ZyXEL P-2812HNU-F1 User Guide - Page 291

Network Size, Notation

Page 291 highlights

Appendix A IP Addresses and Subnetting 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 95 Subnet Masks BINARY 8-bit mask 16-bit mask 24-bit mask 29-bit mask 1ST OCTET 11111111 11111111 11111111 11111111 2ND OCTET 3RD OCTET 00000000 00000000 11111111 00000000 11111111 11111111 11111111 11111111 4TH OCTET 00000000 00000000 00000000 11111000 DECIMAL 255.0.0.0 255.255.0.0 255.255.255.0 255.255.255.248 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). As these two IP addresses cannot be used for individual hosts, calculate the maximum number of possible hosts in a network as follows: Table 96 Maximum Host Numbers SUBNET MASK HOST ID SIZE 8 bits 16 bits 24 bits 29 bits 255.0.0.0 255.255.0.0 255.255.255.0 255.255.255.248 24 bits 16 bits 8 bits 3 bits 224 - 2 216 - 2 28 - 2 23 - 2 MAXIMUM NUMBER OF HOSTS 16777214 65534 254 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. P-2812HNU(L)-Fx Series User's Guide 291

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Appendix A IP Addresses and Subnetting
P-2812HNU(L)-Fx Series User’s Guide
291
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.
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).
As these two IP addresses cannot be used for individual hosts, calculate the maximum number of
possible hosts in a network as follows:
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.
Table 95
Subnet Masks
BINARY
DECIMAL
1ST OCTET
2ND OCTET
3RD OCTET
4TH OCTET
8-bit mask
11111111
00000000
00000000
00000000
255.0.0.0
16-bit mask
11111111
11111111
00000000
00000000
255.255.0.0
24-bit mask
11111111
11111111
11111111
00000000
255.255.255.0
29-bit mask
11111111
11111111
11111111
11111000
255.255.255.248
Table 96
Maximum Host Numbers
SUBNET MASK
HOST ID SIZE
MAXIMUM NUMBER OF
HOSTS
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