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Native VLAN Mismatch!

Binary FreakBinary Freak Member Posts: 37 ■■□□□□□□□□
in CCNA & CCENT
What are the main reasons for a Native VLAN mismatch on FA interfaces, and how can they be fixed?crash.gif

Thanks,

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    OfWolfAndManOfWolfAndMan Member Posts: 923 ■■■■□□□□□□
    Native VLAN by default is 1, so to create a mismatch, the native vlan must be configured manually on one side (ISL does not support the native VLAN. Only dot1q). One of the most common reasons not to have this mismatch is because of the following below:

    VLAN hopping - Wikipedia, the free encyclopedia

    Look specifically at double tagging.
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    AwesomeGarrettAwesomeGarrett Member Posts: 257
    It mostly happens when trying to save CPU cycles by having the data VLAN go untagged. Therefore the switch does have to encapsulate or strip the tag as traffic traverses the switch.

    Not really needed these days with better performing access layer switches. Caution! Easy way to start a loop even in a lab.
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    theodoxatheodoxa Member Posts: 1,340 ■■■■□□□□□□
    (config-if)# switchport trunk native vlan <vlan>

    Somebody probably entered this command on one or both sides with different VLANs specified.
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