B IP A DDRESSINGIntroduction to IPAddressingThis section contains a brief introduction to the IP addressing scheme foradministrators that are new to the IP protocol.IP Addressing Basics IP addresses are 32 bits long and generally written in what is calleddotted decimal notation: four decimal values separated by periods. Forexample: 192.77.203.5.Address Classes In IP, the same 32 bits can be divided in a number of different ways toindicate networks and sub-networks of different sizes. The IP Network isidentified by the number of bits in the network mask. The node addressesare not physical addresses of your network interface cards, but arbitrarynumbers that are mapped to those physical addresses later. This allowsyou to accommodate varying network structures from a small number ofnetwork segments with huge numbers of nodes to large numbers ofnetworks with only a few nodes.Subnetting A large IP network can be subdivided into smaller subnetworks. This isdone using a subnet mask (in this text, often called netmask), which tellsa routing device how to further subdivide the Host ID portion of an IPaddress.A subnet mask is a 32-bit value which also can be written in dotteddecimal notation. It contains a number of bits set to 1 (indicating thenetwork portion of an address) followed by a number of bits set to 0(indicating the host portion of an address).For example, a netmask of 255.255.255.0 on a Class B network wouldindicate that the network is divided into 254 sub-networks of 254 nodeseach (0 and 255 are reserved numbers). For example, 128.5.63.28 would840ug.book Page 1 Friday, July 7, 2000 2:23 PM
