The attribute isImpactPropOverVLANEnabled of a VLAN decides whether a VLAN should take part in an impact propagation or not. Because this attribute is set to True by default for all VLANs, all VLANs takes part in the impact propagation. Devices sharing the same VLAN may have an impact on each other. However, you may want to prevent the impact propagation through some VLANs, such as management VLANs and default VLANs.