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Internet Routing: Measurement, Modeling, and Analysis

Internet Routing: Measurement, Modeling, and Analysis. ACM Sigmetrics 2005 Tutorial. Dr. Jia Wang jiawang@research.att.com AT&T Labs Research Florham Park, NJ 07932, USA http://www.research.att.com/~jiawang/. Prof. Zhuoqing Morley Mao zmao@umich.edu Department of EECS

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Internet Routing: Measurement, Modeling, and Analysis

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  1. Internet Routing: Measurement, Modeling, and Analysis ACM Sigmetrics 2005 Tutorial Dr. Jia Wang jiawang@research.att.com AT&T Labs Research Florham Park, NJ 07932, USA http://www.research.att.com/~jiawang/ • Prof. Zhuoqing Morley Mao • zmao@umich.edu • Department of EECS • University of Michigan • Ann Arbor, MI 48109, USA • http://www.eecs.umich.edu/~zmao/

  2. Outline • Overview of Inter-domain routing • Measuring inter-domain paths • BGP Measurement • BGP Modeling Our opinions should not be taken to represent AT&T policies

  3. Part I: Overview of Inter-domain Routing

  4. Internet • Loose cooperative effort of Internet Service Providers (ISPs) • E.g., AT&T, Sprint, UUNet, AOL • Best effort service • Connectedness • Anyone connected to the Internet can exchange traffic with anyone else connected to the Internet

  5. routes Control plane: exchange routes Fail over to alternate route : Routing session Internet routing Internet Data plane: forward traffic IP traffic rusty.cs.berkeley.edu IP=169.229.62.116 Prefix=169.229.0.0/16 www.cnn.com IP=64.236.16.52 Prefix=64.236.16.0/20

  6. Internet routing domain • Autonomous routing domain • Network devices under same technical and administrative control • Common routing policy • E.g., ISPs, enterprise networks • Autonomous system • Autonomous routing domain with an AS number (ASN) • AS numbers: 16 bits integer • Public AS number: 1 – 64511 • Private AS number: 64512 – 65535 • Examples • AT&T: 7018, 6431, … • Sprint: 1239, 1240, … • MIT: 3

  7. company company Qwest Qwest UUnet UUnet Sprint Sprint AT&T AT&T ISP ISP ISP ISP ISP ISP ISP ISP ISP University University business business business ISP ISP ISP ISP ISP ISP ISP ISP ISP ISP ISP ISP ISP ISP ISP More than 20,000 ASes today Internet Autonomous System Qwest AT&T Sprint UUnet Level3 Level3 Level3 GNN Calren Calren Calren IP traffic Berkeley Berkeley Berkeley CNN company University

  8. Calren GNN CNN Level3 Internet routing architecture Intra-domain routing Inter-domain routing IPtraffic Internet Berkeley

  9. Intra-domain routing • Run within a certain network infrastructure • Optimize routes taken between points within a network • Internal Gateway Protocols (IGPs) • Metrics based • OSPF (Open Shortest Path First) • RIP (Routing Information Protocol) • IS-IS (Intermediate System to Intermediate System)

  10. Inter-domain routing • Run between networks • Provide full connectivity of entire Internet • External Gateway Protocol (EGP) • Policy based • BGP (Border Gateway Protocol)

  11. Link state protocols • Examples: OSPF, IS-IS • Based on Dijkstra’s shortest path computation • Each router periodically floodsimmediate reachability information to other routers • Fast convergence • High communication and computation overhead • Not scalable for large networks • Requires periodic refreshes

  12. Vectoring protocols • Distance vs. Path Vector • Distance: hop count (RIP) • Path: entire path (BGP) • Helps identify loops • Supports policy-based routing based on path • Minimal communication overhead • Takes longer to converge, i.e., in proportion to the maximum path length

  13. Link state vs. vectoring Link state Vectoring IGP EGP BGP is a path vector protocol

  14. Classful addressing • IPv4: 32 bits • Five classes of networks Improve scaling factor of routing in the Internet => classless

  15. CIDR: Classless Inter-domain Routing (RFC1519) • No implicit mask based on the class of the network • Explicit masks passed in the routing protocol • Allow aggregation and hierarchical routing IP address: 12.70.0.0 Mask: 255.255.252.0 Address 00001100 00100110 00000000 00000000 00001100 00100110 00000000 00000000 Mask 11111111 11111111 11000000 00000000 11111111 11111111 11000000 00000000 Host identifier Network prefix CIDR representation: 12.70.0.0/22

  16. Address aggregation Internet 12.70.3.0/24 12.70.0.0/24 ISP A 12.70.1.0/24 ISP B 12.71.0.0/16 12.70.2.0/24 12.70.0.0/22 12.71.0.0/16

  17. Routing and forwarding • Routing • The decision process of choosing optimal path that is consistent with the administrative or technical policy • Forwarding • The act of receiving a packet, doing a lookup, and copying a packet to the next hop

  18. Classless forwarding Internet 12.70.0.20 10.20.128.10 10.20.128.1 10.20.0.1 IP traffic 10.20.1.1 135.120.0.1 Prefix Next hop 12.70.0.0/24 10.20.0.1 12.70.0.0/16 10.20.1.1 12.0.0.0/8 10.20.128.1 0.0.0.0 10.20.128.10

  19. Inter-domain routing with CIDR support • BGP-4 [RFC1771] • De facto EGP • Carry routing information between ASes • Path vector protocol • Policy based routing • Run on top of TCP for reliability • Basic operations • Set up BGP session • Exchange all candidate routes • Send incremental updates

  20. Establish BGP session Establish neighboring session between 12.10.0.1 and 12.10.0.2 TCP 179 12.10.0.1 12.10.0.2 Prefix Next hop 135.120.0.0/24 10.128.0.1 68.35.0.0/16 10.192.1.1 Prefix Next hop 12.70.0.0/24 10.20.0.1 12.9.0.0/16 10.20.1.1

  21. Exchange all candidate routes 12.70.0.0/24 10.20.0.1 12.9.0.0/16 10.20.1.1 12.10.0.1 12.10.0.2 135.120.0.0/24 10.128.0.1 68.35.0.0/16 10.192.1.1 Prefix Next hop 135.120.0.0/24 10.128.0.1 68.35.0.0/16 10.192.1.1 12.70.0.0/24 10.20.0.1 12.9.0.0/16 10.20.1.1 Prefix Next hop 12.70.0.0/24 10.20.0.1 12.9.0.0/16 10.20.1.1 135.120.0.0/24 10.128.0.1 68.35.0.0/16 10.192.1.1

  22. Send incremental updates Withdraw 12.9.0.0/16 12.10.0.1 12.10.0.2 Prefix Next hop 135.120.0.0/24 10.128.0.1 68.35.0.0/16 10.192.1.1 12.70.0.0/24 10.20.0.1 12.9.0.0/16 10.20.1.1 Prefix Next hop 12.70.0.0/24 10.20.0.1 12.9.0.0/16 10.20.1.1 135.120.0.0/24 10.128.0.1 68.35.0.0/16 10.192.1.1

  23. BGP messages • OPEN: set up a peering session • UPDATE: announce new routes or withdraw previously announced routes • NOTIFICATION: shut down a peering session • KEEPALIVE: confirm active connection at regular interval

  24. Internal vs. external BGP I-BGP update Internet I-BGP E-BGP update I-BGP update E-BGP AS B AS C AS A

  25. Route reflectors Confederations AS 1000 E-BGP update EBGP RR RR IBGP IBGP EBGP AS 65020 AS 65010 EBGP Scaling I-BGP for large AS Only best paths being sent by RR

  26. Establish connectivity Prefix Next hop AS path 135.120.0.0/16 12.10.0.5 2 1 AS 3 Prefix Next hop AS path 135.120.0.0/16 12.10.0.1 1 12.10.0.6 IBGP EBGP 12.10.0.5 AS 2 AS 1 EBGP 135.120.0.0/16 12.10.0.2 IBGP 12.10.0.1 IBGP Prefix Next hop AS path 135.120.0.0/16 12.10.0.1 1

  27. IGP and BGP working together Prefix Next hop AS path 135.120.0.0/16 12.10.0.1 1 AS 3 Prefix Next hop 12.10.0.0/30 10.10.0.1 135.120.0.0/16 10.10.0.1 12.10.0.6 IBGP EBGP 12.10.0.5 AS 2 AS 1 12.10.0.1 EBGP 135.120.0.0/16 12.10.0.2 10.10.0.1 IBGP 12.10.0.0/30 IBGP Prefix Next hop AS path 135.120.0.0/16 12.10.0.1 1

  28. traffic traffic Policy routing ISP2 ISP1 Connectivity DOES NOT imply reachability! ISP3 ISP4 Cust1 Cust2 Policy determines how traffic can flow on the Internet

  29. BGP routing process Apply input policy Apply output policy Select best route Routes advised to peers Routes received from peers Best routes Routing table Forwarding table BGP is not shortest path routing!

  30. Best route selection • Highest local preference • Shortest AS path • Lowest MED (Multi-Exit-Discriminator) • I-BGP < E-BGP • Lowest I-BGP cost to E-BGP egress • Tie breaking rules

  31. Best route selection • Highest local preference • To enforce economical relationships between domains • Shortest AS path • Lowest MED (Multi-Exit-Discriminator) • I-BGP < E-BGP • Lowest I-BGP cost to E-BGP egress • Tie breaking rules

  32. Best route selection • Highest local preference • Shortest AS path • Compare the quality of routes, assuming shorter AS-path length is better • Lowest MED (Multi-Exit-Discriminator) • I-BGP < E-BGP • Lowest I-BGP cost to E-BGP egress • Tie breaking rules

  33. Best route selection • Highest local preference • Shortest AS path • Lowest MED (Multi-Exit-Discriminator) • To implement “cold potato” routing between neighboring domains • I-BGP < E-BGP • Lowest I-BGP cost to E-BGP egress • Tie breaking rules

  34. Best route selection • Highest local preference • Shortest AS path • Lowest MED (Multi-Exit-Discriminator) • I-BGP < E-BGP • Prefer EBGP routes to IBGP routes • Lowest I-BGP cost to E-BGP egress • Tie breaking rules

  35. Best route selection • Highest local preference • Shortest AS path • Lowest MED (Multi-Exit-Discriminator) • I-BGP < E-BGP • Lowest I-BGP cost to E-BGP egress • Prefer routes via the nearest IGP neighbor • To implement “hot potato” routing • Tie breaking rules

  36. Best route selection • Highest local preference • Shortest AS path • Lowest MED (Multi-Exit-Discriminator) • I-BGP < E-BGP • Lowest I-BGP cost to E-BGP egress • Tie breaking rules • Router ID based: lowest router ID • Age based: oldest route

  37. BGP route propagation • Not all possible routes propagate • Commercial relationships determine policies for • Route import • Route selection • Route export

  38. Typical AS relationships • Provider-customer • customer pay money for transit • Peer-peer • typically exchange respective customers’ traffic for free • Siblings • Mutual transit agreement • Provide connectivity to the rest of the Internet for each other

  39. AS relationships translate into BGP export rules • Export to a provider or a peer • Allowed: its routes and routes of its customers and siblings • Disallowed: routes learned from other providers or peers • Export to a customer or a sibling • Allowed: its routes, the routes of its customers and siblings, and routes learned from its providers and peers

  40. Which AS paths are legal? • Valley-free: • After traversing a provider-customer or peer-peer edge, cannot traverse a customer-provider or peer-peer edge • Invalid path: >= 2 peer links, downhill-uphill, downhill-peer, peer-uphill

  41. Example of valley-free paths [1 2 3], [1 2 6 3] are valley-free X X [1 4 3], [1 4 5 3] are not valley free

  42. Inferring AS relationships • Identify the AS-level hierarchy of Internet • Not shortest path routing • Predict AS-level paths • Traffic engineering • Understand the Internet better • Correlate with and interpret BGP update • Identify BGP misconfigurations • E.g., errors in BGP export rules

  43. Existing approaches • On inferring Autonomous Systems Relationships in the Internet, by L. Gao, IEEE Global Internet, 2000. • Characterizing the Internet hierarchy from multiple vantage points, by L. Subramanian, S. Agarwal, J. Rexford, and R. Katz, IEEE Infocom, 2002. • Computing the Types of the Relationships between Autonomous Systems, by G. Battista, M. Patrignani, and M. Pizzonia, IEEE Infocom, 2003. • On AS-level Path Inference, by Z. Mao, L. Qiu, J. Wang, and Y. Zhang, ACM Sigmetrics, 2005.

  44. Policy routing causes path inflation • End-to-end paths are significantly longer than necessary • Why? • Topology and routing policy choices within an ISP, between pairs of ISPs, and across the global Internet • Peering policies and interdomain routing lead to significant inflation • Interdomain path inflation is due to lack of BGP policy to provide convenient engineering of good paths across ISPs

  45. Path inflation • Based on [Mahajan03] • Comparing actual Internet paths with hypothetical “direct” link

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