Huawei Quidway S6500 Series Operation Manual page 94

Operation Manual - Network Protocol
Quidway S6500 Series Ethernet Switches
1.1.2 Subnet and Mask
Nowadays, with rapid development of the Internet, IP addresses are depleting very fast.
The traditional IP address allocation method wastes IP addresses greatly. In order to
make full use of the available IP addresses, the concept of mask and subnet is
proposed.
A mask is a 32-bit number corresponding to an IP address. The number consists of 1s
and 0s. Principally, these 1s and 0s can be combined randomly. However, when you
design masks, the bit values of network numbers and subnet numbers are set to 1s,
and the bit values of host numbers are set to 0s. The mask divides the IP address into
two parts: subnet address and host address. The bits 1s in the address and the mask
indicate the subnet address and the other bits indicate 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.
The mask can be used to divide a Class A network containing more than 16,000,000
hosts or a Class B network containing more than 60,000 hosts into multiple small
networks. Each small network is called a subnet. For example, for the Class B network
address 138.38.0.0, the mask 255.255.224.0 can be used to divide the network into 8
subnets:
138.38.160.0, 138.38.192.0 and 138.38.224.0 (Refer to the following figure). Each
subnet can contain more than 8000 hosts.
ClassB ClassB
138.38.0.0 138.38.0.0
Standard Standard
mask mask
255.255.0.0 255.255.0.0
Subnet mask Subnet mask
255.255.224.0 255.255.224.0
Subnet address: Subnet address: Subnet address: Subnet address:
000 000
001 001
010 010
011 011
100 100
101 101
110 110
111 111
Figure 1-2 Subnet division of IP address
138.38.0.0, 138.38.32.0,
10001010, 00100110, 000 00000, 0000 10001010, 00100110, 000 00000, 0000
11111111, 11111111, 000 00000, 0000 11111111, 11111111, 000 00000, 0000
11111111, 11111111, 111 00000, 00000000 11111111, 11111111, 111 00000, 00000000
Subnet address: 138.38. Subnet address: 138.38. 0. 0.
Subnet address: 138.38. 32. Subnet address: 138.38. 32.
Subnet address: 138.38. 64. Subnet address: 138.38. 64.
Subnet address: 138.38. 96. Subnet address: 138.38. 96.
Subnet address: 138.38.128. Subnet address: 138.38.128.
Subnet address: 138.38.160. Subnet address: 138.38.160.
Subnet address: 138.38.192. Subnet address: 138.38.192.
Subnet address: 138.38.224. Subnet address: 138.38.224.
Huawei Technologies Proprietary
Chapter 1 IP Address Configuration
138.38.64.0, 138.38.96.0,
0000 0000
0000 0000
Subnet Subnet
Host Host
number number
num ber num ber
0 0
0 0
0 0
0 0
0 0
0 0
0 0
0 0
1-3
138.38.128.0,