A guide to building and modifying Tcl scripts to automate network administration tasks

Streamline Cisco network administration and save time with Tcl scripting

Cisco networking professionals are under relentless pressure to accomplish more, faster, and with fewer resources. The best way to meet this challenge is to automate mundane or repetitive tasks wherever possible. In this book, three Cisco experts show you how to use Tcl scripting for Cisco IOS devices to do just that.

You'll learn easy techniques for creating, using, and modifying Tcl scripts that run directly on Cisco network devices from the Cisco IOS command line. The authors first teach basic Tcl commands and concepts for capturing and manipulating data and for querying or controlling Cisco equipment. Building on these core skills, they show you how to write scripts that automate and streamline many common IOS configuration, monitoring, and problem-solving tasks.

The authors walk through the entire script development process, including planning and flowcharting what you want to accomplish, formatting your code, adding comments, and troubleshooting script errors. They also present many downloadable sample scripts, along with practical guidance for adapting them to your own environment.

Whatever your role in managing, monitoring, or securing Cisco IOS networks and equipment, this book will help you get the job done more rapidly and efficiently.

• Automate routine administration tasks you've always performed manually
• Instantly collect and modify IOS router configurations and other data
• Write Syslog scripts to document failures, monitor network health, collect statistics, and send alarm messages
• Implement automated network performance measurement using IP SLA
• Use the Embedded Event Manager's event detectors, server, and policies to customize device operation
• Trigger preplanned actions to correct problems as they arise
• Simplify policy management using the Tcl script refresh feature
• Protect Tcl script security with digital signatures and PKI
• Understand how Tcl functions within the Cisco IOS environment
• Master Tcl syntax and commands through hands-on practice
• Learn best scripting practices through expert examples
• Quickly modify this book's examples for your own environment

This book is part of the Networking Technology Series from Cisco Press®, which offers networking professionals valuable information for constructing efficient networks, understanding new technologies, and building successful careers.

Ray Blair, CCIE No. 7050, is a Vertical Solutions Architect and has been with Cisco Systems for more than 10 years, working primarily with large network designs. He has almost 22 years of experience with designing, implementing, and maintaining networks that have included nearly all networking technologies. During the early stages of his career, he wrote many applications using Assembly language and C. Mr. Blair maintains three CCIE certifications in Routing and Switching, Security, and Service Provider. He is also a Certified Information Systems Security Professional (CISSP) and coauthor of the Cisco Secure Firewall Services Module book.

Arvind Durai , CCIE No. 7016, is an Advanced Services Technical Leader for Cisco Systems. His primary responsibility in the past 10 years has been in supporting major Cisco customers in the enterprise sector, including financial, manufacturing, e-commerce, state government, utility (smart grid networks) and health-care sectors. Some of his focuses have been on security, multicast, network virtualization, and he has authored several white papers and design guides in various technologies. He has leveraged Embedded Event Manager (EEM) and Tool Command Language (Tcl) scripts in various customer designs. Mr. Durai maintains two CCIE certifications: Routing and Switching, and Security. He holds a Bachelor of Science degree in electronics and communication, a master's degree in electrical engineering (MS), and master's degree in business administration (MBA), and is a coauthor of Cisco Secure Firewall Services Module.

John Lautmannis a Software Engineer for Cisco Systems. He has developed and enhanced network management software for nearly 14 years. Before joining Cisco, he held positions in customer support and software testing. With six networking patents, John has been involved in the development of new Cisco IOS features such as data-link switching, syslog, configuration rollback and archiving, IOS Tcl interpreter, digitally signed Tcl scripts, and Multiprotocol Label Switching (MPLS) ping and trace. Mr. Lautmann holds a Bachelor of Science degree in computer science and master's degrees in both business and engineering.

Introduction xiv

Chapter 1 The Origin of Tcl 1

Tcl and Cisco IOS Software 3

Embedded Event Manager and Tcl 4

Restriction of Tcl in IOS 4

Tcl with EEM Support in IOS 5

Using Tcl Scripts in the Network 8

Troubleshooting Problems 8

Monitoring the Network 8

Adding Intelligence to Cisco IOS Protocols 9

Summary 9

References 9

Chapter 2 Tcl Interpreter and Language Basics 11

Simple Variables in Tcl 12

Storing Variables 12

Viewing Variables 13

The append Command 13

The incr Command 13

Representation of Variables in Tcl 14

Command Substitution 14

Variable Substitution 15

Lists 17

lappend 18

lindex 18

linsert 18

llength 19

lsearch 19

lreplace 20

lrange 20

lsort 20

Procedures 21

for Command 22

foreach Command 23

while Command 23

Arrays 24

if Command 26

switch Command 27

Files 28

Summary 31

References 31

Chapter 3 Tcl Functioning in Cisco IOS 33

Understanding the Tcl Interpreter in Cisco IOS 33

Using Cisco IOS Exec-Mode Parser in the Tcl Shell 34

Entering an IOS Command into the Tcl Command Interpreter 35

Using Tcl to Enter Commands 36

Copying a Tcl Script to a Cisco IOS Device 38

Fetching a Cisco IOS Tcl Script from a Remote Device 41

Using Tcl to Examine the Cisco IOS Device Configuration 41

Using Tcl to Modify the Router Configuration 43

Using Tcl with SNMP to Check MIB Variables 44

Other Uses of SNMP 44

Enabling SNMP on a Cisco IOS Device 47

Querying the Configuration of a Cisco IOS Device Using SNMP 48

Modifying the Configuration of a Cisco IOS Device Using SNMP 51

Summary 53

References 53

Chapter 4 Embedded Event Manager (EEM) 55

EEM Architecture 55

Policies 56

EEM Server 56

Event Detectors 57

Software Release Support for EEM 60

Platform and IOS Considerations for EEM 65

Writing an EEM Applet 66

Practical Example of an Event Trigger 68

Using Object Tracking as an Event Trigger 69

Creating Applet Actions 70

Examples of EEM Applets 70

Configuring the IP SLA Sender and Responder 72

Applet and IP SLA Route Failover Example 74

Applet That Monitors the Default Route 83

Applet and Application Failover with a Network Address Translation Example 88

Using EEM and Tcl Scripts 96

Programming Policies with Tcl 97

Tcl Example Used to Check for Interface Errors 98

Tcl Example Used to Check the CPU Utilization 104

Summary …