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Appendix C IP Addresses and Subnetting
User
’
s Guide
226
As these two IP addresses cannot be used for individual hosts, calculate the
maximum number of possible hosts in a network as follows:
Notation
Since the mask is always a continuous number of ones beginning from the left,
followed by a continuous number of zeros for the remainder of the 32 bit mask,
you can simply specify the number of ones instead of writing the value of each
octet. This is usually specified by writing a
“ / ” followed by the number of bits in
the mask after the address.
For example, 192.1.1.0 /25 is equivalent to saying 192.1.1.0 with subnet mask
255.255.255.128.
The following table shows some possible subnet masks using both notations.
Table 72 Maximum Host Numbers
SUBNET MASK HOST ID SIZE
MAXIMUM NUMBER OF
HOSTS
8 bits 255.0.0.0 24 bits 2
24
– 2 16777214
16 bits 255.255.0.0 16 bits 2
16
– 2 65534
24 bits 255.255.255.0 8 bits 2
8
– 2 254
29 bits 255.255.255.2
48
3 bits 2
3
– 2 6
Table 73 Alternative Subnet Mask Notation
SUBNET
MASK ALTERNATIVE
NOTATION LAST OCTET
(BINARY) LAST OCTET
(DECIMAL)
255.255.255.0 /24 0000 0000 0
255.255.255.12
8 /25 1000 0000 128
255.255.255.19
2 /26 1100 0000 192
255.255.255.22
4 /27 1110 0000 224
255.255.255.24
0 /28 1111 0000 240
255.255.255.24
8 /29 1111 1000 248
255.255.255.25
2 /30 1111 1100 252
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