The broadcast address for Subnet #6 is simply the all 1s host address

or: 

11000001.00000001.00000001.110 11111 = 193.1.1.223 

Again, the broadcast address for Subnet #6 is exactly one less than the

base address for Subnet #7 (193.1.1.224). 

Subnet Example #2

Given

An organization is assigned the network number 140.25.0.0/16 and it

must create a set of subnets that supports up to 60 hosts on each subnet. 

Defining the Subnet Mask / Extended Prefix Length

The first step is to determine the number of bits required to define 60

hosts on each subnet. Since a block of host addresses can only be

assigned along binary boundaries, host address blocks can only be cre 

ated in powers of two. This means that it is impossible to create a block

that contains exactly 60 host addresses. 

To support 60 hosts, the network administrator must define a minimum

address block of 62 (26 2) host addresses. However, this choice would

only provide two unused host addresses on each subnet for future

growth, which is not likely to support additional growth. The network

administrator must define a block of 126 (27 2) host addresses with 66

addresses on each subnet for future growth. A block of 126 host

addresses requires 7 bits in the host number field. 

The next step is to determine the subnet mask/extended prefix length.

Since 7 bits of the 32 bit IP address are required for the host number

field, the extended prefix must be a /25 (25 = 32 7). A 25 bit extended

network prefix can be expressed in dotted decimal notation as

255.255.255.128. This notation is illustrated in Figure 15. 

F I G U R E   1 5 .   E x a m p l e   # 2   D e f i n i n g   t h e   S u b n e t

M a s k / E x t e n d e d   P re f i x   L e n g t h

U N D E R S TA N D I N G   I P   A D D R E S S I N G

1 6