Dell PowerEdge C6145 Hardware Owner's Manual page 89

Subnet Mask Configuration
Select Subnet Mask item in the IPMI Configuration screen to view the
following submenu:
Option
Subnet Mask
NOTE: When BMC IP status is static, this item is userful.
Description
Enter Subnet Mask in decimal in the form of
XXX.XXX.XXX.XXX (XXX less than 256 and in
decimal only).
Using the System Setup Program | 89