TcL Scripting for Cisco IOS

; Arvind Durai ; John Lautmann


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. Les mer
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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.


Ray Blair, CCIE No. 7050, is a Cisco vertical solutions architect specializing in large network designs. He has more than 20 years of experience in designing, implementing, and maintaining networks, and maintains three CCIE certifications.


Arvind Durai, CCIE No. 7016, Advanced Services Technical Leader for Cisco, specializes in supporting major Cisco enterprise customers in finance, manufacturing, e-commerce, government, and healthcare. He holds CCIEs in Routing and Switching, and in Security.


John Lautmann, Cisco Software Engineer, has developed and enhanced network management software for twelve years, and holds six patents. He has helped develop new Cisco IOS features ranging from data link switching to IOS Tcl Interpeter and digitally signed Tcl scripts.


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.


Category: Networking

Covers: Network Administration

$60.00 USA / $72.00 CAN





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 110

    References 110

Chapter 5 Advanced Tcl Operation in Cisco IOS 111

    Introduction to the Syslog Protocol 112

    Configuring Syslog Server Parameters in Cisco IOS 113

    Syslog Tcl Script Example 116

        Syslog Tcl Script Sample Output 118

    Sending Syslog Messages to a File 121

        Syslog Server Script Procedures 124

        Syslog Server Script Body 127

    Putting the Syslog Script into Operation 129

    Introduction to Embedded Syslog Manager 130

        Filtering Syslog Messages 130

        ESM Global Variables 134

        Rebuilding a Syslog Message from Its Components 136

        Displaying/Adding ESM Tcl Script Filters 137

    Introduction to Embedded Menu Manager 139

    Using Tcl as a Web Server 144

        Obtaining a Free Web Server Application 147

        Reverse Engineering the Web Server 149

        Creating Your Own Simple Web Page 152

        Creating a Web Page Using IOS show Commands 154

        Adding User Input to the Web Page 157

    Introduction to IP SLA 160

        Adding the IP SLA Measurement to the Web Page 162

        Modifying the Button and Label for User Input 162

        Creating a Tcl Script to Display IP SLA Measurement Results 163

        Putting the New Tcl Scripts into Operation 165

        Reformatting the IP SLA Output for Readability 167

        Automatic Removal and Creation of IP SLA Entries 170

        Displaying the Results of the IP SLA Measurement with Auto-Refresh 174

    Tcl Script Refresh Policy 177

    SNMP Proxy Event Detector 178

    Remote-Procedure Call Requests 179

    Multiple-Event Support for Event Correlation 180

    Using the clear Command 181

    Summary 182

    References 182

Chapter 6 Tcl Script Examples 183

    Creating an Application from Start to Finish 183

        Determine What You Want to Accomplish 183

        Creating a Flowchart 184

        Deciding What the User Interface Should Look Like 185

        Write the Code in Pseudo-Code 187

        Before You Begin 188

        Starting to Program the Application 190

        Configuring the Web Server 190

        Writing Code for the MPLS VPN Script 191

        Configuring HTML 209

        Writing Code for the MPLS CFG Script 216

        Troubleshooting as You Go 228

    Using Tcl to Troubleshoot Network Problems 230

        Monitoring the Console for Events 233

    Creating a Web Application for Remote SNMP Graphing 236

    Summary 241

    References 241

Chapter 7 Security in Tcl Scripts 243

    Introduction to PKI Infrastructure 243

        PKI Prerequisite 244

        Confidentiality with PKI 244

        Digital Signatures with PKI 245

    Using Digital Signatures to Sign a Tcl Script 247

        Step 1: Decide on the Final Tcl Script Contents (Myscript) 248

        Step 2: Generate a Public/Private Key Pair 248

        Step 3: Generate a Certificate with the Key Pair 250

        Step 4: Generate a Detached S/MIME pkcs7 Signature for Myscript Using the Private Key 250

        Step 5: Modify the Format of the Signature to Match the Cisco Style for Signed Tcl Scripts and Append

    It to the End of Myscript 251

    Tcl Script-Failure Scenario 256

    Scaling Tcl Script Distribution 257

    Summary 258

    References 258

Appendix A Cisco IOS Tcl Commands Quick Reference 259

TOC, 9781587059452, 5/17/10


Om forfatteren

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.