chapter 09 - net testing
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NETWORK TESTING &NETWORK TESTING &
TROUBLESHOOTING TROUBLESHOOTING
TS, PHẠM VĂN TÍNHTS, PHẠM VĂN TÍNH
PART15PART15
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The show ip route CommandThe show ip route Command
The show ip route command displays the contents of the IP routing table. This table contains entries for all known networks and subnetworks, and a code that indicates how that information was learned.
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Determining the Gateway of Last ResortDetermining the Gateway of Last Resort
The term “gateway of last resort” includes the default route, default network, and default gateway.
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Determining Administrative DistanceDetermining Administrative Distance
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Determining the route metricDetermining the route metric
Routing protocols use metrics to determine the best route to a destination.
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Typical Layer 1 ErrorsTypical Layer 1 Errors
Broken cables Disconnected cables Cables connected to the wrong
ports Intermittent cable connection Wrong cables used for the task at
hand (must use rollovers, crossover cables, and straight-through cables correctly)
Transceiver problems DCE cable problems DTE cable problems Devices turned of
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Typical Layer 2 ErrorsTypical Layer 2 Errors
Improperly configured serial interfaces
Improperly configured Ethernet interfaces
Improper encapsulation set (HDLC is default for serial interfaces)
Improper clockrate settings on serial interfaces
Network interface card (NIC) problems
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Typical Layer 3 ErrorsTypical Layer 3 Errors
Routing protocol not enabled
Wrong routing protocol enabled
Incorrect IP addresses
Incorrect subnet masks
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Troubleshooting Layer 1 using show Troubleshooting Layer 1 using show interfacesinterfaces
An increasing number of carrier transitions counts on a serial link may indicate one or more of the following problems: – Line interruptions due to problems in the service
provider network. – Faulty switch, DSU, or router hardware.
The following Layer 1 problems could be a cause of interface resets:– Bad line causing carrier transitions – Possible hardware problem at the CSU, DSU, or
switch If carrier transitions and interface resets are
increasing or if input errors are high while interface resets are increasing, the problem is likely to be a bad link or defective CSU or DSU.
Show
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Troubleshooting Layer 2 using show Troubleshooting Layer 2 using show interfacesinterfaces
If the interface is up and the line protocol is down, a Layer 2 problem exists. Among the possible causes are:
No keepalives
No clock rate
Mismatch in encapsulation type
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Troubleshooting routing issuesTroubleshooting routing issues
• Show ip route
• Show ip protocols
Show IP ROUTE & PROTOCOLS
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