Step 4: Isolate VLAN and Trunking Problems

A switch’s forwarding process depends on both the definitions of access VLANs on access interfaces and on VLAN trunks that can pass traffic for many VLANs. In addition, before a switch can forward frames in a particular VLAN, the switch must know about a VLAN, either through configuration or VTP, and the VLAN must be active. The following sections examine some of the tools regarding all these VLAN-related issues. This configuration step includes the following steps:

Step 4. Check VLANs and VLAN trunks as follows:

A. Identify all access interfaces and their assigned access VLANs, and reassign into the correct VLANs as needed.

B. Determine whether the VLANs both exist (configured or learned with VTP) and ...

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