260 Chapter 5: Network Protocols
Figure 5-23
Sample Network Using Class A, B, and C Network Numbers
Decimal Algorithm for Deriving the Valid Subnets with Basic Subnetting
Time counts when taking the CCNA exam, so it's a good idea to take advantage of the easier
decimal algorithms to derive facts about subnetting. The algorithm for deriving the subnet
numbers of a network, given a static, basic mask, is extremely intuitive. Two cases for the
decimal algorithm will be examined here: a Class A network subnetted using mask 255.255.0.0,
and a Class B network subnetted using mask 255.255.255.0:
Step 1
Write down the 1 or 2 bytes of the network number.
Step 2
Leave a space immediately to the right to add a value in the next
octet.
150.150.1.0
150.150.2.0
150.150.6.0
150.150.4.0
150.150.3.0
Sioux Falls
Atlanta
Vinnie
Snellville
A
C
D
Barnesville
Frame
Relay
150.150.5.0
B
Ray
Fay
Kris
Wendell
Matt
ch05.fm Page 260 Monday, March 20, 2000 5:06 PM