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CCNA 2 v3.0 Module 9 Basic Router Troubleshooting

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Objectives

• Examining the routing table

• Network testing

• Troubleshooting router issues

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Examining the routing table

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The show ip route Command

The show ip route command displays the contents of the IP routing table.

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Static Routing

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Dynamic Routing

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Default Route

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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]

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Determining Route Source and Destination

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Determining L2 and L3 Addresses

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Determining Administrative Distance

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Determining the Route Metric

Routing protocols use metrics to determine the best route to a destination.

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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.

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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

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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.

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Network testing

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Introduction to Network Testing

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Structured Approach to Troubleshooting

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• 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

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• 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

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• Routing protocol not enabled

• Wrong routing protocol enabled

• Incorrect IP addresses

• Incorrect subnet masks

Typical Layer 3 Errors

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Layer 3 Troubleshooting Using Ping

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Layer 7 Troubleshooting Using Telnet

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Troubleshooting router issues

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Troubleshooting Layer 1 Using show interfaces Command

The show interfaces serial command

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Troubleshooting Layer 2 Using show interfaces Command

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Troubleshooting Using show cdp neighbors Command

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Troubleshooting Using show cdp neighbors detail Command

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Troubleshooting Using traceroute Command

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Troubleshooting Routing Issues

The show ip route Command

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Troubleshooting Routing Issues

The show ip protocols Command

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Troubleshooting Using show controllers serial Command

The show controllers serial Command

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Introduction to debug

Debug syntax