Understanding VLAN 1
It is important to understand the significance of VLAN 1. By default, all switch ports are part of VLAN 1. VLAN 1 contains control plane traffic and can contain user traffic. It is recommended that user traffic be configured on VLANs other than VLAN 1, primarily to prevent unnecessary user broadcast and multicast traffic from being processed by the Network Management Processor (NMP) of the supervisor. Although VLAN 1 user traffic can be pruned from a trunk, it is not the case with control plane traffic. In fact, in older Cisco Catalyst Software versions (5.4 or earlier), VLAN 1 could not be removed at all from a trunk. Control plane traffic such as VTP, CDP, and PAgP protocols are tagged with VLAN 1 information and are forwarded ...
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