ZyXEL N4100 Guia Do Utilizador
Appendix C IP Addresses and Subnetting
N4100 User’s Guide
303
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.
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.
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.
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.
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).
(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:
maximum number of possible hosts in a network as follows:
Table 76 Subnet Masks
BINARY
DECIMAL
1ST
OCTET
OCTET
2ND
OCTET
OCTET
3RD
OCTET
OCTET
4TH
OCTET
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 77 Maximum Host Numbers
SUBNET MASK
HOST ID SIZE
MAXIMUM NUMBER OF
HOSTS
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