CCNA Cisco Certified Network Associate Study Guide - FTP Server

154 Chapter 3 � Internet Protocol
the preceding “IP Addressing” section, which shows you how to determine the
difference between the subnet and host bits.
Practice Example 1: 255.255.0.0
Class A addresses use a default mask of 255.0.0.0, which leaves 22 bits for
subnetting since you must leave two bits for host addressing. The
255.255.0.0 mask with a Class A address is using eight subnet bits.
1. 2 8 –2=254.
2. 2 16 –2=65, 534.
3. 256–255=1, 2, 3, etc. (all in the second octet). The subnets would be
10.1.0.0, 10.2.0.0, 10.3.0.0, etc., up to 10.254.0.0.
4. First find the broadcast addresses in step 5, then come back and perform
step 4 by filling in the host addresses.
5. Find the broadcast address of each subnet, which is always the number
right before the next subnet.
Table 3.8 shows the first and last subnet, valid host range, and broadcast
addresses.
TABLE 3.8 The First and Last Subnet
Practice Example 2: 255.255.240.0
255.255.240.0 gives us 12 bits of subnetting and leaves us 12 bits for host
addressing.
1. 2 12 –2=4094.
2. 2 12 –2=4094.
First Subnet Last Subnet
Subnet 10.1.0.0 10.254.0.0
First Host 10.1.0.1 10.254.0.1
Last Host 10.1.255.254 10.254.255.254
Broadcast 10.1.255.255 10.254.255.255