IP routing protocols

325 Pages·2021·20.656 MB·English

by  James Aweya

IP Routing Protocols

IP Routing Protocols
Fundamentals and Distance-Vector Routing
Protocols
James Aweya
First edition published 2021
by CRC Press
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Library of Congress Cataloging-in-Publication Data
Names: Aweya, James, author.
Title: IP routing protocols / James Aweya.
Description: First edition. | Boca Raton : CRC Press, 2021. | Includes bibliographical references
and index. | Contents: v. 1. Fundamentals -- v. 2. Link-state and patth-vector routing protocols. |
Summary: "This two-volume book describes the most common IP routing protocols used today (RIPv2,
EIGRP, OSPFv2, IS-IS, and BGPv4), explaining the underlying concepts of each protocol and how the
protocol components and processes fit within the typical router"-- Provided by publisher.
Identifiers: LCCN 2020052474 (print) | LCCN 2020052475 (ebook) | ISBN 9780367709624 (v. 1 ;
paperback) | ISBN 9780367710415 (v. 1 ; hardback) | ISBN 9780367709631 (v. 2 ; paperback) | ISBN
9780367710361 (v. 2 ; hardback) | ISBN 9781003149040 (v. 1 ; ebook) | ISBN 9781003149019 (v. 2 ;
ebook)
Subjects: LCSH: TCP/IP (Computer network protocol)
Classification: LCC TK5105.585 .A94 2021 (print) | LCC TK5105.585 (ebook) | DDC 004.6/65--dc23
LC record available at https://lccn.loc.gov/2020052474
LC ebook record available at https://lccn.loc.gov/2020052475
ISBN: 978-0-367-71041-5 (hbk)
ISBN: 978-0-367-70962-4 (pbk)
ISBN: 978-1-003-14904-0 (ebk)
Typeset in Times
by SPi Global, India
Contents
Preface ......................................................................................................................xv
Author .....................................................................................................................xxi
Chapter 1 Introduction to IP Routing Protocols ...................................................1
1.1 Why We Need Routing Protocols ..............................................1
1.2 Routing Methods .......................................................................1
1.2.1 Directly Connected Interface ........................................2
1.2.2 Static Routing ...............................................................3
1.2.3 Default Routing ............................................................4
1.2.3.1 Default Route for an IP Host ........................4
1.2.3.2 Default Route in a Router .............................4
1.2.4 Dynamic Routing Protocols .........................................5
1.2.4.1 Routing Updates ...........................................8
1.2.4.2 Periodic versus Triggered Routing
Updates .........................................................8
1.2.4.3 Routing Information Authentication .............9
1.2.4.4 Routing Information and Network
Convergence................................................10
1.3 Autonomous System ................................................................11
1.3.1 What Is a Network Prefix and a Route? .....................11
1.3.2 Autonomous System Numbers (ASNs) ......................12
1.3.3 Multiple Routing Domains in an Autonomous
System ........................................................................13
1.3.4 Types of Autonomous Systems ..................................14
1.4 Routing Metrics and Costs ......................................................15
1.4.1 Hop Count ..................................................................15
1.4.1.1 Network Diameter: Maximum Hop
Count ...........................................................16
1.4.1.2 “Infinity” Hop Count as a Signaling
Mechanism for Network Failures ...............17
1.4.1.3 Limitations of the Hop Count as a
Routing Metric ............................................17
1.4.2 Bandwidth ..................................................................17
1.4.3 Delay ..........................................................................18
1.4.4 Traffic Load ................................................................18
1.4.5 Reliability ...................................................................18
v
vi Contents
1.4.6 Cost .............................................................................19
1.4.6.1 Example: OSPF Cost ..................................19
1.4.6.2 Cost Based on Interface Bandwidth............19
1.5 Classification of Routing Protocols .........................................20
1.5.1 Interior versus Exterior Routing Protocols .................21
1.6 Least-Cost Routing ..................................................................22
Review Questions ...............................................................................24
References ..........................................................................................24
Chapter 2 Types of Dynamic Routing Protocols ................................................25
2.1 Introduction .............................................................................25
2.2 Distance-Vector Routing Protocols .........................................25
2.2.1 Basic Characteristics of Distance-Vector Routing
Protocols .....................................................................25
2.2.2 Distance-Vector Routing Protocol Operations ...........30
2.2.3 What Is a Rooting Loop?............................................31
2.2.4 Routing Loops and Workarounds – Enhancing the
Performance of Distance-Vector Routing
Protocols .....................................................................32
2.2.4.1 Initial Full Routing Table Update and
Periodic Updates .........................................33
2.2.4.2 Route Maintenance and Invalidation
Timers .........................................................34
2.2.4.3 Holddown Timers .......................................36
2.2.4.4 Triggered Updates .......................................38
2.2.4.5 Count-to-Infinity (Maximum Hop
Count) .........................................................39
2.2.4.6 Poison Reverse ............................................41
2.2.4.7 Split Horizon ...............................................42
2.3 Link-State Routing Protocols ..................................................44
2.3.1 OSPF versus IS-IS Metrics .........................................45
2.3.2 Basic Characteristics of Link-State Routing
Protocols .....................................................................46
2.3.3 Link-State Routing Protocol Operations ....................47
2.3.3.1 Neighbor Discovery ....................................48
2.3.3.2 Link-State Flooding ....................................50
2.3.3.3 Link-State Database ....................................51
2.3.3.4 Link-State Routing Process ........................52
2.3.3.5 Calculating the Shortest Paths and
Constructing the Routing Table ..................53
2.3.3.6 Areas ...........................................................56
2.4 Path-Vector Routing Protocols ................................................57
Contents vii
2.4.1 Why an IGP Is Not Recommended for Routing
between Routing Domains or
Autonomous Systems .................................................58
2.4.2 Using an EGP between Routing Domains:
Path-Vector Routing Protocol .....................................60
2.4.3 BGP: A Path-Vector Routing Protocol .......................62
2.4.3.1 Internal and External BGP Peering .............63
2.4.3.2 Basic Characteristics of BGP Routes .........63
2.4.3.3 BGP Autonomous System Path
Advertisement .............................................65
2.4.3.4 Loop-Free Paths within an Autonomous
System .........................................................65
2.4.3.5 Manually Configured BGP Connections
over TCP .....................................................65
2.4.4 BGP and Path Attributes .............................................66
2.5 The IP Routing Table and Selection of Best Paths ..................68
2.5.1 Path Metrics and Routing Protocols ...........................68
2.5.1.1 Equal-Cost Multipath (ECMP)
Routing .......................................................69
2.5.2 Administrative Distance and Route Selection ............69
2.5.2.1 Administrative Distance Use
Case Example .............................................70
2.5.3 Prefix Length and Longest Prefix
Matching Lookup .......................................................71
Review Questions ...............................................................................73
References ..........................................................................................74
Chapter 3 Routing and Forwarding Tables in Routing Devices ..........................77
3.1 Introduction .............................................................................77
3.2 Functional Components of an IP Router .................................77
3.2.1 IP Control Engine (or Route Processor) .....................77
3.2.2 IP Forwarding Engine ................................................79
3.3 High-Level Router Architectures .............................................80
3.3.1 Router Architectures with Centralized
Forwarding Engine .....................................................80
3.3.2 Router Architecture with Multiple
Centralized Forwarding Engines ................................81
3.3.3 Router Architecture with Distributed
Forwarding Engines ...................................................82
3.3.4 Control Plane Redundancy .........................................84
3.4 IP Routing and Forwarding Tables ..........................................85
3.4.1 Routing Table .............................................................85
viii Contents
3.4.1.1 Routing Table Entries .................................85
3.4.1.2 Routing Tables in a Router with Multiple
Protocols .....................................................88
3.4.1.3 Types of Unicast Routing Tables ................90
3.4.1.4 Aggregate or Summary Routes in the
Routing Table ..............................................91
3.4.2 Forwarding Table ........................................................91
3.5 A Note on Layer 2 Adjacency Table ........................................92
3.6 IP Forwarding Operations .......................................................92
3.6.1 Handling Special Addresses During
Packet Forwarding ......................................................94
3.7 Redistributing Routing Information and Routing Metric
Translation ...............................................................................95
3.7.1 The Need for Route Redistribution ............................95
3.7.2 Filtering Inbound and Outbound Routing
Information .................................................................95
3.7.3 The Need for Routing Metric Translation ..................96
Review Questions ...............................................................................97
References ..........................................................................................98
Chapter 4 Static Routes in the Routing Table .....................................................99
4.1 Introduction .............................................................................99
4.2 Benefits of Dynamic Routing Protocols ..................................99
4.3 Benefits of Static Routing ......................................................100
4.4 Configuring Dynamic Routing versus Static Routing ...........103
4.5 Standard Static Route ............................................................104
4.5.1 Concept of Qualified Next Hop ................................105
4.6 Default Static Route...............................................................106
4.7 Summary Static Route ...........................................................108
4.8 Floating Static Route .............................................................111
Review Questions .............................................................................113
References ........................................................................................113
Chapter 5 Routing Information Protocol (RIP) ................................................115
5.1 Introduction ...........................................................................115
5.2 Routing Protocols and Their Databases .................................115
5.3 RIP Overview ........................................................................117
5.4 RIPv2 Message Format and Other Characteristics ................117
5.4.1 RIPv2 Message Format ............................................118
5.4.2 Interpreting the Address Family Identifier (AFI)
Field in RIPv2 ..........................................................119
5.4.3 RIPv2 Routing Table ................................................120
Contents ix
5.4.4 RIPv2 Timers ............................................................120
5.4.5 RIPv2 Request Message ...........................................120
5.4.6 RIPv2 Response Messages .......................................121
5.4.7 Sending and Receiving RIPv2 Request and
Response Messages ..................................................122
5.5 RIPv2 Authentication ............................................................122
5.5.1 Plaintext Authentication ...........................................123
5.5.2 Cryptographic Authentication ..................................124
5.5.2.1 RIPv2 Authentication Message
Generation .................................................126
5.5.2.2 RIPv2 Authentication Message
Reception ..................................................127
5.6 High-Level RIP Router Architecture, Processes, and
Databases ...............................................................................128
5.6.1 The RIP Process .......................................................129
5.6.2 The Management Process .........................................129
5.6.2.1 The Route Store Process ...........................131
5.6.2.2 The Interface Manager ..............................132
5.6.2.3 The Sockets Manager................................134
5.6.2.4 The Redistribution Manager .....................137
5.6.3 The Routing Table Manager Process ........................137
5.7 Filtering Routing Updates in RIP ..........................................140
5.7.1 Configuration of Passive Interface to Prevent or
Restrict Routing Updates .........................................140
5.7.2 Filtering Routes in Incoming and Outgoing
Routing Updates .......................................................141
5.7.2.1 Distribute-list In ........................................141
5.7.2.2 Distribute-list Out .....................................142
5.8 Summary of RIPv2 Features .................................................142
Review Questions .............................................................................144
References ........................................................................................144
Chapter 6 Enhanced Interior Gateway Routing Protocol (EIGRP) ..................147
6.1 Introduction ...........................................................................147
6.2 EIGRP Overview ...................................................................147
6.3 EIGRP Concepts ....................................................................149
6.3.1 Reliable Transport Protocol ......................................149
6.3.2 Main EIGRP Databases ............................................151
6.3.2.1 Neighbor Table..........................................151
6.3.2.2 Topology Table .........................................152
6.3.2.3 Routing Table ............................................153
6.3.2.4 Other EIGRP Concepts .............................154
6.3.3 Neighbor Formation .................................................154