Appendix E IP Addresses and Subnetting

Table 100 Subnet Masks

 

1ST

2ND

3RD

4TH

 

OCTET:

OCTET:

OCTET:

OCTET

 

(192)

(168)

(1)

(2)

Network Number

11000000

10101000

00000001

 

 

 

 

 

 

Host ID

 

 

 

00000010

 

 

 

 

 

By convention, subnet masks always consist of a continuous sequence of ones beginning from the leftmost bit of the mask, followed by a continuous sequence of zeros, for a total number of 32 bits.

Subnet masks can be referred to by the size of the network number part (the bits with a “1” value). For example, an “8-bit mask” means that the first 8 bits of the mask are ones and the remaining 24 bits are zeroes.

Subnet masks are expressed in dotted decimal notation just like IP addresses. The following examples show the binary and decimal notation for 8-bit, 16-bit, 24-bit and 29-bit subnet masks.

Table 101

Subnet Masks

 

 

 

 

BINARY

 

 

 

 

 

1ST

2ND

3RD

4TH

DECIMAL

 

OCTET

OCTET

OCTET

OCTET

 

8-bit mask

11111111

00000000

00000000

00000000

255.0.0.0

 

 

 

 

 

 

16-bit

11111111

11111111

00000000

00000000

255.255.0.0

mask

 

 

 

 

 

 

 

 

 

 

 

24-bit

11111111

11111111

11111111

00000000

255.255.255.0

mask

 

 

 

 

 

 

 

 

 

 

 

29-bit

11111111

11111111

11111111

11111000

255.255.255.24

mask

 

 

 

 

8

 

 

 

 

 

 

Network Size

The size of the network number determines the maximum number of possible hosts you can have on your network. The larger the number of network number bits, the smaller the number of remaining host ID bits.

An IP address with host IDs of all zeros is the IP address of the network (192.168.1.0 with a 24-bit subnet mask, for example). An IP address with host IDs of all ones is the broadcast address for that network (192.168.1.255 with a 24-bit subnet mask, for example).

 

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NWA-3500/NWA-3550 User’s Guide