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 a Hypothesis 366
       Gathering Further Information 367
       Proposing and Testing Another Hypothesis 367
       Solving the Problem 368
       Troubleshooting GRE Tunnels 368
   Troubleshooting Branch 3’s Route Summarization 369
       Verifying the Problem and Choosing an Approach 369
       Gathering Information 370
       Analyzing the Information and Proposing a Hypothesis 373
       Testing the Hypothesis and Solving the Problem 373
       OSPF Summarization Tips and Commands 374
   Troubleshooting AAA Authentication on the Branch 1 Router 375
       Verifying the Problem and Choosing an Approach 375
       Gathering Information 375
       Proposing a Hypothesis 376
       Testing the Hypothesis and Solving the Problem 376
       Troubleshooting AAA 377
Bank of POLONA Trouble Ticket 4 378
   Troubleshooting PC0’s Connectivity to IPv6 Internet 378
       Verifying the Problem and Choosing an Approach 378
       Gathering Information 379
       Analyzing the Information and Proposing and Testing a Hypothesis 381
       Gathering Further Information 382
       Analyzing Information and Proposing and Testing Another Hypothesis 383
       Solving the Problem 384
       Troubleshooting OSPF for IPv6 385
   Troubleshooting the Dysfunctional Totally Stubby Branch Areas 386
       Verifying the Problem and Choosing an Approach 386
       Gathering Information 387
       Analyzing Information 389
       Proposing and Testing a Hypothesis 389
       Solving the Problem 390
       OSPF Stub Areas 391
Summary 391
Review Questions 394
Chapter 10 Troubleshooting Case Study: RADULKO Transport 397
RADULKO Transport Trouble Ticket 1 398
   Mitigating Unauthorized Switches Added by Employees 398
       Gathering Information 399
       Analyzing Information 400
       Proposing a Hypothesis and Solving the Problem 400
       Troubleshooting Spanning Tree Protocol 401
   Troubleshooting Policy-Based Routing 403
       Verifying and Defining the Problem 404
       Gathering Information 404
       Analyzing the Information 405
       Proposing and Testing a Hypothesis 405
       Solving the Problem 406
       Troubleshooting PBR 407
   Troubleshooting Neighbor Discovery 407
       Verifying and Defining the Problem 408
       Gathering Information 408
       Proposing and Testing a Hypothesis 409
       Solving the Problem 409
       Troubleshooting CDP and LLDP 410
RADULKO Transport Trouble Ticket 2 411
   Troubleshooting VLANs and PCs Connectivity Problems 411
       Verifying the Problem 412
       Gathering Information 412
       Analyzing the Information 413
       Proposing and Testing a Hypothesis 413
       Solving the Problem 414
   Troubleshooting VTP 415
   Troubleshooting Branch Router’s IPv6 Problems 416
       Verifying the Problem 416
       Gathering Information 417
       Proposing and Testing a Hypothesis 418
       Solving the Problem 418
       Troubleshooting EIGRP for IPv6 419
   Troubleshooting MP-BGP Session Problem 420
       Verifying the Problem 420
       Gathering Information 420
       Analyzing the Information and Proposing a Hypothesis 421
       Solving the Problem 422
       Troubleshooting MP-BGP 423
RADULKO Transport Trouble Ticket 3 424
   Troubleshooting PC1’s Problem Accessing the SRV Server at the Distribution Center 424
       Verifying and Defining the Problem 424
       Gathering Information 425
       Analyzing Information 428
       Proposing and Testing a Hypothesis 428
       Solving the Problem 429
       Troubleshooting the OSPFv3 Address Families Feature 429
   Troubleshooting OSPFv3 Authentication 430
       Verifying the Problem 430
       Gathering Information 431
       Analyzing Information 432
       Proposing and Testing a Hypothesis 432
       Solving the Problem 433
RADULKO Transport Trouble Ticket 4 433
   Troubleshooting Undesired External OSPF Routes in DST’s Routing Table 434
       Verifying and Defining the Problem 434
       Gathering Information 435
       Analyzing Information 436
       Proposing and Testing a Hypothesis 437
       Solving the Problem 439
Troubleshooting PCs IPv6 Internet Access 440
       Verifying the Problem 440
       Gathering Information 440
       Analyzing Information 442
       Proposing and Testing a Hypothesis 443
       Solving the Problem 444
Summary 444
Review Questions 448
Appendix A Answers to Review Questions 451
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