ZyXEL P-660HN-51 User Guide - Page 272

Subnet Masks

Page 272 highlights

Appendix B IP Addresses and Subnetting 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. Figure 147 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). Table 99 Subnet Masks 1ST OCTET: 2ND OCTET: 3RD OCTET: 4TH OCTET IP Address (Binary) Subnet Mask (Binary) Network Number Host ID (192) (168) (1) (2) 11000000 10101000 00000001 00000010 11111111 11111111 11111111 00000000 11000000 10101000 00000001 00000010 272 P-660HN-TxA User's Guide

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Appendix B IP Addresses and Subnetting
P-660HN-TxA User’s Guide
272
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.
Figure 147
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).
Table 99
Subnet Masks
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
Network Number
11000000
10101000
00000001
Host ID
00000010