Appendix B IP Addresses and Subnetting

As these two IP addresses cannot be used for individual hosts, calculate the maximum number of possible hosts in a network as follows:

Table 56 Maximum Host Numbers

SUBNET MASK

HOST ID SIZE

 

MAXIMUM NUMBER OF

 

HOSTS

 

 

 

 

8 bits

255.0.0.0

24 bits

224 – 2

16777214

16 bits

255.255.0.0

16 bits

216 – 2

65534

24 bits

255.255.255.0

8 bits

28 – 2

254

29 bits

255.255.255.248

3 bits

23 – 2

6

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 57 Alternative Subnet Mask Notation

SUBNET MASK

ALTERNATIVE

LAST OCTET

LAST OCTET

NOTATION

(BINARY)

(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

 

 

 

 

Subnetting

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.

168

 

GS1510 Series User’s Guide