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1© 2003, Cisco Systems, Inc. All rights reserved.
CCNA 2 v3.0 Module 9 Basic Router Troubleshooting
444© 2003, Cisco Systems, Inc. All rights reserved.
Objectives
• Examining the routing table
• Network testing
• Troubleshooting router issues
555© 2003, Cisco Systems, Inc. All rights reserved.
Examining the routing table
666© 2003, Cisco Systems, Inc. All rights reserved.
The show ip route Command
The show ip route command displays the contents of the IP routing table.
777© 2003, Cisco Systems, Inc. All rights reserved.
Static Routing
888© 2003, Cisco Systems, Inc. All rights reserved.
Dynamic Routing
999© 2003, Cisco Systems, Inc. All rights reserved.
Default Route
101010© 2003, Cisco Systems, Inc. All rights reserved.
Configuring a Default Route
• The ip default-network command establishes a default route in networks using dynamic routing protocols.
Router(config-router)#ip default-network network-number
• Creating an ip route to 0.0.0.0/0 is another way to configure a default route.
Router(config)#ip route 0.0.0.0 0.0.0.0 [next-hop-ip-address | exit-interface]
111111© 2003, Cisco Systems, Inc. All rights reserved.
Determining Route Source and Destination
121212© 2003, Cisco Systems, Inc. All rights reserved.
Determining L2 and L3 Addresses
131313© 2003, Cisco Systems, Inc. All rights reserved.
Determining Administrative Distance
141414© 2003, Cisco Systems, Inc. All rights reserved.
Determining the Route Metric
Routing protocols use metrics to determine the best route to a destination.
151515© 2003, Cisco Systems, Inc. All rights reserved.
Determining the Route Next Hop
• Destination/next hop associations tell a router that a particular destination can be reached optimally by sending the packet to a particular router.
161616© 2003, Cisco Systems, Inc. All rights reserved.
Determining the Last Routing Update
• Use the following commands to find the last routing update:
show ip route
show ip route network
show ip protocols
show ip rip database
171717© 2003, Cisco Systems, Inc. All rights reserved.
Observing Multiple Paths to a Destination
• Some routing protocols support multiple paths to the same destination.
• Unlike single path algorithms, these multi-path algorithms permit traffic over multiple lines, provide better throughput, and are more reliable.
181818© 2003, Cisco Systems, Inc. All rights reserved.
Network testing
191919© 2003, Cisco Systems, Inc. All rights reserved.
Introduction to Network Testing
202020© 2003, Cisco Systems, Inc. All rights reserved.
Structured Approach to Troubleshooting
212121© 2003, Cisco Systems, Inc. All rights reserved.
• Broken cables • Disconnected cables • Cables connected to the wrong ports • Intermittent cable connection • Wrong cables used for the task at
hand • Transceiver problems • DCE cable problems • DTE cable problems • Devices turned off
Typical Layer 1 Errors
222222© 2003, Cisco Systems, Inc. All rights reserved.
• Improperly configured serial interfaces
• Improperly configured Ethernet interfaces
• Improper encapsulation set • Improper clock rate settings
on serial interfaces • Network interface card (NIC)
problems
Typical Layer 2 Errors
232323© 2003, Cisco Systems, Inc. All rights reserved.
• Routing protocol not enabled
• Wrong routing protocol enabled
• Incorrect IP addresses
• Incorrect subnet masks
Typical Layer 3 Errors
252525© 2003, Cisco Systems, Inc. All rights reserved.
Layer 3 Troubleshooting Using Ping
262626© 2003, Cisco Systems, Inc. All rights reserved.
Layer 7 Troubleshooting Using Telnet
272727© 2003, Cisco Systems, Inc. All rights reserved.
Troubleshooting router issues
282828© 2003, Cisco Systems, Inc. All rights reserved.
Troubleshooting Layer 1 Using show interfaces Command
The show interfaces serial command
292929© 2003, Cisco Systems, Inc. All rights reserved.
Troubleshooting Layer 2 Using show interfaces Command
303030© 2003, Cisco Systems, Inc. All rights reserved.
Troubleshooting Using show cdp neighbors Command
313131© 2003, Cisco Systems, Inc. All rights reserved.
Troubleshooting Using show cdp neighbors detail Command
323232© 2003, Cisco Systems, Inc. All rights reserved.
Troubleshooting Using traceroute Command
333333© 2003, Cisco Systems, Inc. All rights reserved.
Troubleshooting Routing Issues
The show ip route Command
343434© 2003, Cisco Systems, Inc. All rights reserved.
Troubleshooting Routing Issues
The show ip protocols Command
353535© 2003, Cisco Systems, Inc. All rights reserved.
Troubleshooting Using show controllers serial Command
The show controllers serial Command
363636© 2003, Cisco Systems, Inc. All rights reserved.
Introduction to debug
Debug syntax