6978047_2.ppt
- 1. 1 © 2003, Cisco Systems, Inc. All rights reserved. Chapter 6 Routing and Routing Protocols
- 2. 2 2 2 © 2003, Cisco Systems, Inc. All rights reserved. Objectives • Introduction to static routing • Dynamic routing overview • Routing protocols overview
- 3. 3 3 3 © 2003, Cisco Systems, Inc. All rights reserved. Overview • Routing is a set of directions to get from one network to another. • These directions are known as routes • Routes can be dynamically given to the router by another router • (or) Route can be statically assigned to the router by an administrator. • A network administrator chooses a dynamic routing protocol based upon many considerations. – the size of the network, the bandwidth of available links, the processing power of the routers, the brands and models of the routers
- 4. 4 4 4 © 2003, Cisco Systems, Inc. All rights reserved. Introduction to Routing: Route Types • Routing is the process that a router uses to forward packets toward the destination network. • A router makes decisions based upon the destination IP address of a packet. • To make the correct decisions, routers must learn how to reach remote networks.
- 5. 5 5 5 © 2003, Cisco Systems, Inc. All rights reserved. Specifying Outgoing Interface (First command)
- 6. 6 6 6 © 2003, Cisco Systems, Inc. All rights reserved. Specifying the Next-hop IP Address (Second Command)
- 7. 7 7 7 © 2003, Cisco Systems, Inc. All rights reserved. Specifying the Next-hop IP Address Continued • The administrator could enter either of two commands to accomplish this objective: specifies the outgoing interface or specifies the next-hop IP address of the adjacent router. • The only difference between the two is in the administrative distance assigned to the route by the router as it is placed in the routing table • The administrative distance is an optional parameter that gives a measure of the reliability of the route. • A lower value for the administrative distance indicates the more reliable route. • Thus, a route with a lower administrative distance will be installed before an identical route with a higher administrative distance.
- 8. 8 8 8 © 2003, Cisco Systems, Inc. All rights reserved. Specifying the Next-hop IP Address Continued • The default administrative distance when using next-hop address is 1, while the default administrative distance when using the outgoing interface is 0. • If an administrative distance other than the default is desired, a value between 0 - 255 is entered after the next-hop or outgoing interface as follows: • waycross(config)#ip route 172.16.3.0 255.255.255.0 172.16.4.1 130 • To use a static route as a backup, set a higher administrative distance than the dynamic routing protocol.
- 9. 9 9 9 © 2003, Cisco Systems, Inc. All rights reserved. Configuring Static Routes
- 10. 10 10 10 © 2003, Cisco Systems, Inc. All rights reserved. Use a Local Interface as a Gateway
- 11. 11 11 11 © 2003, Cisco Systems, Inc. All rights reserved. Using a Next-Hop Device
- 12. 12 12 12 © 2003, Cisco Systems, Inc. All rights reserved. Non-directly Connected Networks (Default Route)
- 13. 13 13 13 © 2003, Cisco Systems, Inc. All rights reserved. Verifying Static Route Configuration • The command show running-config is used to view the active configuration in RAM to verify that the static route was entered correctly. • The show ip route command is used to make sure that the static route is present in the routing table
- 14. 14 14 14 © 2003, Cisco Systems, Inc. All rights reserved. Verifying Static Route Configuration Continued
- 15. 15 15 15 © 2003, Cisco Systems, Inc. All rights reserved. Troubleshooting Static Route Configuration • The show ip route command • The ping command • The traceroute command
- 16. 16 16 16 © 2003, Cisco Systems, Inc. All rights reserved. Routed Versus Routing Protocol
- 17. 17 17 17 © 2003, Cisco Systems, Inc. All rights reserved. Routed Versus Routing Protocol Continued • A routing protocol allows one router to share information with other routers regarding the networks it knows about. • The information a router gets from another router, using a routing protocol, is used to build and maintain a routing table. • A routed protocol provides enough information to allow a packet to be forwarded from one host to another based on the addressing scheme
- 18. 18 18 18 © 2003, Cisco Systems, Inc. All rights reserved. Autonomous Systems • An autonomous system (AS) is a collection of networks under a common administration sharing a common routing strategy. • The American Registry of Internet Numbers (ARIN), a service provider, or an administrator assigns an identifying number to each AS. • This autonomous system number is a 16 bit number. • Routing protocols, such as Cisco’s IGRP, require assignment of a unique, autonomous system number.
- 19. 19 19 19 © 2003, Cisco Systems, Inc. All rights reserved. Dynamic Routing Operations
- 20. 20 20 20 © 2003, Cisco Systems, Inc. All rights reserved. Purpose of Routing Protocol • The goal of a routing protocol is to build and maintain a routing table. • This table contains the learned networks and associated ports for those networks. • Routers use routing protocols to manage information received from other routers and its interfaces. • The routing protocol learns all available routes, places the best routes into the routing table, and removes routes when they are no longer valid. • The router uses the information in the routing table to forward routed protocol packets.
- 21. 21 21 21 © 2003, Cisco Systems, Inc. All rights reserved. Purpose of Routing Protocol • The routing algorithm is fundamental to dynamic routing. • Whenever the topology of a network changes because of growth, reconfiguration, or failure, the network knowledgebase (routing table) must also change. • The network knowledgebase needs to reflect an accurate view of the new topology.
- 22. 22 22 22 © 2003, Cisco Systems, Inc. All rights reserved. Dynamic Routing Operations Continued • When all routers in an internetwork are operating with the same knowledge, the internetwork is said to have converged. • Fast convergence is desirable because it reduces the period of time in which routers would continue to make incorrect routing decisions.
- 23. 23 23 23 © 2003, Cisco Systems, Inc. All rights reserved. Classes of Routing Protocols • The distance vector routing approach determines the direction (vector) and distance to any link in the internetwork. • The link-state routing approach , also called shortest path first, recreates the exact topology of the entire internetwork.
- 24. 24 24 24 © 2003, Cisco Systems, Inc. All rights reserved. Distance Vector Concepts • Distance vector based routing algorithms are also known as Bellman-Ford algorithms
- 25. 25 25 25 © 2003, Cisco Systems, Inc. All rights reserved. Distance Vector Concepts
- 26. 26 26 26 © 2003, Cisco Systems, Inc. All rights reserved. Distance Vector Concepts
- 27. 27 27 27 © 2003, Cisco Systems, Inc. All rights reserved. Routing Metric Components
- 28. 28 28 28 © 2003, Cisco Systems, Inc. All rights reserved. Link-State Concepts
- 29. 29 29 29 © 2003, Cisco Systems, Inc. All rights reserved. Link-State Concepts Continued • Link-state algorithms are also known as Dijkstras algorithm or as SPF (shortest path first) algorithms. • Link-state routing uses: • Link-state advertisements (LSAs) – A link-state advertisement (LSA) is a small packet of routing information that is sent between routers. • Topological database – A topological database is a collection of information gathered from LSAs. • SPF algorithm – The shortest path first (SPF) algorithm is a calculation performed on the database resulting in the SPF tree. • Routing tables – A list of the known paths and interfaces.
- 30. 30 30 30 © 2003, Cisco Systems, Inc. All rights reserved. Link-State Network Discovery
- 31. 31 31 31 © 2003, Cisco Systems, Inc. All rights reserved. Link-State Topology Changes
- 32. 32 32 32 © 2003, Cisco Systems, Inc. All rights reserved. Link-State Concerns
- 33. 33 33 33 © 2003, Cisco Systems, Inc. All rights reserved. Path Determination
- 34. 34 34 34 © 2003, Cisco Systems, Inc. All rights reserved. Routing with Network Addressing
- 35. 35 35 35 © 2003, Cisco Systems, Inc. All rights reserved. IP Routing Configuration Tasks
- 36. 36 36 36 © 2003, Cisco Systems, Inc. All rights reserved. Using the router and network Commands • An example of a routing configuration is: GAD(config)#router rip GAD(config-router)#network 172.16.0.0
- 37. 37 37 37 © 2003, Cisco Systems, Inc. All rights reserved. Routing Protocols: Interior and Exterior Routing Protocols
- 38. 38 38 38 © 2003, Cisco Systems, Inc. All rights reserved. Routing Protocols Continued • Examples of IP routing protocols include: • RIP – A distance vector interior routing protocol • IGRP – Cisco's distance vector interior routing protocol • OSPF – A link-state interior routing protocol • EIGRP – Cisco’s advanced distance vector interior routing protocol • BGP – A distance vector exterior routing protocol
- 39. 39 39 39 © 2003, Cisco Systems, Inc. All rights reserved. Routing Protocols RIP • Routing Information Protocol (RIP) was originally specified in RFC 1058. Its key characteristics include the following: • It is a distance vector routing protocol. • Hop count is used as the metric for path selection. • If the hop count is greater than 15, the packet is discarded. • Routing updates are broadcast every 30 seconds, by default.
- 40. 40 40 40 © 2003, Cisco Systems, Inc. All rights reserved. Routing Protocols IGRP • Interior Gateway Routing Protocol (IGRP) is a proprietary protocol developed by Cisco. Some of the IGRP key design characteristics emphasize the following: • It is a distance vector routing protocol. • Bandwidth, load, delay and reliability are used to create a composite metric. • Routing updates are broadcast every 90 seconds, by default.
- 41. 41 41 41 © 2003, Cisco Systems, Inc. All rights reserved. Routing Protocols OSPF • Open Shortest Path First (OSPF) is a nonproprietary link-state routing protocol. The key characteristics of OSPF are as follows: • It is a link-state routing protocol. • Open standard routing protocol described in RFC 2328. • Uses the SPF algorithm to calculate the lowest cost to a destination. • Routing updates are flooded as topology changes occur.
- 42. 42 42 42 © 2003, Cisco Systems, Inc. All rights reserved. Routing Protocols EIGRP • EIGRP is a Cisco proprietary enhanced distance vector routing protocol. The key characteristics of EIGRP are as follows: • It is an enhanced distance vector routing protocol. • Uses load balancing. • Uses a combination of distance vector and link- state features. • Uses Diffused Update Algorithm (DUAL) to calculate the shortest path. • Routing updates are broadcast every 90 seconds or as triggered by topology changes.
- 43. 43 43 43 © 2003, Cisco Systems, Inc. All rights reserved. Routing Protocols BGP • Border Gateway Protocol (BGP) is an exterior routing protocol. The key characteristics of BGP are as follows: • It is a distance vector exterior routing protocol. • Used between ISPs or ISPs and clients. • Used to route Internet traffic between autonomous systems.
- 44. 44 44 44 © 2003, Cisco Systems, Inc. All rights reserved. Interior/Exterior Routing Protocols
- 45. 45 45 45 © 2003, Cisco Systems, Inc. All rights reserved. Interior/Exterior Routing Protocols Continued • Interior routing protocols are designed for use in a network whose parts are under the control of a single organization. The design criteria for an interior routing protocol require it to find the best path through the network. • An exterior routing protocol is designed for use between two different networks that are under the control of two different organizations. These are typically used between ISPs or between a company and an ISP.
- 46. 46 46 46 © 2003, Cisco Systems, Inc. All rights reserved. Summary