1. IP Routing Principles

2. Network-Layer Protocol Operations Each router provides network layer (routing) services X Y A B C Application Presentation Session Transport Network Data Link Physical Application Presentation Session Transport Network Data Link Physical A B C X Y Network Data Link Physical Network Data Link Physical Network Data Link Physical

3. Static versus Dynamic Routes Static route Uses a protocol route that a network administrator enters into the router Dynamic route Uses a route that a network routing protocol adjusts automatically for topology or traffic changes

4. Static Route Example Fixed route to address reflects administrator’s knowledge Point-to-point or circuit-switched connection “Stub” Network Only a single network connection with no need for routing updates B A

5. Default (static) Route Example Use if next hop is not explicitly listed in the routing table Company X Internet 10.0.0.0 172.34.56.0 Routing Table No entry for destination net Try router B default route No entry for destination net Try router B default route C B A

6. Dynamic routing

7. Adapting to Topology Change A B C D

8. Can an alternate route substitute for a failed route? X A B C D

9. Adapting to Topology Change Can an alternate route substitute for a failed route? X A B C D

10. Dynamic Routing Operations Routing protocol maintains and distributes routing information A router passes routing information to its neighbors Routing Table Routing Table Network Routing Protocol

11. Dynamic Routing Operations Routing protocol maintains and distributes routing information A router passes routing information to its neighbors Routing Table Routing Table Routing Table Routing Table Network Routing Protocol

12. Representing Distance with Metrics Information used to select the best path for routing 56 T1 A B 56 T1 Hop count Ticks Cost Hop count Ticks Cost

13. Representing Distance with Metrics Information used to select the best path for routing 56 T1 A B 56 T1 Bandwidth Delay Load Reliability MTU Bandwidth Delay Load Reliability MTU Hop count Ticks Cost Hop count Ticks Cost

14. Classes of Routing Protocols Distance Vector Hybrid Routing Link State C D B A C D B A

15. Convergence occurs when all routers use a consistent perspective of network topology After a topology changes, routers must recompute routes, which disrupts routing The process and time required for router reconvergence varies in routing protocols One Issue: Time to Convergence

16. Distance Vector Concept Pass periodic copies of routing table to neighbor routers and accumulate distance vectors C D B A CB A D Routing Table Routing Table Routing Table Routing Table Routing Table Routing Table Routing Table Routing Table

17. Link-State Concept After initial flood, pass small event-triggered link-state updates to all other routers Link-State Packets SPF Algorithm Topological Database Shortest Path First Tree Routing Table Routing Table CA D B

18. Comparing Distance Vector Routing to Link-State Routing Link-State Gets common view of entire network topology Calculates the shortest path to other routers Event-triggered updates: faster convergence Passes link-state routing updates to other routers Distance Vector Views net topology from neighbor’s perspective Adds hops from router to router Frequent, periodic updates: slow convergence Passes copies of routing table to neighbor routers

19. Share attributes of both distance-vector and link-state routing Hybrid Routing Choose a routing path based on distance vectors Converge rapidly using change-based updates Choose a routing path based on distance vectors Converge rapidly using change-based updates Balanced Hybrid Routing

20. Static Routing Advantages: predictable no additional CPU overhead no additional network overhead easy to configure Disadvantages: does not scale hard to maintain does not adapt to network changes

21. Dynamic Routing Advantages: scalability adaptability Disadvantages: increased complexity increased bandwidth overhead increased resource usage

22. Dynamic Routing Moral of the story: Use static routing where you can, use dynamic routing only where you must

23. Autonomous Systems Internetwork The big “I” Internet AS = a group of routers and their networks (administered by the same owner) AS peering

24. Routing Protocols Where is it used? Interior Gateway Protocols (IGP) RIP OSPF EIGRP (IS-IS) Exterior Gateway Protocols (EGP) BGP

25. Routing Protocols How does it work? Distance-Vector Protocols RIP EIGRP BGP Link State OSPF

26. Protocol Features RIPv2 hop count metric unreliable transport passive RIP simple

27. Protocol Features OSPF full CIDR support trust route injection hierarchical routing a smarter protocol

28. Protocol Features EIGRP more information in advertisements improved convergence properties partial and incremental updates no support for areas

29. Protocol Features BGP BGP-4: RFC 1771 created to support CIDR even more information Policy routing Reliable transport can also be used as an IGP (IBGP) high overhead

30. Real World Routing multiple routing protocols are generally necessary interior routing is a LOT different than exterior routing multi-protocol issues

31. Implementation Considerations 172.16 RIP 172.16 EIGRP RIP 172.16.0.0 AS 300 EIGRP ASBR 172.16 RIP 172.16 EIGRP Routing feedback Suboptimal path selection Routing loops Incompatible routing information Inconsistent convergence time

32. Controlling Routing Update Traffic How can we prevent routing update traffic from crossing some of these links? 172.16.7.1 172.16.7.2 172.16.6.1 172.16.6.2 172.16.5.2 172.16.5.1 172.16.4.1 172.16.4.2 172.16.1.1 172.16.1.2 172.16.3.1 172.16.3.2 172.16.2.2 172.16.2.1 172.16.9.1 172.16.10.1 172.16.11.1 Trans R200 Cen R300 R100 Rem 172.16.12.1 64Kb T-1 T-1 Frame Relay

33. Different protocols use different metrics Metrics are difficult to compare algorithmically Defining Distance

34. Different protocols use different metrics Metrics are difficult to compare algorithmically Therefore, need a selection process: 1—Which protocol do you believe the most? 2—Then decide which metric is the best Defining Distance

35. What Protocol to Believe? Connected Interface 0 Static Route1 Enhanced IGRP Summary Route5 External BGP20 Internal Enhanced IGRP90 IGRP100 OSPF110 IS-IS 115 RIP 120 EGP140 External Enhanced IGRP170 Internal BGP200 Unknown255 Route Source Default Distance

36. Routers! Cisco CRS-1 IP/MPLS Router 92 Tbps total switching capacity 1152 x OC-768c/STM-256c (40Gbps) Line cards 707 Kg, 15 KW per chassis IPv4, IPv6, MPLS

37. Routers! Juniper T640 Internet Routing Node 640 Gbps total switching capacity 770 Million packet per second forwarding 40 Gbps per slot (4 * OC-192c, 1 * OC-768c) 8 slots per rack

38. Routers! Foundry NetIron 1500 Internet Router 480 Gbps total switching capacity 178 Million packet per second forwarding 10 Gbps per slot (1 * 10G Ethernet) 15 slots per rack