Kayla Agan, CCNA, CCAI Seattle Central Comm. Coll., Seattle WA The network is busted! Oh shoot! How you gonna fix it? Who you gonna call? NetworkBusters!

Kayla Agan, CCNA, CCAI Seattle Central Comm. Coll., Seattle WA Troubleshooting! Use a logical, methodical plan for determining what needs to be fixed on the network. Work from Layer 1 (Physical) and climb the OSI model layer-by-layer until you reach the resolution…or Layer 7 (Application)…whichever comes first.

Kayla Agan, CCNA, CCAI Seattle Central Comm. Coll., Seattle WA OSI Model Layer 7ApplicationTelnet, Browsers, Ftp, Layer 6PresentationEncryption, Compression, Data representation & Data syntax Layer 5SessionConversations & dialogs, Managing sessions between applications Layer 4TransportTCP & UDP, Sliding windows, segments, 3-way handshake, Error checking Layer 3NetworkRouters, Path determination, Protocols, Logical addressing Layer 2Data LinkLLC & MAC, MAC addresses, Bridges & switches, error-checking, Network technologies, Encapsulation Layer 1PhysicalBits, Cables, Connectors, hubs & repeaters

Kayla Agan, CCNA, CCAI Seattle Central Comm. Coll., Seattle WA Layer 1 problems can include: Broken cables Disconnected cables Cables connected to the wrong ports Intermittent failures in cables Poorly terminated cables Wrong cables used for wrong task Transceiver problems DCE problem DTE problem Power issues/turned off or not plugged in

Kayla Agan, CCNA, CCAI Seattle Central Comm. Coll., Seattle WA Layer 2 problems can include: Serial interface configuration mistakes Ethernet interface configuration mistakes Wrong clock rate settings on serial interfaces Wrong encapsulation on serial interfaces –HDLC is default Bad NIC

Kayla Agan, CCNA, CCAI Seattle Central Comm. Coll., Seattle WA Layer 3 problems can include: Routing protocol not enabled Wrong routing protocol enabled Incorrect network/IP address Incorrect subnet mask Incorrect interface addresses Incorrect DNS to IP bindings (host table entries) Wrong autonomous system number for IGRP

Kayla Agan, CCNA, CCAI Seattle Central Comm. Coll., Seattle WA OSI Layer Troubleshooting START Layer 1 OK? Layer 2 OK? Layer 3 OK? Layer 4 OK? Layer 5 OK? Layer 6 OK? Layer 7 OK? STOP Fix Layer 1 Fix Layer 2 Fix Layer 3 Fix Layer 4 Fix Layer 5 Fix Layer 6 Fix Layer 7 NO YES

Kayla Agan, CCNA, CCAI Seattle Central Comm. Coll., Seattle WA Troubleshooting logical steps 1.Define the problem. Symptoms? Potential causes? 2.Gather facts Isolate possible causes 3.Consider the possibilities… Narrow focus areas to specific problem to set boundaries 4.Create plan of action Manipulate 1 variable at a time 5.Implement action plan 5.Perform each step carefully 6.Test to see if symptom disappears 6.Observe results 5.Did you resolve problem? If so, you’re done! 7.Repeat process, if needed. 5.Move to next-most likely cause of problem. Return to Step 4 & repeat until solved.

Kayla Agan, CCNA, CCAI Seattle Central Comm. Coll., Seattle WA Troubleshooting commands What can I learn from each of these commands?What can I learn from each of these commands? –PING –TRACE –TELNET –SHOW IP ROUTE –SHOW INTERFACES –SHOW ARP

Kayla Agan, CCNA, CCAI Seattle Central Comm. Coll., Seattle WA Troubleshooting scenario #1 When trying to ping Lab-E from Lab-a, you receive a series of timeout messages Lab-a# ping lab-e Sending 5, 100-byte ICMP Echos to , timeout is 2 seconds: ….. Success rate is 0 percent (0/5) What’s wrong? 1.Define the problem. 2.Symptoms? Potential causes? 3.Consider the possibilities Narrow the focus 4.Create action plan Manipulate 1 variable at a time 5.Implement action plan Perform 1 step at a time & test. Does symptom disappear? 6.Observe results…problem solved? You’re done. 7.Repeat process. If not, go back to Step 4.

Kayla Agan, CCNA, CCAI Seattle Central Comm. Coll., Seattle WA IP Troubleshooting Everyone has their own series of troubleshooting techniques which vary widely from person to person. –Think linear…logical AND –Think lateral…considering events not directly related to problem at hand…but having some possible impact. Consider…networks are like sports cars, investigating 1 problem can lead you to finding 10 more things that need fixing –Focus on the immediate problem at hand. Make note of the other items you’ve discovered that need attention & save those for another day - in the immediate future!

Kayla Agan, CCNA, CCAI Seattle Central Comm. Coll., Seattle WA IP Troubleshooting # 2 Think about… –If several users located in different areas on the network are reporting similar problems at the same time, They are probably reporting elements of the same problem. If the same problem is occurring in multiple parts of the network, you only have to figure out how to fix it one time AND then fix the other instances of it as well. Think about… –Try to duplicate a problem in the lab & troubleshoot it there! Troubleshooting to resolve problems can often temporarily introduce new problems! –If testing involves reconfiguring a device, make a backup before doing anything! Make sure that you can undo the changes!

Kayla Agan, CCNA, CCAI Seattle Central Comm. Coll., Seattle WA IP Troubleshooting # 3 Think about… –Test, Test & test! Use as few tests as possible to define problem Ensure reliability of test results Validate test results –Repeat each test at least twice! Document tests performed & results Think about… –Document changes to network during troubleshooting so it can be restored when done! –Document any workarounds left in place so others know what’s going on & why network had changed!