User's Manual

SPEEDLAN 9000 Installation and Operation User Guide
5-6 Basics of IP Addressing
Diagram of Subnetting a Network
Still confused?
An easier method to explain this concept is to use the classic "mailing" analogy used in IP
addressing. Consider that this network, called Long Street, is four blocks long. There are 254 houses
on Long Street, and each block contains 64 houses. Houses 1 to 63 reside on Block A. Houses 64
to 127 reside on Block B. Houses 128 to 191 reside on Block C. Houses 192 to 254 reside on
Block D. Think of each block as a subnet. This means that Blocks A, B, C, and D are all part of Long
Street, which is also known as the network in this example. The mailman would organize the letters
(or IP addresses for network equipment) by creating four piles (one for each block, or subnet). As
soon as the mailman picks up pile A in his hand, he knows which block to turn on. This same
reasoning applies to piles B, C, and D as well. Unit/Router D knows exactly which subnet to transfer
(or turn) the packets to by reading its IP and subnet mask address. Note that each subnet on this
network is 255.255.255.192. Why is 192 the last octet in the subnet mask and not 64? The last
octet, 192, is the mask that allows 64 "houses" to know that the mailman (or unit/router) is coming
in advance. The "houses" will know it's mailman "Jim" by looking at the IP number.
Internet
Router D
Router B
Router C
Computer Computer
Computer
Computer
Computer Computer Computer
Computer Computer Computer
Long Street
Subnet A
IP Address: 195.172.3.1
Subnet Mask: 255.255.255.192
Subnet B
IP Address: 195.172.3.64
Subnet Mask: 255.255.255.192
Subnet C
IP Address: 195.172.3.128
Subnet Mask: 255.255.255.192
Subnet D
IP Address: 195.172.3.192
Subnet Mask: 255.255.255.192
Router A