1 © 2003, Cisco Systems, Inc. All rights reserved. CCNA 2 Module 6 Routing and Routing Protocols

222 © 2003, Cisco Systems, Inc. All rights reserved. Objectives Introduction to static routing Dynamic routing overview Routing protocols overview

333 © 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

444 © 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.

555 © 2003, Cisco Systems, Inc. All rights reserved. Specifying Outgoing Interface (First command)

666 © 2003, Cisco Systems, Inc. All rights reserved. Specifying the Next-hop IP Address (Second Command)

777 © 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.

888 © 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 is entered after the next-hop or outgoing interface as follows: waycross(config)#ip route To use a static route as a backup, set a higher administrative distance than the dynamic routing protocol.

999 © 2003, Cisco Systems, Inc. All rights reserved. Configuring Static Routes

10 © 2003, Cisco Systems, Inc. All rights reserved. Use a Local Interface as a Gateway

11 © 2003, Cisco Systems, Inc. All rights reserved. Using a Next-Hop Device

12 © 2003, Cisco Systems, Inc. All rights reserved. Non-directly Connected Networks (Default Route)

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 © 2003, Cisco Systems, Inc. All rights reserved. Verifying Static Route Configuration Continued

15 © 2003, Cisco Systems, Inc. All rights reserved. Troubleshooting Static Route Configuration The show ip route command The ping command The traceroute command

16 © 2003, Cisco Systems, Inc. All rights reserved. Routed Versus Routing Protocol

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 © 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 © 2003, Cisco Systems, Inc. All rights reserved. Dynamic Routing Operations

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 © 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 © 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 © 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 © 2003, Cisco Systems, Inc. All rights reserved. Distance Vector Concepts Distance vector based routing algorithms are also known as Bellman-Ford algorithms

25 © 2003, Cisco Systems, Inc. All rights reserved. Distance Vector Concepts

26 © 2003, Cisco Systems, Inc. All rights reserved. Distance Vector Concepts

27 © 2003, Cisco Systems, Inc. All rights reserved. Routing Metric Components

28 © 2003, Cisco Systems, Inc. All rights reserved. Link-State Concepts

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 © 2003, Cisco Systems, Inc. All rights reserved. Link-State Network Discovery

31 © 2003, Cisco Systems, Inc. All rights reserved. Link-State Topology Changes

32 © 2003, Cisco Systems, Inc. All rights reserved. Link-State Concerns

33 © 2003, Cisco Systems, Inc. All rights reserved. Path Determination

34 © 2003, Cisco Systems, Inc. All rights reserved. Routing with Network Addressing

35 © 2003, Cisco Systems, Inc. All rights reserved. IP Routing Configuration Tasks

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

37 © 2003, Cisco Systems, Inc. All rights reserved. Routing Protocols: Interior and Exterior Routing Protocols

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 © 2003, Cisco Systems, Inc. All rights reserved. Routing Protocols RIP Routing Information Protocol (RIP) was originally specified in RFC 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 © 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 © 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 Uses the SPF algorithm to calculate the lowest cost to a destination. Routing updates are flooded as topology changes occur.

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 © 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 © 2003, Cisco Systems, Inc. All rights reserved. Interior/Exterior Routing Protocols

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 © 2003, Cisco Systems, Inc. All rights reserved. Summary