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$ curl repovive.com/roadmaps/network-design/troubleshooting-methodology/layer-2-troubleshooting

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Layer 2 Troubleshooting - Troubleshooting Methodology | Network Design | Repovive

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Network Design26 sections · 911 units44h total

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Layer 2 Troubleshooting

Data link issues

Layer $2$ problems involve MAC addresses, VLANs, and switching. You have physical connectivity but frames are not reaching their destination.

VLAN issues:

Port in wrong VLAN
Native VLAN mismatch on trunks
Trunk not allowing required VLANs

Spanning tree:

Port stuck in blocking state
Unexpected root bridge election

Diagnostic commands:

show mac address-table
show vlan brief
show interfaces trunk
show spanning-tree

Check that MAC addresses appear where expected. Verify VLAN assignments match your design.