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IP Address Configuration 271
address. If there is no subnet division, then its subnet 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 subnet 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: 138.38.0.0, 202.38.32.0, 138.38.64.0, 138.38.96.0, 138.38.128.0,
138.38.160.0, 138.38.192.0 and 138.38.224.0 (Refer to the Figure 62). Each subnet
can contain more than 8000 hosts.
Figure 62 Subnet Division of IP Address
Configuring IP Address Configure an IP address for a VLAN interface in one of three ways:
■ Using the IP address configuration command
■ Allocated by BOOTP server
■ Allocated by DHCP server
These three methods are mutually exclusive and a new configuration will replace the
current IP address. For example, if you apply for an IP address using the
ip address
bootp-alloc
command, the address allocated by BOOTP shall replace the
currently-configured IP address.
This section introduces how to configure an IP address with the IP address
configuration command. The other two methods are described in subsequent
chapters.
The IP address configuration is described in the following sections:
■ Configuring the Hostname and Host IP Address
■ Configuring the IP Address of the VLAN Interface
Configuring the Hostname and Host IP Address
The host name is corresponded to the IP address by using this command. When you
use applications like Telnet, you can use the host name without having to memorize
the IP address since the system translates it to the IP address automatically.
10001010, 00100110, 000 00000, 00000000
ClassB
138.38.0.0
Subnet mask
255.255.224.0
11111111, 11111111, 111 00000, 00000000
11111111, 11111111, 000 00000, 00000000
Standard
mask
255.255.0.0
Subnet address:
000 Subnet address: 138.38. 0. 0
001 Subnet address: 138.38. 32. 0
010 Subnet address: 138.38. 64. 0
011 Subnet address: 138.38. 96. 0
100 Subnet address: 138.38.128. 0
101 Subnet address: 138.38.160. 0
110 Subnet address: 138.38.192. 0
111 Subnet address: 138.38.224. 0
Subnet
number
Host
number
Subnet address:
10001010, 00100110, 000 00000, 00000000
ClassB
138.38.0.0
Subnet mask
255.255.224.0
11111111, 11111111, 111 00000, 00000000
11111111, 11111111, 000 00000, 00000000
Standard
mask
255.255.0.0
Subnet address:
000 Subnet address: 138.38. 0. 0
001 Subnet address: 138.38. 32. 0
010 Subnet address: 138.38. 64. 0
011 Subnet address: 138.38. 96. 0
100 Subnet address: 138.38.128. 0
101 Subnet address: 138.38.160. 0
110 Subnet address: 138.38.192. 0
111 Subnet address: 138.38.224. 0
Subnet
number
Host
number
Subnet address: