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

1© 2003, Cisco Systems, Inc. All rights reserved.

CCNA 2 Module 6 Routing and Routing Protocols


Objectives

• Introduction to static routing

• Dynamic routing overview

• Routing protocols overview


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


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.


Specifying Outgoing Interface (First command)


Specifying the Next-hop IP Address (Second Command)


Specifying the Next-hop IP AddressContinued

• 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.


Specifying the Next-hop IP AddressContinued

• 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.


Configuring Static Routes


Use a Local Interface as a Gateway


Using a Next-Hop Device


Non-directly Connected Networks (Default Route)


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


Verifying Static Route ConfigurationContinued


Troubleshooting Static Route Configuration

• The show ip route command

• The ping command

• The traceroute command


Routed Versus Routing Protocol


Routed Versus Routing ProtocolContinued

• 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


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.


Dynamic Routing Operations


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.


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.


Dynamic Routing OperationsContinued

• 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.


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.


Distance Vector Concepts

• Distance vector based routing algorithms are also known as Bellman-Ford algorithms






Routing Metric Components


Link-State Concepts


Link-State ConceptsContinued

• 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.


Link-State Network Discovery


Link-State Topology Changes


Link-State Concerns


Path Determination


Routing with Network Addressing


IP Routing Configuration Tasks


Using the router and network Commands

• An example of a routing configuration is:

GAD(config)#router ripGAD(config-router)#network 172.16.0.0


Routing Protocols: Interior and Exterior Routing Protocols


Routing ProtocolsContinued

• 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


Routing ProtocolsRIP

• 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.


Routing ProtocolsIGRP

• 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.


Routing ProtocolsOSPF

• 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.


Routing ProtocolsEIGRP

• 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.


Routing ProtocolsBGP

• 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.


Interior/Exterior Routing Protocols


Interior/Exterior Routing ProtocolsContinued

• 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.


Summary

Documents

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