3com 3C886 Manual De Usuario

as Class C. The next 21 bits identify the network and the last 8 represent the local 
or host address, limiting the number of devices to 256. In contrast, a Class A 
network allocates 24 bits for local addresses, allowing for many more devices. 

IP addresses are composed of four sets of eight bits usually separated by a period 
(for example, 192.168.1.1).

The IP address of the 56K LAN Modem identifies the 56K LAN Modem itself and 
the network it creates when devices are connected to the Ethernet ports. 

Many networks are divided further into smaller sub networks. A subnet mask is a 
number that identifies the sub network to which your computer is connected. The 
subnet mask differentiates the part of the IP address that represents the network 
and the part that represents the host. 

The bits of the subnet mask are set to 1 if the host should treat the corresponding 
bit in the IP address as part of the original network number. These bits in the mask 
are set to 0 if the host should treat the bits as part of the device number as shown 
in Figure 46.

Figure 46   Subnet Mask

IP addresses for public networks must be unique and provided by the Network 
Information Center (NIC). Because of the increasing popularity of the Internet, the 
NIC is running out of permanent IP addresses. It is therefore becoming more 
common to use dynamic IP addresses, which are assigned temporarily and then 
reused, instead of static IP addresses which are permanently assigned. For 
example, when accessing the Internet, your ISP has a pool of IP addresses it uses to 
provide temporary connections to multiple users. Once you disconnect from the 
Internet, the IP address you were using is placed back in the pool for use by 
another user.

If your LAN will not connect to the public Internet, you can set up your own 
unique (that is, private) IP address numbering. IP addresses for private networks 
such as an office LAN must also be unique but only within that LAN. 

Dynamic Host Configuration Protocol is a process that automatically assigns a 
unique, temporary IP address to a newly attached computer on an IP network. 

Domain Name Service translates the common alphabetic name into the numeric IP 
address. For example, www.3com.com is translated to an specific IP address by 
DNS. If you do not use the DHCP functionality of the 56K LAN Modem, you will 
have to manually configure the following parameters for each computer on the 
LAN: IP address, subnet mask, DNS address and default gateway.

IP Address               Network Number         Device Number 

Subnet Mask         11111111  11111111    11111111 00000000

Subnet Address      Network Number          Subnet  Device

    Number