Huawei Quidway S5000 Series Operation Manual - Getting Started page 32

Operation Manual - Getting Started
Quidway S5000 Series Ethernet Switches
II. Subnet and mask
As the Internet develops so fast, the IP address resource is exhausting. The traditional
IP address assignment wastes too much. The concepts of address mask and subnet
are raised to make good use of the IP address.
The mask is a 32-bit number corresponding to the IP address, containing some 1s and
0s. Basically, you can arrange the 1s and 0s in any order, however, the first several bits
are set to 1s normally. The mask can separate the IP address into two parts, subnet
address and host address. The part of IP address corresponds to the 1 of mask is
subnet address, and the remain part is the host address. If there is no sub-net division,
then its sub-net mask is the default value and the length of "1" indicates the net-id
length. Therefore, for IP addresses of classes A, B and C, the default values of
corresponding sub-net mask are 255.0.0.0, 255.255.0.0 and 255.255.255.0
respectively.
With mask, a Class A network containing more than 16 million hosts and a Class B
network containing more than 60 thousand hosts can be divided into many small
networks, each of them is called a subnet. For example, with help of the mask
255.255.224.0, a Class A network at 202.38.0.0 can be divided into to 8 subnets,
202.38.0.0, 202.38.32.0, 202.38.64.0, 202.38.96.0, 202.38.128.0, 202.38.160.0,
202.38.192.0, and 202.38.224.0. (See the figure below.) Every subnet can contain
more than 8000 hosts.
C la ss B
2 02.3 8.0.0
S tan d ard
m as k
255 .2 55.0.0
S u bn e t m a sk
2 55.2 55.22 4.0
S u bne t addre ss:
000
001
010
011
100
101
110
111
Figure 5-2 Divide subnet for IP address
11001010, 00100110, 000 00000, 00000000
11111111, 11111111, 000 00000, 00000000
11111111, 11111111, 111 00000, 00000000
S ubnet address: 202.38. 0.
S ubnet address: 202.38. 3 2.
S ubnet address: 202.38. 6 4.
S ubnet address: 202.38. 9 6.
S ubnet address: 202.38.12 8.
S ubnet address: 202.38.16 0.
S ubnet address: 202.38.19 2.
S ubnet address: 202.38.22 4.
Chapter 5 System IP Configuration
Subnet H ost
num b er
n um be r
0
0
0
0
0
0
0
0
5-3