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CCNA 2 Module 6 Routing and Routing Protocols © 2003, Cisco Systems, Inc. All rights reserved. 1 Objectives • Introduction to static routing • Dynamic routing overview • Routing protocols overview © 2003, Cisco Systems, Inc. All rights reserved. 2 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 © 2003, Cisco Systems, Inc. All rights reserved. 3 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. © 2003, Cisco Systems, Inc. All rights reserved. 4 Specifying Outgoing Interface (First command) © 2003, Cisco Systems, Inc. All rights reserved. 5 Specifying the Next-hop IP Address (Second Command) © 2003, Cisco Systems, Inc. All rights reserved. 6 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. © 2003, Cisco Systems, Inc. All rights reserved. 7 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. © 2003, Cisco Systems, Inc. All rights reserved. 8 Configuring Static Routes © 2003, Cisco Systems, Inc. All rights reserved. 9 Use a Local Interface as a Gateway © 2003, Cisco Systems, Inc. All rights reserved. 10 Using a Next-Hop Device © 2003, Cisco Systems, Inc. All rights reserved. 11 Non-directly Connected Networks (Default Route) © 2003, Cisco Systems, Inc. All rights reserved. 12 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 © 2003, Cisco Systems, Inc. All rights reserved. 13 Verifying Static Route Configuration Continued © 2003, Cisco Systems, Inc. All rights reserved. 14 Troubleshooting Static Route Configuration • The show ip route command • The ping command • The traceroute command © 2003, Cisco Systems, Inc. All rights reserved. 15 Routed Versus Routing Protocol © 2003, Cisco Systems, Inc. All rights reserved. 16 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 © 2003, Cisco Systems, Inc. All rights reserved. 17 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. © 2003, Cisco Systems, Inc. All rights reserved. 18 Dynamic Routing Operations © 2003, Cisco Systems, Inc. All rights reserved. 19 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. © 2003, Cisco Systems, Inc. All rights reserved. 20 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. © 2003, Cisco Systems, Inc. All rights reserved. 21 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. © 2003, Cisco Systems, Inc. All rights reserved. 22 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. © 2003, Cisco Systems, Inc. All rights reserved. 23 Distance Vector Concepts • Distance vector based routing algorithms are also known as Bellman-Ford algorithms © 2003, Cisco Systems, Inc. All rights reserved. 24 Distance Vector Concepts © 2003, Cisco Systems, Inc. All rights reserved. 25 Distance Vector Concepts © 2003, Cisco Systems, Inc. All rights reserved. 26 Routing Metric Components © 2003, Cisco Systems, Inc. All rights reserved. 27 Link-State Concepts © 2003, Cisco Systems, Inc. All rights reserved. 28 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. © 2003, Cisco Systems, Inc. All rights reserved. 29 Link-State Network Discovery © 2003, Cisco Systems, Inc. All rights reserved. 30 Link-State Topology Changes © 2003, Cisco Systems, Inc. All rights reserved. 31 Link-State Concerns © 2003, Cisco Systems, Inc. All rights reserved. 32 Path Determination © 2003, Cisco Systems, Inc. All rights reserved. 33 Routing with Network Addressing © 2003, Cisco Systems, Inc. All rights reserved. 34 IP Routing Configuration Tasks © 2003, Cisco Systems, Inc. All rights reserved. 35 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 © 2003, Cisco Systems, Inc. All rights reserved. 36 Routing Protocols: Interior and Exterior Routing Protocols © 2003, Cisco Systems, Inc. All rights reserved. 37 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 © 2003, Cisco Systems, Inc. All rights reserved. 38 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. © 2003, Cisco Systems, Inc. All rights reserved. 39 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. © 2003, Cisco Systems, Inc. All rights reserved. 40 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. © 2003, Cisco Systems, Inc. All rights reserved. 41 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 linkstate features. • Uses Diffused Update Algorithm (DUAL) to calculate the shortest path. • Routing updates are broadcast every 90 seconds or as triggered by topology changes. © 2003, Cisco Systems, Inc. All rights reserved. 42 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. © 2003, Cisco Systems, Inc. All rights reserved. 43 Interior/Exterior Routing Protocols © 2003, Cisco Systems, Inc. All rights reserved. 44 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. © 2003, Cisco Systems, Inc. All rights reserved. 45 Summary © 2003, Cisco Systems, Inc. All rights reserved. 46