3Com Switch 8800 Family Configuration Guide

Configuring IP Address 73
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, the
first consecutive bits are set to 1s when you design a mask. The mask divides the IP
address into two parts: subnet address and host address. The part of IP address
that corresponds to the bits 1s in the mask indicates the subnet address and the
other part of IP address indicate the host 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 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
(Refer to the following figure). Each subnet can contain more than 8000 hosts.
Figure 15 Subnet division of an IP address
Configuring IP
Address
The following sections describe IP address configuration tasks:
■ “Configuring the Hostname and Host IP Address”
■ “Configuring the IP Address of the VLAN Interface”
■ “IP Address Protection Configuration”
■ “Configuring Whether the Switch Sends Unreachable Packets”
Configuring the
Hostname and Host IP
Address
Using this command, you can associate a host name with an IP address. After that,
when using an application like telnet, you can use the host name instead of the IP
address that is hard to memorize, and the system automatically translates the host
name to the IP address.
Perform the following configuration in system view.
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: