Cisco CCNA mock exam questions sample test – Question 227

.How many IP addresses are available for hosts in the 192.168.16.64 /26 subnet?

A. 14
B. 30
C. 62
D. 126

Correct Answer: C

Explanation:
There are 62 IP addresses available for hosts in the 192.168.16.64 /26 subnet.
The number of host addresses is calculated as 2n – 2, where n is the number of host bits and 2 is subtracted to exclude the network address and the broadcast address.
An IP address has 32 available bits divided into four octets. In the 192.168.16.66 /26 address, the /26 indicates that there are 26 masking bits, or that 26 bits are reserved for the
network portion of the address. This leaves 6 bits for the host addresses (32 – 26 = 6).
The following formula is used to calculate the number of IP addresses available for hosts:
Network address: 192.168.16.0
Subnet mask in decimal: 255.255.255.192
Subnet mask in binary: 11111111.11111111.1111111.11000000
Number of bits used for masking = 26
Number of hosts bits in the address = 6
Using the formula for calculating the number of hosts per subnet, we find:
Hosts formula: 2number-of-host-bits – 2
Hosts: 26 – 2 = 62
For subnet 192.168.16.64, the valid host range starts from 192.168.16.65 and runs to 192.168.16.126. For subnet 192.168.16.128, the valid host range starts from 192.168.16.129
and runs to 192.168.16.190.
The options 14, 30, and 126 are incorrect because 62 IP addresses are available for hosts in the 192.168.16.64/26 subnet.
The correct mask for the size network desired is critical to proper network function. For example, assume a router has an interface Fa0/0 hosting a LAN with 20 computers configured
as shown in the following output of show interfaces command:
Router# show interfaces
Fastethernet0 is up, line protocol is up
Hardware address is 000b.12bb.4587
Internet address 192.168.10.30/30
In this example, the computers will not be able to access anything beyond the LAN because the mask /30 only allows for 2 addresses when 21 (including the router interface) are
required.
Objective:
Network Fundamentals
Sub-Objective:
Apply troubleshooting methodologies to resolve problems
References:
Cisco > Technology Support > IP > IP Routing > Design TechNotes > IP Addressing and Subnetting for New Users > Document ID: 13788 > Understanding IP Addresses