This is a wildcard mask, Cisco ACL-style, where 0 bits mean must match and 1 bits mean do not care, applied against cfgFilterNetworkAddress, with a mask of zero meaning only an exact match of that address qualifies, matching no range at all. Because this uses inverted wildcard-mask logic rather than a standard subnet mask, an admin used to conventional netmasks could easily configure the opposite of what they intended if they do not account for the inversion, silently broadening or narrowing the actual match scope. To match an entire /24 subnet like 192.168.10.0, this mask would need to be set to 0.0.0.255 in Cisco wildcard style, not 255.255.255.0 as a standard subnet mask user might instinctively enter.