1. Chapter 5 IP Routing Routing Protocol vs. Routed Protocol

2. 2 Topics Review –Internetworking –Path determination –Router –IP Address Routed and Routing Protocols –Network protocols Routed Routing –Interior Protocols vs. Exterior Protocols Routing Protocol Activity

3. Review Router and IP Address

4. 4 Internetworking

5. 5 Path determination Path determination is the process that the router uses to choose the next hop in the path for the packet to travel to its destination based on the link bandwidth, hop, delay...

6. 6 Router A router is a type of internetworking device that passes data packets between networks, based on Layer 3 addresses. A router has the ability to make intelligent decisions regarding the best path for delivery of data on the network.

7. 7 IP addresses IP addresses are implemented in software, and refer to the network on which a device is located. IP addressing scheme, according to their geographical location, department, or floor within a building. Because they are implemented in software, IP addresses are fairly easy to change.

8. 8 Router and Bridge

9. 9 Router connections Routers connect two or more networks, each of which must have a unique network number in order for routing to be successful. The unique network number is incorporated into the IP address that is assigned to each device attached to that network.

10. 10 Router Interface

11. 11 Router function

12. 12 Router function (cont.1) Strips off the data link header, carried by the frame. (The data link header contains the MAC addresses of the source and destination.) Strips off the data link header, carried by the frame. (The data link header contains the MAC addresses of the source and destination.)

13. 13 Router function (cont.2) Examines the network layer address to determine the destination network.

14. 14 Router function (cont.3) Consults its routing tables to determine which of its interfaces it will use to send the data, in order for it to reach its destination network.

15. 15 Router function (cont.4) Send the data out interface B1, the router would encapsulate the data in the appropriate data link frame.

16. 16 Router Interface example Interface is a router ’ s attachment to a network, it may also be referred to as a port. In IP routing. Each interface must have a separate, unique network address.

17. ROUTED AND ROUTING PROTOCOLS

18. 18 Network protocols In order to allow two host communicate together through internetwork, they need a same network protocol. Protocols are like languages. IP is a network layer protocol.

19. 19 Network protocol operation

20. 20 Routed protocol Protocols that provide support for the network layer are called routed or routable protocols. IP is a network layer protocol, and because of that, it can be routed over an internetwork.

21. 21 Protocol addressing variations

22. 22 Three important routed protocols TCP/IP:04 bytes –Class A: 1 byte network + 3 bytes host –Class B: 2 bytes network + 2 bytes host –Class C: 3 bytes network + 1 byte host IPX/SPX:10 bytes –4 bytes network + 6 bytes host AppleTalk:03 bytes –2 bytes network + 1 byte host

23. 23 Non-routable protocol Non-routable protocols are protocols that do not support Layer 3. The most common of these non-routable protocols is NetBEUI. NetBEUI is a small, fast, and efficient protocol that is limited to running on one segment.

24. 24 Addressing of a routable protocol

25. 25 Routing table 131.108.1.0E0 131.108.2.0E1 131.108.3.0E2

26. 26 Multi-protocol routing

27. 27 Classification #1: Static and Dynamic Static routes: –The network administrator manually enter the routing information in the router. Dynamic routes: –Routers can learn the information from each other on the fly. –Using routing protocol to update routing information. –RIP, IGRP, EIGRP, OSPF …

28. 28 Static routes

29. 29 Dynamic routes

30. 30 Static vs. dynamic routes Static routes: –For hiding parts of an internetwork. –To test a particular link in a network. –For maintaining routing tables whenever there is only one path to a destination network. Dynamic routes: –Maintenance of routing table. –Timely distribution of information in the form of routing updates. –Relies on routing protocol to share knowledge. –Routers can adjust to changing network conditions.

31. 31 Routing protocol Routing protocols determine the paths that routed protocols follow to their destinations. Routing protocols enable routers that are connected to create a map, internally, of other routers in the network or on the Internet.

32. 32 Routed vs. Routing protocol Routing protocols determine how routed protocols are routed protocols are routed

33. 33 Classification #2: IGP and EGP Dynamic routes. Interior Gateway Protocols (RIP, IGRP, EIGRP, OSPF): –Be used within an autonomous system, a network of routers under one administration, like a corporate network, a school district's network, or a government agency's network. Exterior Gateway Protocols (EGP, BGP): –Be used to route packets between autonomous systems.

34. 34 IGP IGP IGP vs. EGP EGP

35. 35 Classification #3: DVP and LSP Distance-Vector Protocols (RIP, IGRP): –View network topology from neighbor’s perspective. –Add distance vectors from router to router. –Frequent, periodic updates. –Pass copy of routing tables to neighbor routers. Link State Protocols (OSPF): –Gets common view of entire network topology. –Calculates the shortest path to other routers. –Event-triggered updates. –Passes link state routing updates to other routers.

36. 36 Distance vector routing

37. 37 Link state routing

38. Part II

39. 39 © 2004 Cisco Systems, Inc. All rights reserved. ICND v2.2—3-39 Distance Vector Routing

40. 40 Outline –Overview –Distance Vector Route Selection –Routing Information Maintenance –How Routing Inconsistencies Occur with Distance Vector Routing Protocols –Count to Infinity Prevention –Techniques to Eliminate Routing Loops –Implementation of Techniques to Eliminate Routing Loops –Summary

41. 41 Routers pass periodic copies of their routing table to neighboring routers and accumulate distance vectors. Distance Vector Routing Protocols

42. 42 Routers discover the best path to destinations from each neighbor. Sources of Information and Discovering Routes

43. 43 Selecting the Best Route with Metrics

44. 44 Updates proceed step by step from router to router. Maintaining Routing Information

45. 45 Each node maintains the distance from itself to each possible destination network. Inconsistent Routing Entries

46. 46 Slow convergence produces inconsistent routing. Inconsistent Routing Entries (Cont.)

47. 47 Router C concludes that the best path to network 10.4.0.0 is through router B. Inconsistent Routing Entries (Cont.)

48. 48 Router A updates its table to reflect the new but erroneous hop count. Inconsistent Routing Entries (Cont.)

49. 49 The hop count for network 10.4.0.0 counts to infinity. Count to Infinity

50. 50 A limit is set on the number of hops to prevent infinite loops. Defining a Maximum

51. 51 Packets for network 10.4.0.0 bounce (loop) between routers B and C. Routing Loops

52. 52 It is never useful to send information about a route back in the direction from which the original information came. Split Horizon

53. 53 Routers advertise the distance of routes that have gone down to infinity. Route Poisoning

54. 54 Poison reverse overrides split horizon. Poison Reverse

55. 55 The router keeps an entry for the “possibly down state” in the network, allowing time for other routers to recompute for this topology change. Holddown Timers

56. 56 The router sends updates when a change in its routing table occurs. Triggered Updates

57. 57 Eliminating Routing Loops

58. 58 Eliminating Routing Loops (Cont.)

59. 59 Eliminating Routing Loops (Cont.)

60. 60 Eliminating Routing Loops (Cont.)

61. 61 Eliminating Routing Loops (Cont.)

62. 62 Eliminating Routing Loops (Cont.)

63. 63 Summary –Distance vector routing protocols generate periodic routing updates addressed to directly connected routing devices. Routers running a distance vector routing protocol send periodic updates even if there are no changes in the network. –When a router receives an update from a neighbor’s router, the router compares the update with its own routing table. The router adds the cost of reaching the neighbor’s router to the path cost reported by the neighbor to establish a new metric. –Routing inconsistencies occur if slow internetwork convergence or a new configuration causes incorrect routing entries.

64. 64 Summary (Cont.) –Distance vector protocols define infinity as some maximum number. The routing protocol then permits the routing table update loop until the metric exceeds its maximum allowed value. –There are five techniques for eliminating routing loops on distance vector routing networks: split horizon, route poisoning, poison reverse, holddown timers, and triggered updates. –All five techniques can be used together to eliminate routing loops in area networks.

65. 65 © 2004 Cisco Systems, Inc. All rights reserved. ICND v2.2—3-65 Link-State and Balanced Hybrid Routing

66. 66 Outline –Overview –How Routing Information is Maintained with Link State –Link-State Routing Protocol Algorithms –Benefits and Limitations of Link-State Routing –When to Use Link-State Routing Protocols –Balanced Hybrid Routing –Summary

67. 67 After initial flood of LSAs, link-state routers pass small event-triggered link- state updates to all other routers. Link-State Routing Protocols

68. 68 Drawbacks to Link-State Routing Protocols Initial discovery may cause flooding. Link-state routing is memory- and processor-intensive.

69. 69 How Routing Information Is Maintained

70. 70 Link-State Routing Protocol Algorithms

71. 71 Minimizes routing table entries Localizes impact of a topology change within an area Link-State Network Hierarchy Example

72. 72 Link-State Routing Protocol Algorithms

73. 73 Advantages and Disadvantages of Link-State Routing

74. 74 Comparing Distance Vector and Link-State Routing

75. 75 Benefits of Link-State Routing –Fast convergence: Changes are reported immediately by the affected source. –Robustness against routing loops: Routers know the topology. Link-state packets are sequenced and acknowledged. –Through careful (hierarchical) network design, resources can be optimalized.

76. 76 Caveats to Link-State Routing –Significant demands for resources: Memory (three tables: adjacency, topology, forwarding) CPU (Dijkstra’s algorithm can be intensive, especially when a lot of instabilities are present) –Requires very strict network design –Problems with partitioning of areas –Configuration generally simple, but can be complex when tuning various parameters and when design is complex –Troubleshooting easier than in distance vector routing

77. 77 Shares attributes of both distance vector and link-state routing Balanced Hybrid Routing

78. 78 Summary –Link-state routing protocols collect routing information from all other routers in the network. After all information is collected, each router calculates its own best path to all destinations in the network. –Link-state algorithms maintain a complex database of the network topology. Knowledge of the network routers and of how they interconnect is achieved through the exchange of LSAs with other routes in a network. –Using triggered, flooded updates, link-state protocols can immediately report changes in the network topology, leading to fast convergence times. In contrast, the use of many different databases can require a significant amount of memory.

79. 79 Summary (Cont.) –To avoid an excessive use of memory, a strict hierarchical network design is required. The configuration of link-state networks should remain simple to avoid tuning. –Balanced hybrid routing protocols combine aspects of both distance vector and link-state protocols.

80. Routing Protocol

81. 81 RIP Most popular. Interior Gateway Protocol. Distance Vector Protocol. Only metric is number of hops. Maximum number of hops is 15. Updates every 30 seconds. Doesn ’ t always select fastest path. Generates lots of network traffic.

82. 82 IGRP and EIGRP Cisco proprietary. Interior Gateway Protocol. Distance Vector Protocol. Metric is compose of bandwidth, load, delay and reliability. Maximum number of hops is 255. Updates every 90 seconds. EIGRP is an advanced version of IGRP, that is hybrid routing protocol.

83. 83 OSPF Open Shortest Path First. Interior Gateway Protocol. Link State Protocol. Metric is compose of cost, speed, traffic, reliability, and security. Event-triggered updates.

84. End Chapter V