1. © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public ITE PC v4.0 Chapter 1 1 Introduction to Dynamic Routing Protocol Routing Protocols and Concepts – Chapter 3

2. ITE PC v4.0 Chapter 1 2 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Dynamic Routing Protocols  Function(s) of Dynamic Routing Protocols: -Dynamically share information between routers. -Automatically update routing table when topology changes. -Determine best path to a destination.

3. ITE PC v4.0 Chapter 1 3 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Dynamic Routing Protocols  The purpose of a dynamic routing protocol is to: -Discover remote networks -Maintaining up-to-date routing information -Choosing the best path to destination networks -Ability to find a new best path if the current path is no longer available

4. ITE PC v4.0 Chapter 1 4 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Dynamic Routing Protocols  Components of a routing protocol –Data Structures: Tables or databases for their operations, kept in RAM. –Algorithm An algorithm is a finite list of steps used in accomplishing a task. Used for processing routing information and for best- path determination. –Routing protocol messages Discover neighboring routers. Exchange, learn and maintain accurate network routing information.

5. ITE PC v4.0 Chapter 1 5 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Dynamic Routing Protocols Advantages over Static Routes: –Less administrative overhead. –Scales better. –Less prone to configuration errors.  Advantages of static routing -Easy to configure -No extra resources are needed -More secure  Disadvantages of static routing -Network changes require manual reconfiguration -Does not scale well in large topologies

6. ITE PC v4.0 Chapter 1 6 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Classifying Routing Protocols  Dynamic routing protocols are grouped according to characteristics. Examples include: -RIP -IGRP -EIGRP -OSPF -IS-IS -BGP

7. ITE PC v4.0 Chapter 1 7 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Classifying Dynamic Routing Protocols Interior Gateway Exterior Gateway Distance Vector Link State Path Vector ClassfulRIPIGRPEGP ClasslessRIPv2EIGRPOSPFv2IS-ISBGPv4 IPv6RIPng EIGRP for IPv6 OSPFv3 IS-IS for IPv6 BGPv4 for IPv6

8. ITE PC v4.0 Chapter 1 8 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Classifying Dynamic Routing Protocols Concept of Autonomous Systems (AS): Autonomous System is a group of routers under the control of a single authority. A network or group of networks identified and administered as a single entity.

9. ITE PC v4.0 Chapter 1 9 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Classifying Dynamic Routing Protocols IGP vs. EGP Routing Protocols: Allow one AS to exchange routing information with another AS. Allow routers within an AS to exchange information.

10. ITE PC v4.0 Chapter 1 10 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Classifying Routing Protocols  Types of routing protocols: -Interior Gateway Protocols (IGP) -Exterior Gateway Protocols (EGP)

11. ITE PC v4.0 Chapter 1 11 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Classifying Routing Protocols  Interior Gateway Routing Protocols (IGP) -Used for routing inside an autonomous system & used to route within the individual networks themselves. -Examples: RIP, EIGRP, OSPF  Exterior Routing Protocols (EGP) -Used for routing between autonomous systems -Example: BGPv4

12. ITE PC v4.0 Chapter 1 12 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Interior Gateway Exterior Gateway Distance Vector Link State Path Vector ClassfulRIPIGRPEGP ClasslessRIPv2EIGRPOSPFv2IS-ISBGPv4 IPv6RIPng EIGRP for IPv6 OSPFv3 IS-IS for IPv6 BGPv4 for IPv6 Interior Gateway Exterior Gateway Distance Vector Link State Path Vector ClassfulRIPIGRPEGP ClasslessRIPv2EIGRPOSPFv2IS-ISBGPv4 IPv6RIPng EIGRP for IPv6 OSPFv3 IS-IS for IPv6 BGPv4 for IPv6 Classifying Dynamic Routing Protocols

13. ITE PC v4.0 Chapter 1 13 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Classifying Routing Protocols  IGP: Comparison of Distance Vector & Link State Routing Protocols Distance vector –routes are advertised as vectors of distance & direction. –incomplete view of network topology. –Generally, periodic updates. Link state –complete view of network topology is created. –updates are not periodic.

14. ITE PC v4.0 Chapter 1 14 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Distance Vector and Link State Distance Vector: –Routes are advertised as vectors of distance and direction. Distance: –Is defined in terms of a metric. »Hop Count: The number of routers between the source and destination networks. Direction: –Is simply the next-hop router or exit interface. –Routing updates usually consist of periodic updates of the entire routing table. (e.g.. Routing Information Protocol - RIP – every 30 seconds)

15. ITE PC v4.0 Chapter 1 15 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Distance Vector and Link State Distance Vector: or update timer expires

16. ITE PC v4.0 Chapter 1 16 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Distance Vector and Link State Link State: –A Link State routing protocol can create a complete map of the network topology. –A link-state router: Receives an update. Builds a topology database. Uses a Shortest Path First (SPF) algorithm to create its view of the network. Builds the routing table. (e.g.. Open Shortest Path First - OSPF)

17. ITE PC v4.0 Chapter 1 17 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Interior Gateway Exterior Gateway Distance Vector Link State Path Vector ClassfulRIPIGRPEGP ClasslessRIPv2EIGRPOSPFv2IS-ISBGPv4 IPv6RIPng EIGRP for IPv6 OSPFv3 IS-IS for IPv6 BGPv4 for IPv6 Classifying Dynamic Routing Protocols

18. ITE PC v4.0 Chapter 1 18 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Classifying Routing Protocols  Classful routing protocols –Do NOT send subnet mask in routing updates –Classful routing protocols include RIPv1 and IGRP. –VLSM and CIDR are not possible.  Classless routing protocols –Do send subnet mask in routing updates. –Classless routing protocols are RIPv2, EIGRP, OSPF, IS-IS, BGP –VLSM and CIDR are not possible.

19. ITE PC v4.0 Chapter 1 19 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Interior Gateway Exterior Gateway Distance Vector Link State Path Vector ClassfulRIPIGRPEGP ClasslessRIPv2EIGRPOSPFv2IS-ISBGPv4 IPv6RIPng EIGRP for IPv6 OSPFv3 IS-IS for IPv6 BGPv4 for IPv6 Classifying Dynamic Routing Protocols

20. ITE PC v4.0 Chapter 1 20 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Classifying Routing Protocols  Convergence is defined as when all routers’ routing tables are at a state of consistency The network has converged when all routers have complete and accurate information about the network. Convergence time is the time it takes routers to share information, calculate best paths, and update their routing tables.

21. ITE PC v4.0 Chapter 1 21 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Dynamic Routing Protocols and Convergence Convergence: –Generally: Slower Convergence: RIP Faster Convergence: EIGRP and OSPF

22. ITE PC v4.0 Chapter 1 22 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Introduction to Dynamic Routing Protocols Metrics ? ? ?

23. ITE PC v4.0 Chapter 1 23 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Purpose of a Metric There are times when a router will have multiple paths to the same destination. Metrics are a way to measure and/or compare routes to determine which route is the best path. ? To route to..

24. ITE PC v4.0 Chapter 1 24 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Purpose of a Metric The route chosen will depend on two things: –The routing protocol in use. –The metric used by the routing protocol. ? To route to..

25. ITE PC v4.0 Chapter 1 25 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Routing Protocols Metrics  Metrics used in IP routing protocols -Bandwidth -Delay -Hop count -Load

26. ITE PC v4.0 Chapter 1 26 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Routing Protocols Metrics  The Metric Field in the Routing Table  Metric used for each routing protocol -RIP - hop count -IGRP & EIGRP - Bandwidth (used by default), Delay (used by default), Load, Reliability -IS-IS & OSPF – Cost, Bandwidth Metric

27. ITE PC v4.0 Chapter 1 27 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Metrics and Routing Protocols Routing Information Protocol (RIP): –Uses hop count as its metric. Lower is better. 172.16.2.0/24 Network 172.16.2.0 is: 1 hop via R2 2 hops via R3 This is the route I will use.

28. ITE PC v4.0 Chapter 1 28 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Metrics and Routing Protocols Open Shortest Path First (OSPF): –Uses bandwidth as its metric. Faster is better. 172.16.2.0/24 The route to network 172.16.2.0/24 is: 56 Kbps through R2 1.54 Kbps through R3 This is the route I will use.

29. ITE PC v4.0 Chapter 1 29 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Metric Filed in the Routing Table The routing table displays the metric for each dynamic and static route. –Dynamic routes with the lowest metric are installed by routing protocols. –Static routes always have a metric of 0.

30. ITE PC v4.0 Chapter 1 30 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Metric Field in the Routing Table All routers are running RIP. R2 has a route to 192.168.8.0 and is 2 hops away.

31. ITE PC v4.0 Chapter 1 31 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Load Balancing What happens when two or more routes to the same destination have identical metric values? The router load balances among all equal-cost paths.

32. ITE PC v4.0 Chapter 1 32 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Routing Protocols Metrics  Load balancing This is the ability of a router to distribute packets among multiple same cost paths

33. ITE PC v4.0 Chapter 1 33 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Introduction to Dynamic Routing Protocols Administrative Distance

34. ITE PC v4.0 Chapter 1 34 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Purpose of Administrative Distance (AD) Routers learn about adjacent networks that are directly connected and about remote networks by using static routes and dynamic routing protocols. A router might learn of a route to the same network from more than one source. Three types of Routing Sources. –Direct Connect –Static –Dynamic Routing Protocol Route SourceAD Direct Connect0 Static1 EIGRP Summary5 External BGP20 Internal EIGRP90 OSPF110 IS-IS115 RIP120 External EIGRP170 Internal BGP200

35. ITE PC v4.0 Chapter 1 35 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Purpose of Administrative Distance (AD) Administrative Distance is used to determine which route is to be installed in the routing table. The route that has the lower AD will be preferred over the route with the higher AD and will be added to the routing table. The term trustworthy is commonly used when defining administrative distance. –The lower the administrative distance value, the more “trustworthy” the route. Route SourceAD Direct Connect0 Static1 EIGRP Summary5 External BGP20 Internal EIGRP90 OSPF110 IS-IS115 RIP120 External EIGRP170 Internal BGP200

36. ITE PC v4.0 Chapter 1 36 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Multiple Routing Sources For Example: –A route to a network is learned by the configuration of a static route. –Another route (or the same route) to the same network is learned when OSPF is enabled on the router. Static Route AD = 1 OSPF AD = 110 –The static route will be added to the routing table and the route learned from OSPF will be ignored. Route SourceAD Direct Connect0 Static1 EIGRP Summary5 External BGP20 Internal EIGRP90 OSPF110 IS-IS115 RIP120 External EIGRP170 Internal BGP200

37. ITE PC v4.0 Chapter 1 37 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Administrative Distance of a Route  Identifying the Administrative Distance (AD) in a routing table It is the first number in the brackets in the routing table

38. ITE PC v4.0 Chapter 1 38 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Administrative Distance of a Route  Dynamic Routing Protocols Administrative distance is an integer value from 0 to 255. The lower the value the more preferred the route source. Administrative distance is an integer value from 0 to 255. The lower the value the more preferred the route source.

39. ITE PC v4.0 Chapter 1 39 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Multiple Routing Sources While not as common, R2 above has learned routes to network 192.168.6.0/24 from EIGRP (AD 90) and from RIP (AD 120). The route learned from EIGRP will be installed in the routing table.

40. ITE PC v4.0 Chapter 1 40 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Verifying Administrative Distance (AD) show ip route AD = 0

41. ITE PC v4.0 Chapter 1 41 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Verifying Administrative Distance (AD) show ip protocols

42. ITE PC v4.0 Chapter 1 42 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Static Routes and Administrative Distance Static Route AD = 1 –After directly connected networks (AD = 0), static routes are the most preferred route source.

43. ITE PC v4.0 Chapter 1 43 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Static Routes and Administrative Distance Routing table display depends on how you issued the command. The AD for both of these is 1! Exit Interface: ip route 172.16.3.0 255.255.255.0 serial 0/0/0 Next-hop Address: ip route 172.16.3.0 255.255.255.0 192.168.1.1

44. ITE PC v4.0 Chapter 1 44 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Directly Connected and Administrative Distance Appear in the routing table as soon as the interface is active with an IP address and subnet mask. –AD = 0 is the most preferred route. Cannot be changed No other type of route can have AD = 0. There is no better route for a router than having one of its interfaces directly connected to that network.

45. ITE PC v4.0 Chapter 1 45 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Summary  Metrics are used by dynamic routing protocols to calculate the best path to a destination.  Administrative distance is an integer value that is used to indicate a router’s “trustworthiness”  Components of a routing table include: -Route source -Administrative distance -Metric

46. ITE PC v4.0 Chapter 1 46 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public

47. ITE PC v4.0 Chapter 1 47 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Distance Vector and Link State Link State: