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Appendix B IP Addresses and Subnetting
FSG1100HN User’s Guide
115
The following figure shows an example IP address in which the first three octets
(192.168.1) are the network number, and the fourth octet (16) is the host ID.
Network Number and Host ID
How much of the IP address is the network number and how much is the host ID
varies according to the subnet mask.
Subnet Masks
A subnet mask is used to determine which bits are part of the network number,
and which bits are part of the host ID (using a logical AND operation). The term
“subnet” is short for “sub-network”.
A subnet mask has 32 bits. If a bit in the subnet mask is a “1” then the
corresponding bit in the IP address is part of the network number. If a bit in the
subnet mask is “0” then the corresponding bit in the IP address is part of the
host ID.
The following example shows a subnet mask identifying the network number (in
bold text) and host ID of an IP address (192.168.1.2 in decimal).
Subnet Mask - Identifying Network Number
1ST
OCTET:
(192)
2ND
OCTET:
(168)
3RD
OCTET:
(1)
4TH
OCTET:
(2)
IP Address (Binary)
11000000
10101000
00000001
00000010
Subnet Mask (Binary)
11111111
11111111
11111111
00000000