Inter-domain Routing: Today and Tomorrow

1. Inter-domain Routing: Today and Tomorrow 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/ IEEE INFOCOM 2004 Tutorial March 8, 2004

2. Outline • Overview of Inter-domain routing • Routing policies • Measuring inter-domain paths • Routing instability • BGP Beacon - measurement infrastructure • Implication on network engineering • Security issues 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 Internet Data plane: forward traffic IP traffic : Routing session Internet routing 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. routes Control plane: exchange routes Internet Data plane: forward traffic IP traffic Fail over to alternate route : Routing session Internet routing dictates application performance 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

7. Internet routing domain • Network devices under same technical and administrative control • Common routing policy • E.g., ISPs, enterprise networks

8. Autonomous System (AS) • 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

9. Internet Autonomous System 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 Qwest AT&T Sprint UUnet Level3 Level3 Level3 GNN Calren Calren Calren IP traffic Berkeley Berkeley Berkeley CNN Company University More than 14,000 ASes today

10. Internet Initiative Japan (IIJ)

11. IIJ, Tokyo

12. Telstra international

13. WorldCom (UUNet)

14. UUNet, Europe

15. Sprint, USA

16. Year end 2001 Anchorage, AK Seattle Spokane Portland Worcester Portland Minneapolis R Albany St. Paul Glenview Manchester Syracuse Cambridge Rochester Milwaukee Hartford Wayne Framingham Madison Grand Rapids Providence Providence R Buffalo RollingMeadows Birmingham Stamford Bridgeport R Harrisburg NYC Des Moines Detroit New Brunswick White Plains Oak Brook Cedar Knolls Salt LakeCity Plymouth Davenport Phil Wash.DC Pittsburgh Chicago R Sacramento Rochelle Pk Cleveland R Akron San Francisco South Bend R Hamilton Square Chicago Omaha R Las Vegas Silver Springs Dayton San Francisco Denver Columbus Newark Baltimore Freehold Kansas City Bohemia Indianapolis R R Arlington Cincinnati NYC- Bdwy Florissant Oakland R Norfolk Camden, NJ ColoradoSprings San Jose St Louis Louisville Richmond Redwood City R Raleigh Los Angeles OklahomaCity Albuquerque Nashville Greensboro Sherman Oaks Charlotte Tulsa SanBernardino Honolulu LA-Airport Blvd Little Rock Anaheim Memphis Gardena Columbia Birmingham Phoenix Norcross Dunwoody San Diego Atlanta Gateway Node Dallas Ft. Worth Backbone Node Jacksonville R Remote GSR Access Router New Orleans Austin Orlando Houston Remote Access Router R N X DS3 San Antonio Tampa Note: Connectivity and nodes shown are targeted for deployment; actual deployment may vary. Maps should not be used to predict service availability. W. Palm Beach N X OC3 R Ft. Lauderdale Ojus Ft. Lauderdale N X OC12 Miami N X OC48 San Juan PR Rev. 6-4-01 NX OC192 AT&T IP Backbone, USA

17. GARR-B

18. Gigabit research network

19. wiscnet.net GO BUCKY!

20. MIT.edu http://bgp.lcs.mit.edu/

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

22. 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)

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

24. Inter-domain routing and BGP • Static routing • Mainly for stub networks • Default routing • Small stub networks • Dynamic routing • Via BGP No need to run BGP in static routing and default routing.

25. Link state • 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

26. Vectoring • 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

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

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

29. RFC1519: Classless Inter-domain Routing (CIDR) • No implicit mask based on the class of the network • Explicit masks passed in the routing protocol • Allow aggregation and hierarchical routing

30. CIDR addressing 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

31. 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

32. 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

33. 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 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 10.20.128.10 135.120.0.1

34. Inter-domain routing with CIDR support • BGP-4 [RFC1771] • De facto EGP • Path vector protocol • Run on top of TCP for reliability • Carry routing information between ASes • Policy based routing

35. BGP basic operations • Set up BGP session • Exchange all candidate routes • Send incremental updates

36. 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

37. 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

38. 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

39. 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

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

41. I-BGP mesh I-BGP update E-BGP update I-BGP update I-BGP update

42. Make I-BGP scale for large AS • Route reflectors • Confederations

43. Route reflector E-BGP update RR RR Only best paths being sent by RR

44. Confederation AS 1000 EBGP IBGP IBGP EBGP AS 65020 AS 65010 EBGP

45. BGP updates • Three blocks • Prefix • Path attributes • Unreachable routes

46. Value Code Reference 1 ORIGIN [RFC1771] 2 AS_PATH [RFC1771] 3 NEXT_HOP [RFC1771] 4 MULTI_EXIT_DISC [RFC1771] 5 LOCAL_PREF [RFC1771] 6 ATOMIC_AGGREGATE [RFC1771] 7 AGGREGATOR [RFC1771] 8 COMMUNITY [RFC1997] 9 ORIGINATOR_ID [RFC1998] 10 CLUSTER_LIST [RFC1998] 11 DPA [Chen] 12 ADVERTISER [RFC1863] 13 RCID_PATH / CLUSTER_ID [RFC1863] 14 MP_REACH_NLRI [RFC2283] 15 MP_UNREACH_NLRI [RFC2283] 16 EXTENDED COMMUNITIES [Rosen] 17 NEW_AS_PATH [E.Chen] 18 NEW_AGGREGATOR [E.Chen] 19 SAFI Specific Attribute (SSA) [Nalawade] 20-254 Unassigned 255 reserved for development BGP attributes http://www.iana.org/assignments/bgp-parameters

47. 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 1 AS 2 135.120.0.0/16 EBGP 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

48. 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 1 AS 2 12.10.0.1 135.120.0.0/16 EBGP 12.10.0.2 10.10.0.1 12.10.0.0/30 IBGP IBGP Prefix Next hop AS path 135.120.0.0/16 12.10.0.1 1

49. Part II: Inter-domain Routing Policies

50. traffic traffic What is routing policy? ISP2 ISP1 Connectivity DOES NOT imply reachability! ISP3 ISP4 Cust1 Cust2 Policy determines how traffic can flow on the Internet