This read-create OCTET STRING (4 bytes) sets the mask to apply to the customer VLAN identifier prvtSuperVlanIfCVlanId for this Super-VLAN entry, with an all-zeros value meaning no mask is applied. Admins use it to match a range of customer VLAN IDs with a single table entry instead of enumerating every VLAN individually, similar to how a subnet mask groups addresses. For example, an admin wanting a single entry to cover VLANs 100-107 could set an appropriate mask value instead of creating eight separate prvtSuperVlanIfCVlanEntry rows.