This material was developed with funding from the
National Science Foundation under Grant # DUE 1601612
Default Subnet Mask
Range of a Class A Network Addresses 1.x.x.x – 126.x.x.x
A default Class A subnet mask uses the first octet to identify the network portion of a Class A IP address and the last three octets are the host portion of the address.
16,777,216 Hosts Per Network
The number of bits borrowed determines the new subnet mask. For example, borrowing 12 bits from a Class A network results in the following:
Default Class A subnet mask = 255.0.0.0 The new subnet mask with 12 borrowed bits = 255.255.240.0
255.255.240.0 represented as a bitwise mask = /20
Note: The bitwise mask value equals the default subnet mask bits (8) plus the borrowed bits (12).
You can write 220.127.116.11 255.255.240.0 as 18.104.22.168 /20
Drag the slider to view the number of bits borrowed.