundamentals of Computer Networking Lecture 12-13: Internet Connectivity + IXPs (The Underbelly of the Internet) Based on slides by D. Choffnes.

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Presentation on theme: "CSE534- Fundamentals of Computer Networking Lecture 12-13: Internet Connectivity + IXPs (The Underbelly of the Internet) Based on slides by D. Choffnes."— Presentation transcript:

1 CSE534- Fundamentals of Computer Networking Lecture 12-13: Internet Connectivity + IXPs (The Underbelly of the Internet) Based on slides by D. Choffnes (NEU), C. Labovitz, A. Feldmann, revised by P. Gill Spring 2015.

2  Internet Connectivity  The shift from hierarchy to flat  Measuring the shift  IXPs Outline 2

3 The Internet as a Natural System 3  You’ve learned about the TCP/IP Internet  Simple abstraction: Unreliable datagram transmission  Various layers  Ancillary services (DNS)  Extra in-network support  So 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

4 Conventional Wisdom (i.e., lies) 4  Internet is a global scale end-to-end network  Packets transit (mostly) unmodified  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

5 Does this still hold? 5  Emergence of ‘hyper giant’ services  Changing the way we think about interdomain connectivity!  How much traffic do these services contribute?  What is their connectivity?  Hard to answer!

6 The shift from hierarchy to flat Local Access Provider Local Access Provider Regional Access Provider Regional Access Provider AT&T Sprint Verizon Regional Access Provider Regional Access Provider Tier 1 ISPs (settlement free peering) Tier 2 ISPs Tier 3 ISPs Local Access Provider Local Access Provider Businesses/consumers $ $ $ $ $ $ $$$$

7 The shift from hierarchy to flat Local Access Provider Local Access Provider Regional Access Provider Regional Access Provider AT&T Sprint Verizon Regional Access Provider Regional Access Provider Tier 1 ISPs (settlement free peering) Tier 2 ISPs Tier 3 ISPs Local Access Provider Local Access Provider Businesses/consumers $ IXP$ $

8  Internet Connectivity  The shift from hierarchy to flat  Measuring the shift  IXPs Outline 8

9 First saw this in 2008  traceroute to (Google)  ms ms ms  ms ms ms  ms ms ms  ms ms ms  ms ms ms  ms ms ms  ms ms ms  ms ms ms  ms ms ms LINX(UK) UK ISP

10 We wondered how prevalent this was 10  Idea: Traceroute to large content providers see where the traceroute enters their network  Optional reading: The Flattening Internet Topology: Natural Evolution, Unsightly Barnacles or Contrived Collapse? Gill et al.

11 What we saw: Paths with no Tier 1s 11 60% of paths with no tier 1 ISP (30 out of 50)

12 Relative degree of top content providers 12 We saw many more neighboring ASes for the top content providers (not just a few providers) We saw many more neighboring ASes for the top content providers (not just a few providers)

13 An initial map of connectivity 13 Google

14 This study suggested something was happening… 14  …But didn’t exhaustively measure the phenomenon  Only traceroute data from a limited set of VPs  50 paths to each domain  Observing and measuring flattening requires measurements of the entire Internet topology

15 Measuring the Internet’s topology 15  What do we mean by topology?  Internet as graph  Edges? Nodes?  Node = Autonomous System (AS); edge = connection.  Edges labeled with business relationship  Customer  Provider  Peer -- Peer SBU AT&T Sprint

16 So how do we measure this graph? 16  Passive approach: BGP route monitors  Coverage of the topology  Amount of visibility provided by each neighbor  Active approach: Traceroute  From where?  Traceroute gives series of IP addresses not ASes  Active approach: TransitPortal  Much more control over what we see  …scalability/coverage?

17 Passive approach: BGP Route Monitors 17  Receive BGP announcements from participating ASes at multiple vantage points Regional ISP

18 Going from BGP Updates to a Topology 18  Example update:  TIME: 03/22/11 12:10:45  FROM: AS7018  TO: AS6447  ASPATH:  /20 AT&T (AS7018) it telling Routeviews (AS 6447) about this route. AT&T (AS7018) it telling Routeviews (AS 6447) about this route. This /20 prefix can be reached via the above path

19 Going from BGP Updates to a Topology 19  Key idea  The business relationships determine the routing policies  The routing policies determine the paths that are chosen  So, look at the chosen paths and infer the policies  Example: AS path “ ” implies  AS 4134 allows AS 7018 to reach AS 9318  China Telecom allows AT&T to reach Hanaro Telecom  Each “triple” tells something about transit service

20 Why are peering links hard to see?  The challenge: do not reflect complete connectivity  BGP announcements do not reflect complete connectivity information  They are an agreement to transit traffic for the AS they are advertised to… Local ISP Regional ISP Small business Small business Local ISP, Google $ Local ISP, Small business no valley routing policy lack of monitors in stub ASes up to 90% Combination of no valley routing policy and a lack of monitors in stub ASes mean missing up to 90% of peering links of content providers! (Oliveria et al. 2008)

21 Active approach: Traceroute 21  Issue: Need control over end hosts to run traceroute  How to get VPs?   Collection of O(100) servers that will run traceroute  Hosted by ISPs/other network operators (e.g. universities)  RIPE Atlas  Distribute specialized hardware to volunteers  O(1000s) of probes  Dasu  Bittorrent plug in that does measurements  O(200) ASes with Dasu clients

22 Where the sidewalk ends (CoNEXT 2009) (1/2)  Idea: Leverage traceroutes from P2P clients to extend the AS graph Local ISP1 Regional ISP Local ISP2 $ Mock traceroute: IP ISP 1 (client1) … IP ISP 1 (router) IP ISP 2 (router) … IP ISP 2 (client2)

23 Where the sidewalk ends (CoNEXT 2009) (2/2)  23,914 new AS links  13% more customer provider links  41% more peering links

24 Review: 3 techniques for measuring AS topology 24  Passive approach: BGP route monitors  Coverage of the topology  Amount of visibility provided by each neighbor  Active approach: Traceroute  From where?  Traceroute gives series of IP addresses not ASes  Active approach: TransitPortal  Much more control over what we see  …scalability/coverage?

25 Active Approach: Transit Portal 25  Motivation: Traceroute/BGP monitors will only show us paths that are in use…  … not full connectivity  Need to explore back up paths to find all the full AS- level topology  Transit Portal solution:  AS + Prefix controlled by researchers  Border of the research AS made up by participating institutions  BGPMux at each institution acts as border router, multiplexes TP users, sends BGP updates out.

26 Transit Portal Coverage 26  Now also at SBU!

27 Using TP to explore connectivity 27  Similar idea as LIFEGUARD … B B C C D D A A Prefix Traceroute VP TP Prefix B, TP Prefix C, TP Prefix D, TP Prefix A, B, TP Prefix TP

28 Using TP to explore connectivity 28  Similar idea as LIFEGUARD … B B C C D D A A Prefix Traceroute VP TP, B, TP Prefix C, TP, B, TP Prefix D, TP, B, TP Prefix A, C, TP, B, TP Prefix TP

29 Using TP to explore connectivity 29  Similar idea as LIFEGUARD … B B C C D D A A Prefix Traceroute VP TP, B, C, TP Prefix D, TP, B, C, TP Prefix A, D, TP, B, C TP Prefix TP This is a simplified view … in reality AS prepending to keep path lengths from impacting decisions This is a simplified view … in reality AS prepending to keep path lengths from impacting decisions

30 This isn’t the end of the story… 30  ASes may have more complex business relationships  Geographic relationships E.g., peer in one region, provider in another  Per-prefix relationships E.g., Amazon announcing a prefix only to a specific provider AS14618 enterprise portion of Amazon

31 The outputs … p2c p2c p2c p2c p2c p2c p2c p2c p2c p2c p2c 15413…

32  Internet Connectivity  The shift from hierarchy to flat  Measuring the shift  IXPs  Based on slides by A. Feldmann Outline 32

33 How do ASes connect? 33  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  Facilities dedicated to providing presence and connectivity for large numbers of ASes  Many fewer IXPs than PoPs  Economies of scale

34 IXPs Definition 34  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

35 Internet eXchange Points 35

36 IXPs worldwide 36 https://prefix.pch.net/applications/ixpdir/

37 Inside an IXP 37  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

38 IXPs -- Peering 38  Peering – Why? E.g., Giganews:  “Establishing open peering arrangements at neutral Internet Exchange Points is a highly desirable practice because the Internet Exchange members are able to significantly improve latency, bandwidth, fault-tolerance, and the routing of traffic between themselves at no additional costs.”  IXPs – Four types of peering policies  Open Peering – inclination to peer with anyone, anywhere Most common!  Selective Peering – Inclination to peer, with some conditions  Restrictive Peering – Inclination not to peer with any more entities  No Peering – No, prefer to sell transit  Policy.html

39 Interesting observations (from required reading) 39

40 Interesting observations (2) 40


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