3Com OfficeConnect 3C892 User Manual

Also see for 3C892 - OfficeConnect ISDN Lan Modem Router: User guide Getting started guide Setting up

Contents

3Com OfficeConnect 3C892 User Manual Manual pdf 108 page image

108 A PPENDIX A: N ETWORKING PRIMERWhat is an IP Address? An IP address is a 32 bit address used by TCP/IP to uniquely identify the location ofa device on a network. Note that the IP address does not refer to the device itself.If, for example, you relocate a PC to another area of the same network, you mayneed a new IP address.The structure of this 32-bit address varies depending upon the size of the networkon which the device is located. From largest to smallest, network types arereferred to as Class A, Class B, Class C, and Class D. Within each class, a certainnumber of bits identifies the class, the network and the local address. Forexample, in a Class C network, the first three bits (110) identify the network typeas Class C. The next 21 bits identify the network and the last eight represent thelocal or host address limiting the number of devices to 256. In contrast, a Class Anetwork 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.The IP address of the ISDN LAN Modem identifies the ISDN LAN Modem itself andthe network it creates when devices are connected to the Ethernet ports.What is a Subnet Mask? Many networks are divided further into smaller sub networks. A subnet mask is anumber that identifies the sub network to which your computer is connected. Thesubnet mask differentiates the part of the IP address that represents the networkand the part that represents the host.The bits of the subnet mask are set to 1 if the host should treat the correspondingbit in the IP address as part of the original network number. These bits in the maskare set to 0 if the host should treat the bits as part of the device number as shownin Figure 58.Figure 58 Subnet MaskDynamic and Static IPAddressesIP addresses for public networks must be unique and provided by the NetworkInformation Center (NIC). Because of the increasing popularity of the Internet, theNIC is running out of permanent IP addresses. It is therefore becoming morecommon to use dynamic IP addresses which are assigned temporarily and thenreused, instead of static IP addresses which are permanent. For example, whenyou access the Internet, your ISP has a pool of IP addresses it uses to providetemporary 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 ownunique (that is, private) IP address numbering. IP addresses for private networkssuch as an office LAN must also be unique but only within that LAN.IP Address Network Number Device NumberSubnet Mask 11111111 11111111 11111111 00000000Subnet Address Network Number Subnet DeviceNumber