V-273690

Discussion

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.

Check Content

Review the switch configuration and verify that the default VLAN is pruned from trunk links that do not require it.

device#show vlan 888
PORT-VLAN 888, Name DEFAULT-VLAN, Priority level0, On
 Untagged Ports: (U1/M1)   1   2   3   4   5   6   7   8   9  10  11  12 
 Untagged Ports: (U1/M1)  13  14  15  16  17  18  19  20  21  22  23  24 
 Untagged Ports: (U1/M1)  25  26  27  28  29  30  31  32  33  34  35  36 
 Untagged Ports: (U1/M1)  37  38  39  40  41  43  44  45  46  47  48 
 Untagged Ports: (U1/M2)   1   2   3   4   5   6   7   8
   Tagged Ports: None
 Mac-Vlan Ports: None
     Monitoring: Disabled
device#

If the default VLAN is not pruned from trunk links that should not be transporting frames for the VLAN, this is a finding.