Final answer:
The wildcard mask in OSPF configuration is an inverted form of the network's subnet mask. It is used alongside the network command in OSPF to specify which interfaces on a network participate in routing updates. For instance, a subnet mask of 255.255.255.0 would have a corresponding wildcard mask of 0.0.0.255.
Step-by-step explanation:
The wildcard mask used to advertise a network in an OSPF (Open Shortest Path First) configuration depends on the network's subnet mask. A wildcard mask is an inverted subnet mask; it has ones where the subnet mask has zeros and vice versa. For example, if the subnet mask is 255.255.255.0, the corresponding wildcard mask would be 0.0.0.255. This is because the binary representation of the subnet mask consists of 24 ones followed by 8 zeros. When inverted for a wildcard mask, this sequence becomes 24 zeros followed by 8 ones.
In OSPF configurations, the wildcard mask is used with the network command to specify which interfaces participate in OSPF for a given network. If you wish to include all interfaces in a subnet, you would use precisely calculated wildcard mask. However, if selective interfaces on the same subnet are intended for OSPF, then more specific wildcard masks are required.