How You Discover a Single Network

If you have a single class A, B, or C network address, you can limit Discovery to find only the subnets and IP systems in that network.

Replace the zeros in the subnet filter with an asterisk and provide a value for the subnet mask.
Discovery starts by discovering the local subnet; that is, the subnet to which the local system belongs.
Set the subnet mask to the local subnet mask. You can determine the local subnet mask by looking at the Windows Control Panel, Network, TCP/IP Protocol Setup window. Typically, the subnet mask is 255.255.255.0.
When Discovery finds a router, it uses SNMP to get information on the subnets attached to that router. It adds only those subnets to the MDB that match the subnet filter, and then adds them to the list of subnets to be discovered in the Subnet Management dialog.
To discover only the subnets that you have defined, specify the -S 0 parameter on the dscrvbe command. If you specify -S All or a number greater than 0, the new subnets that are found in a router discovery are also discovered until all known subnets have been discovered, or the number specified is reached.