3Com Switch 7750 Configuration Guide
Configuring an IP Address for a VLAN Interface 129
address, and the part corresponding to the remaining “0” bits in the mask is the
host address. If there is no subnet division, the subnet mask uses the default value
and the length of 1s in the mask is equal to the net-id length. Therefore, for IP
addresses of classes A, B and C, the default values of the corresponding subnet
masks 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 eight subnets: 138.38.0.0, 138.38.32.0, 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 (see
Figure 38). Each subnet can contain more than 8000 hosts.
Figure 38 Subnet division of the IP address
Configuring an IP
Address for a VLAN
Interface
A VLAN interface obtains an IP address with an IP address configuration
command. Generally, it is enough to configure one IP address for a VLAN
interface. However, you can configure up to eight IP addresses for a VLAN
interface so that the interface can be connected to several subnets. Among these
IP addresses, one is the primary IP address and the others are secondary ones.
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:
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:
Table 74 Configure an IP address for a VLAN interface
Operation Command Description
Enter system view system-view -
Enter VLAN interface view interface Vlan-interface vlan-id -
Configure an IP address
for a VLAN interface
ip address ip-address { mask |
mask-length } [ sub ]
Required
By default, a VLAN
interface has no IP address.