Specify the TCP/IP interface network mask of the HMC adapter.
The TCP/IP network mask, combined with the TCP/IP address, identifies the subnetwork in which the HMC adapter is located.
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.