Information
The default VLAN (i.e., VLAN 1) is a special VLAN used for control plane traffic such as Spanning-Tree Protocol (STP), Dynamic Trunking Protocol (DTP), VLAN Trunking Protocol (VTP), and Port Aggregation Protocol (PAgP). VLAN 1 is enabled on all trunks and ports by default. With larger campus networks, care needs to be taken about the diameter of the STP domain for the default VLAN. Instability in one part of the network could affect the default VLAN, thereby influencing control-plane stability and therefore STP stability for all other VLANs.
NOTE: Nessus has not performed this check. Please review the benchmark to ensure target compliance.
Solution
Step 1: Prune VLAN 1 from any trunk links as necessary.
SW1(config)# int e1/2
SW1(config-if)# switchport trunk allowed vlan except 1, 999
SW1(config-if)# end
Step 2: Verify VLAN 1 is not allowed on the trunk link.
SW1# show interface trunk
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Port Native Status Port
Vlan Channel
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Eth1/1 1 trunking --
Eth1/2 1 trunking --
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Port Vlans Allowed on Trunk
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Eth1/1 1-998,1000-4094
Eth1/2 2-998,1000-4094