This value controls whether IP Source Guard applies to all VLANs on an interface by default: notAllVlan(0) means only the VLAN explicitly designated by zxr10IPSourceGuardVLAN is covered, allVlan(1) means every VLAN on that interface is covered, and it must be set together with zxr10IPSourceGuardMode per the source description. A network administrator sets this to allVlan(1) when they want blanket source-guard protection across an entire trunk port rather than configuring individual VLANs one at a time. For example, setting zxr10IPSourceGuardDefaultVLAN to allVlan(1) on a trunk port extends source-guard checking to every VLAN carried on that port at once.