Chapter 1 Troubleshooting Methods 1
Troubleshooting Principles 1
Structured Troubleshooting Approaches 4
The Top-Down Troubleshooting Approach 6
The Bottom-Up Troubleshooting Approach 7
The Divide-and-Conquer Troubleshooting Approach 8
The Follow-the-Path Troubleshooting Approach 9
The Compare-Configurations Troubleshooting Approach 10
The Swap-Components Troubleshooting Approach 11
Troubleshooting Example Using Six Different Approaches 12
Summary 13
Review Questions 14
Chapter 2 Structured Troubleshooting 15
Troubleshooting Method and Procedure 16
Defining the Problem 17
Gathering Information 18
Analyzing the Information 20
Eliminating Potential Causes 21
Proposing a Hypothesis (Likely Cause of the Problem) 21
Testing and Verifying Validity of the Proposed Hypothesis 23
Solving the Problem and Documenting the Work 24
Troubleshooting Example Based on the Structured Method and Procedures 25
Summary 26
Review Questions 27
Chapter 3 Network Maintenance Tasks and Best Practices 29
Structured Network Maintenance 29
Network Maintenance Processes and Procedures 31
Common Maintenance Tasks 32
Network Maintenance Planning 33
Scheduling Maintenance 33
Formalizing Change-Control Procedures 34
Establishing Network Documentation Procedures 34
Establishing Effective Communication 35
Defining Templates/Procedures/Conventions (Standardization) 36
Planning for Disaster Recovery 36
Network Maintenance Services and Tools 37
Network Time Services 39
Logging Services 40
Performing Backup and Restore 42
Integrating Troubleshooting into the Network Maintenance Process 47
Network Documentation and Baseline 48
Communication 50
Change Control 53
Summary 54
Review Questions 57
Chapter 4 Basic Switching and Routing Process and Effective IOS Troubleshooting Commands 61
Basic Layer 2 Switching Process 61
Ethernet Frame Forwarding (Layer 2 Data Plane) 62
Layer 2 Switching Verification 67
Basic Layer 3 Routing Process 69
IP Packet Forwarding (Layer 3 Data Plane) 70
Using IOS Commands to Verify IP Packet Forwarding 73
Selective Information Gathering Using IOS show Commands, debug Commands, Ping, and Telnet 76
Filtering and Redirecting show Command's Output 76
Testing Network Connectivity Using Ping and Telnet 81
Collecting Real-Time Information Using Cisco IOS debug Commands 85
Diagnosing Hardware Issues Using Cisco IOS Commands 86
Checking CPU Utilization 87
Checking Memory Utilization 88
Checking Interfaces 89
Summary 92
Review Questions 94
Chapter 5 Using Specialized Maintenance and Troubleshooting Tools 99
Categories of Troubleshooting Tools 100
Traffic-Capturing Features and Tools 101
SPAN 102
RSPAN 103
Information Gathering with SNMP 105
Information Gathering with NetFlow 107
Network Event Notification 109
Summary 113
Review Questions 114
Chapter 6 Troubleshooting Case Study: SECHNIK Networking 117
SECHNIK Networking Trouble Ticket 1 118
Troubleshooting PC1's Connectivity Problem 118
Gathering Information 119
Analyzing Information, Eliminating Causes, and Gathering Further Information 119
Proposing Hypotheses 121
Testing the Hypotheses and Solving the Problem 121
Troubleshooting Ethernet Trunks 122
Troubleshooting PC2's Connectivity Problem 123
Gathering Information 124
Proposing a Hypothesis, Testing the Hypothesis, and Solving the Problem 126
Troubleshooting NAT 127
Troubleshooting PC3's Connectivity Problem 128
Gathering Information 129
Eliminating Possibilities, Proposing a Hypothesis, and Testing the Hypothesis 129
Troubleshooting Network Device Interfaces 130
Troubleshooting PC4's IPv6 Connectivity Problem 131
Gathering Information 131
Eliminating Possibilities, Proposing a Hypothesis, and Testing the Hypothesis 132
Troubleshooting IPv6 Address Assignment on Clients 133
SECHNIK Networking Trouble Ticket 2 134
Troubleshooting PC1's Internet Connectivity Problem 134
Gathering Information 135
Proposing a Hypothesis, Testing the Hypothesis, and Solving the Problem 137
Troubleshooting Network Layer Connectivity 138
Troubleshooting PC2's SSH Connectivity Problem 141
Verifying and Defining the Problem 141
Gathering Information 142
Proposing a Hypothesis and Testing the Hypothesis 143
TCP Three-Way Handshake 145
Troubleshooting PC4's DHCP Address Problem 146
Verifying and Defining the Problem 146
Gathering Information 147
Proposing a Hypothesis, Testing a Hypothesis, and Solving the Problem 148
Troubleshooting Error-Disabled Ports 151
SECHNIK Networking Trouble Ticket 3 152
Troubleshooting PC1 and PC2's Internet Connectivity Issues 153
Verifying and Defining the Problem 153
Gathering Information 153
Proposing a Hypothesis and Testing the Hypothesis 157
Solving the Problem 159
Troubleshooting DHCP 160
The passive-interface Command 161
Troubleshooting PC3's Internet Connectivity Issues 162
Verifying and Defining the Problem 162
Gathering Information 162
Proposing a Hypothesis and Testing the Hypothesis 164
Solving the Problem 165
IPv6 Review 166
Summary 166
Review Questions 169
Chapter 7 Troubleshooting Case Study: TINC Garbage Disposal 173
TINC Garbage Disposal Trouble Ticket 1 174
Troubleshooting Lack of Backup Internet Connectivity Through GW2 174
Information Gathering 176
Analyzing Information, Eliminating Possibilities, and Proposing a Hypothesis 178
Proposing a Hypothesis, Testing the Hypothesis, and Solving the Problem 178
Troubleshooting BGP Neighbor Relationships 181
Troubleshooting PC1's Connectivity Problem 182
Gathering Information 182
Analyzing Information and Gathering Further Information 183
Proposing a Hypothesis, Testing the Hypothesis, and Solving the Problem 184
Troubleshooting Port Security 186
Troubleshooting PC2's Connectivity Problem 187
Gathering Information 188
Eliminating Possibilities, Proposing a Hypothesis, and Testing the Hypothesis 190
Solving the Problem 191
Troubleshooting VLANs 192
TINC Garbage Disposal Trouble Ticket 2 193
Troubleshooting GW1's OSPF Neighbor Relation Problem with Router R1 194
Verifying the Problem 194
Gathering Information 194
Analyzing Information, Eliminating Possibilities, and Proposing a Hypothesis 199
Testing the Hypothesis and Solving the Problem 199
Troubleshooting OSPF Adjacency 201
Troubleshooting Secure Shell Version 2 Access to Router R2 from PC4 202
Verifying the Problem 202
Gathering Information 203
Proposing a Hypothesis and Testing the Hypothesis 204
Solving the Problem 205
Troubleshooting SSH and Telnet 206
Troubleshooting Duplicate Address Problem Discovered Through R1 and R2's Log Messages 207
Verifying the Problem 207
Gathering Information 207
Analyzing the Information and Proposing a Hypothesis 210
Testing the Hypothesis and Solving the Problem 210
Troubleshooting HSRP 211
TINC Garbage Disposal Trouble Ticket 3 212
Troubleshooting Sporadic Internet Connectivity Problem Experienced by Users of PC1 and PC2 212
Verifying and Defining the Problem 213
Gathering Information 213
Analyzing Information and Proposing a Hypothesis 215
Testing the Hypothesis and Solving the Problem 217
Troubleshooting Erroneous Routing Information 218
Troubleshooting Multiple Masters within a VRRP 220
Verifying and Defining the Problem 220
Gathering Information 221
Analyzing the Information and Proposing a Hypothesis 222
Testing the Hypothesis, and Solving the Problem 222
Troubleshooting VRRP 224
Troubleshooting EtherChannel Between ASW4 and ASW3 224
Verifying the Problem 224
Defining the Problem 225
Gathering Information 225
Proposing a Hypothesis and Testing the Hypothesis 227
Solving the Problem 228
Troubleshooting EtherChannel 229
TINC Garbage Disposal Trouble Ticket 4 231
Troubleshooting Inconsistent and Sporadic Internet Connectivity Problem Experienced By Users of PC1 and PC2 231
Verifying and Defining the Problem 232
Gathering Information 233
Analyzing Information and Proposing a Hypothesis 235
Testing the Hypotheses 235
Solving the Problem 239
Troubleshooting FHRPs 241
Troubleshooting Sporadic Loss of Connectivity on PC4 242
Verifying the Problem and Making a Troubleshooting Plan 242
Gathering Information 242
Analyzing the Information and Gathering Further Information 244
Proposing a Hypothesis and Testing the Hypothesis 245
Solving the Problem 246
The Cisco IOS DHCP Snooping Feature 248
Cisco Technical Assistance Center 248
Troubleshooting SSH Connection from PC4 to Router GW2 249
Verifying the Problem and Making a Troubleshooting Plan 249
Gathering Information 250
Proposing a Hypothesis and Testing the Hypothesis 251
Solving the Problem 252
Summary 252
Review Questions 255
Chapter 8 Troubleshooting Case Study: PILE Forensic Accounting 257
PILE Forensic Accounting Trouble Ticket 1 258
Troubleshooting PILE's Branch Connectivity to HQ and the Internet 258
Verifying and Defining the Problem 258
Gathering Information 260
Analyzing Information 264
Proposing a Hypothesis and Testing the Hypothesis 264
Solving the Problem 265
Troubleshooting EIGRP Adjacency 266
Troubleshooting PILE's Secondary Internet Connection Through ISP2 267
Verifying and Defining the Problem 267
Gathering Information 268
Analyzing Information and Proposing a Hypothesis 270
Testing the Hypothesis 271
Solving the Problem 273
PILE Forensic Accounting Trouble Ticket 2 274
Troubleshooting Telnet Problem: From PC3 to BR 274
Gathering Information 275
Troubleshooting PILE Network's Internet Access Problem 275
Verifying and Defining the Problem 276
Gathering Information 276
Analyzing Information, Eliminating Causes, and Gathering Further Information 278
Proposing and Testing a Hypothesis 280
Solving the Problem 281
Troubleshooting BGP 281
Troubleshooting PILE Network's NTP Problem 282
Verifying the Problem 283
Gathering Information 283
Analyzing the Gathered Information and Gathering Further Information 284
Proposing a Hypothesis and Testing the Hypothesis 285
Solving the Problem 286
Troubleshooting NTP 286
PILE Forensic Accounting Trouble Ticket 3 287
Troubleshooting PC3's Lack of Internet Connectivity After the Disaster Recovery 287
Verifying the Problem 288
Gathering Information (First Run) 288
Analyzing Information, Proposing, and Testing the First Hypothesis 289
Proposing and Testing the Second Hypothesis 290
Gathering Further Information (Second Run) 292
Proposing and Testing the Third Hypothesis 293
Solving the Problem 294
Disaster Recovery Best Practices 294
Troubleshooting Inter-VLAN Routing 296
Troubleshooting PC4's Problem Accessing Cisco.com 297
Verify the Problem and Select an Approach 297
Gather Information and Analyze the Information 298
Proposing and Testing a Hypothesis 299
Solve the Problem 299
Troubleshooting DNS 300
Remote Device Management Notes 301
PILE Forensic Accounting Trouble Ticket 4 302
Troubleshooting Branch Site Internet Connectivity Problem After EIGRP Reconfiguration 302
Verifying the Problem 302
Gathering Information 303
Gathering Further Information and Analyzing Information 303
Proposing a Hypothesis and Testing the Hypothesis 305
Solving the Problem 307
The EIGRP Stub Configuration 308
The New EIGRP Named Configuration 309
Troubleshooting Management Access to ASW2 310
Verifying the Problem 310
Gathering Information 310
Proposing a Hypothesis and Testing the Hypothesis 311
Solving the Problem 312
Providing a Default Route on Layer 2 And Multilayer Devices 313
PILE Forensic Accounting Trouble Ticket 5 313
Troubleshooting the Redundant Internet Access Path Through the New HQ0 Edge Router 314
Verifying and Defining the Problem 314
Gathering Information 315
Proposing a Hypothesis and Testing the Hypothesis 318
Solving the Problem 319
Troubleshooting BGP Route Selection 321
Troubleshooting Unauthorized Telnet Access 322
Verifying the Problem 322
Gathering Information 322
Gathering Further Information and Analysis Information 323
Proposing a Hypothesis and Testing the Hypothesis 324
Solving the Problem 325
Securing the Management Plane 325
Summary 326
Review Questions 329
Chapter 9 Troubleshooting Case Study: Bank of POLONA 333
Bank of POLONA Trouble Ticket 1 334
Troubleshooting PC3's Lack of Connectivity to SRV2 335
Verifying the Problem 335
Gathering Information 336
Analyzing Information and Proposing a Hypothesis, and Testing the Hypothesis 338
Solving the Problem 339
Troubleshooting Redistribution 339
Troubleshooting VRRP with Interface Tracking 340
Verifying the Problem 340
Gathering Information 341
Analyzing the Information 342
Proposing and Testing a Hypothesis 342
Solving the Problem 343
FHRP Tracking Options 344
Troubleshooting IP SLA Test Not Starting 345
Verifying the Problem 345
Gathering Information 346
Proposing and Testing a Hypothesis 347
Solving the Problem 348
Troubleshooting IP SLA 349
Bank of POLONA Trouble Ticket 2 349
Troubleshooting Summarization Problem on BR3 350
Verifying the Problem 350
Gathering Information 350
Analyzing Information 351
Proposing and Testing a Hypothesis 351
Solving the Problem 352
Troubleshooting EIGRP Summarization 353
Troubleshooting PC0's IPv6 Internet Connectivity 353
Verifying the Problem 353
Gathering Information 354
Analyzing Information 356
Proposing and Testing a Hypothesis 356
Solving the Problem 357
Troubleshooting RIPng 357
Troubleshooting Branch 3's IPv6 Internet Connectivity 358
Verifying the Problem 358
Gathering Information 359
Analyzing Information 361
Proposing and Testing a Hypothesis 361
Solving the Problem 362
Troubleshooting Access Control Lists 362
Bank of POLONA Trouble Ticket 3 364
Troubleshooting Branch 1's IP Connectivity to the Headquarters 364
Verifying the Problem 364
Gathering Information 365
Proposing and Testing
