Transcript CCNA 1 Module 11 TCP/IP Transport and Application Layers

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 multipath 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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Typical Layer 1 Errors
• 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
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Typical Layer 2 Errors
• Improperly configured serial
interfaces
• Improperly configured
Ethernet interfaces
• Improper encapsulation set
• Improper clock rate settings
on serial interfaces
• Network interface card (NIC)
problems
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Typical Layer 3 Errors
• Routing protocol not enabled
• Wrong routing protocol
enabled
• Incorrect IP addresses
• Incorrect subnet masks
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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
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