© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
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Chapter 1 1
Introduction to Dynamic
Routing Protocol
Routing Protocols and
Concepts – Chapter 3
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Chapter 1 2© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
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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Chapter 1 3© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
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
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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
 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)
-Exterior Gateway Protocols (EGP)
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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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Chapter 1 10© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
Classifying Routing Protocols
 IGP: Comparison of Distance Vector & Link State
Routing Protocols
Distance vector
– routes are advertised as vectors
of distance & direction.
– incomplete view of network
topology.
–Generally, periodic
updates.
Link state
– complete view of network
topology is created.
– updates are not
periodic.
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Classifying Routing Protocols
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Classifying Routing Protocols
 Classful routing
protocols
Do NOT send subnet mask
in routing updates
 Classless routing
protocols
Do send subnet mask in
routing updates.
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Classifying Routing Protocols
 Convergence is defined as when all routers’ routing
tables are at a state of consistency
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Routing Protocols Metrics
 Metric
A value used by a routing protocol to determine which
routes are better than others.
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Routing Protocols Metrics
 Metrics used in IP routing protocols
-Bandwidth
-Cost
-Delay
-Hop count
-Load
-Reliability
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Routing Protocols Metrics
 The Metric Field in the
Routing Table
 Metric used for each
routing protocol
-RIP - hop count
-IGRP & EIGRP Bandwidth
(used by
default), Delay (used by
default), Load, Reliability
-IS-IS & OSPF – Cost,
Bandwidth (Cisco’s
implementation)
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Routing Protocols Metrics
 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 a metric
It’s a calculated value used to determine the best path to a
destination
 Purpose of Administrative Distance
It’s a numeric value that specifies the preference of a particular
route
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Administrative Distance of a Route
 Identifying the Administrative Distance (AD) in a
routing table
It is the first number in the brackets in the routing table
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Administrative Distance of a Route
 Dynamic Routing Protocols
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Administrative Distance of a Route
 Directly connected routes
Have a default AD of 0
 Static Routes
Administrative distance of a static route has a default value of
1
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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
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Summary
 Dynamic routing protocols fulfill the following functions
-Dynamically share information between routers
-Automatically update routing table when topology changes
-Determine best path to a destination
 Routing protocols are grouped as either
-Interior gateway protocols (IGP)Or
-Exterior gateway protocols(EGP)
 Types of IGPs include
-Classless routing protocols - these protocols include subnet mask
in routing updates
-Classful routing protocols - these protocols do not include subnet
mask in routing update
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Chapter 1 24© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
Summary
 Metrics are used by dynamic routing protocols to calculate the
best path to a destination.
 Administrative distance is an integer value that is used to
indicate a router’s “trustworthiness”
 Components of a routing table include:
-Route source
-Administrative distance
-Metric
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