1© 2003, Cisco Systems, Inc. All rights reserved.

Computer Networks 6 Layer 2 troubleshooting

Halmstad University Olga Torstensson

035-167575 olga.torstensson@ide.hh.se

222© 2003, Cisco Systems, Inc. All rights reserved.

Module 4 Troubleshooting Layer 2

• Data Link Layer Problems• LAN Switching• Frame Relay• ISDN• PPP

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Symptoms of Data Link Layer Problems

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High Layer Protocol Failure

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PING to find Boundary of Problem

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Examine Line Status

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Suboptimal Traffic Flow

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Intermittent Packet Loss

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Interface Encapsulation

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Troubleshooting LAN Switching

ReviewReview theory :STP VTPtheory :STP VTP

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• Don’t configure VTP servers off-line – VTP advertisement revision may cause problems in the domain

• vtp - domain, mode, passwordshow vlan, show vtp domain, show vtp statistics

show vtp status, show vtp counters

Troubleshooting VTP

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Show vtp status

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Characteristics of STP Failure & Switching Loops

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STP

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Show spanning-tree

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Troubleshooting LAN Switching

show vlanshow vlan, , show spanning-treeshow spanning-tree, ,

debug vlan packetdebug vlan packet

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Misconfigured EtherChannel