Figure 2-39 shows the ?¬‚ow for troubleshooting VLANs and trunks.
Figure 2-39 Troubleshooting VLANs
Native VLAN Mismatches
The native VLAN that is con?¬?gured on each end of an IEEE 802.1Q trunk must be the
same. Remember that a switch receiving an untagged frame assigns the frame to the native
VLAN of the trunk. If one end of the trunk is con?¬?gured for native VLAN 1 and the other
Troubleshoot
Physical Layer
Port Connectivity
Issues
Troubleshoot
VLAN and Trunking
Issues
Troubleshoot
VTP
Issues
Troubleshoot
Spanning-Tree
Issues
Do local and
peer native
VLANs match?
Do local and
peer trunk modes
match?
Does each
VLAN correspond
with a unique
IP subnet?
Does
inter-VLAN
traffic have a
functional Layer 3
process?
Troubleshooting Switched Networks 81
end is con?¬?gured for native VLAN 2, a frame sent from VLAN 1 on one side is received on
VLAN 2 on the other. VLAN 1 ???leaks??? into the VLAN 2 segment. There is no reason this
behavior would be required, and connectivity issues will occur in the network if a native
VLAN mismatch exists.
Trunk Mode Mismatches
You should statically con?¬?gure trunk links whenever possible.
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