© 2007 Cisco Systems, Inc. All rights reserved. Cisco PublicITE PC v4.0Chapter 1 1

Introduction to Dynamic Routing Protocol

Routing Protocols and Concepts – Chapter 3

Sandra Coleman, CCNA, CCAI

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Objectives Describe the role of dynamic routing protocols and

place these protocols in the context of modern network design.

Identify several ways to classify routing protocols.

Describe how metrics are used by routing protocols and identify the metric types used by dynamic routing protocols.

Determine the administrative distance of a route and describe its importance in the routing process.

Identify the different elements of the routing table.

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Overview of dynamic routing protocols

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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.

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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

-They can NOW SHARE information with each other!

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Dynamic Routing Protocols Components of a routing protocol

Algorithm

In the case of a routing protocol, algorithms are used for facilitating routing information and best path determination

Routing protocol messages

These are messages for discovering neighbors and exchange of routing information

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Dynamic Routing Protocols Advantages of static routing

-It can backup multiple interfaces/networks on a router

-Easy to configure

-No extra resources are needed

-More secure

-Administrator maintains control over the routing process

Disadvantages of static routing-Network changes require manual reconfiguration

-Does not scale well in large topologies

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Classifying Routing Protocols Dynamic routing protocols are grouped according to

characteristics. Examples include:

-RIP

-IGRP

-EIGRP

-OSPF

-IS-IS

-BGP

Autonomous System is a group of routers under the control of a single authority.

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Classifying Routing Protocols Types of routing protocols:

-Interior Gateway Protocols (IGP) – routing within an AS

-Exterior Gateway Protocols (EGP) – routing between AS’s

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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

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IGP ProtocolsDistance vector (RIP, EIGRP)– routes are advertised as vectors of distance & direction.– incomplete view of network topology. (only sees its neighbors)– Generally, periodic updates. (30-, 90-seconds, etc.) are sent ONLY

to neighboring routers– Work best in a simple, flat network or a hub-and-spoke topology–Admins do NOT have to be very knowledgable

Link state (OSPF)– complete view of network topology is created. (Sees EVERYONE

– like a map)– Knowledgeable administrators– updates are not periodic. (triggered by a change)– Quicker convergence– Should be used in larger organizations with more than 5 routers

(especially if some of them are NOT Cisco routers)

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Classifying Routing Protocols

Classful routing protocolsDo NOT send subnet mask in

routing updates

DO NOT support VLSM

RIPv1 and IGRP

Classless routing protocols

DO send subnet mask in

routing updates.

Supports VLSM

RIPv2, EIGRP, OSPF, IS-IS, BGP

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Classifying Routing Protocols Convergence is defined as when all routers’ routing

tables are at a state of consistency (They all have the SAME level of knowledge)

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Convergence

Fast convergence is VERY desirable, especially when using dynamic routing protocols.

WHY? Routers could make incorrect forwarding decisions if the topology is NOT converged.

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Routing Protocols Metrics Metric

A value used by a routing protocol to determine which routes are better than others.

See the RIP example below!

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Routing Protocols Metrics Metrics used in IP routing protocols

-Bandwidth – Highest preferred (EIGRP)

-Cost – value determined by IOS or by network admin.

-Delay – time to traverse a path

-Hop count - # routers packet must pass through (RIP)

-Load – traffic utilization on a certain link

-Reliability – probability of a link failure (based on an algorithm)

You don’t need to understand all of these right now, we’ll discuss them as we get to the protocol they apply to.

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Metric Example

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Routing Protocols Metrics The Metric Field in the

Routing Table

Metric used for each routing protocol

-RIP - hop count (lowest wins)

-IGRP & EIGRP - Bandwidth (used by default), Delay (used by default), Load, Reliability (lowest wins)

-IS-IS & OSPF – Cost, Bandwidth (Cisco’s implementation) (lowest wins)

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What if multiple paths have same metric? Both are placed in the routing table and packets are

balanced between the 2. To see if it is in effect, just look at the routing table.

Load balancing

This is the ability of a router to distribute packets among multiple same cost paths

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Administrative Distance of a Route Purpose of Administrative Distance

It’s a numeric value that specifies the trustworthiness of a route. Uses AD to select the best path when it learns about the same destination network from 2 or more different routing sources.

Route with lowest AD is the one chosen for the routing table (Best path)

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Administrative Distance of a Route Identifying the Administrative Distance (AD) in a

routing tableIt is the first number in the brackets in the routing table

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Administrative Distance of a Route Dynamic Routing Protocols – the lower the number,

the more trustworthy the route!

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Administrative Distance of a Route Directly connected routes

Have a default AD of 0

Static RoutesAdministrative distance of a static route has a default value of 1

To see the AD of a static route, use the command below:

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Administrative Distance of a Route Directly connected routes

-Immediately appear in the routing table as soon as the interface is configured and the lines are brought up – that is the IP address is assigned to an interface! These routes have an AD of 0.

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Ch. 3…Dynamic Routing Protocols is finished

1.Study Guide – 1. Pg. 139 – Matching2. Pg. 142 –Dynamic Routing Protocols Classification Chart3. Pg. 144-145 – Metric Parameters Exercise4. Pg. 146 – Routing Sources & AD Exercise5. Pg. 146-147 – Identifying Elements of a routing table

2.Labs - Packet Tracer Skills Integration Challenge TODAY!

3.Test on Ch. 3 will be Monday, Feb. 11, 2013 – NO HANDS ON! Just lecture notes.. MC, Tables to fill in, Interpreting the routing table.

4.If you don’t get through with the labs today, you can finish them over the weekend.

5.Online test for Ch. 3 – will be on until Sunday night, Feb. 10, 2013, midnight!