User Manual

Appendix B IP Addresses and Subnetting
NBG-418N v2 User’s Guide
162
As these two IP addresses cannot be used for individual hosts, calculate the maximum number of
possible hosts in a network as follows:
Nota tion
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.
Subne tting
You can use subnetting to divide one network into multiple sub-networks. In the following example a
network administrator creates two sub-networks to isolate a group of servers from the rest of the
company network for security reasons.
In this example, the company network address is 192.168.1.0. The first three octets of the address
(192.168.1) are the network number, and the remaining octet is the host ID, allowing a maximum of 2
8
–
2 or 254 possible hosts.
The following figure shows the company network before subnetting.
Table 68 Maximum Host Numbers
SUBNET MASK HO ST ID SIZE MAXIMUM NUMBER O F HO STS
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 255.255.255.248 3 bits 2
3
– 2 6
Table 69 Alternative Subnet Mask Notation
SUBNET MASK
ALTERNATIVE
NO TATION
LAST O CTET
(BINARY)
LAST O CTET
(DECIMAL)
255.255.255.0 /24 0000 0000 0
255.255.255.128 /25 1000 0000 128
255.255.255.192 /26 1100 0000 192
255.255.255.224 /27 1110 0000 224
255.255.255.240 /28 1111 0000 240
255.255.255.248 /29 1111 1000 248
255.255.255.252 /30 1111 1100 252