Specify the Network Mask to use to allow access. The Network Mask combines with the TCP/IP address to identify the subnetwork for the HMC location.
The network mask is a 32-bit dotted-decimal
number indicating the range of IP addresses residing on a single
IP network/subnet/supernet.
It must be specified in the format
nnn.nnn.nnn.nnn:
where nnn is specified as zero (0), 128, 192, 224, 240, 248, 252, 254 or, 255.
Additionally, if nnn is specified as a value other than 255, each number to the right of it, if any, must be zero (0). For example: 255.255.255.0
If you do not know or are not sure of the HMC IP address/network mask, contact your system administrator.