ICND1 Subnetting 5 — Questions and Answers
Question 1: Which address is the network address of the subnet containing host 192.168.100.77/28?
- 192.168.100.64 (Correct answer)
- 192.168.100.72
- 192.168.100.80
- 192.168.100.48
Correct answer: 192.168.100.64
A /28 has a block size of 16; 77 ÷ 16 = 4 remainder 13, so the subnet starts at 4 × 16 = 64.
Question 2: What CIDR notation represents the subnet mask 255.255.255.192?
- /26 (Correct answer)
- /25
- /27
- /28
Correct answer: /26
255.255.255.192 has 26 bits set (24 + 2 from the last octet: 11000000), giving /26.
Question 3: You have 10.0.0.0/8 and need to create subnets for WAN links using the least address space. Which mask is most efficient for a two-router serial link?
- /30 (Correct answer)
- /24
- /28
- /16
Correct answer: /30
A /30 provides exactly 2 usable host addresses, which is precisely what a point-to-point WAN link requires.
Question 4: If a router has the interface IP 172.20.0.1/23, which network does it belong to?
- 172.20.0.0 (Correct answer)
- 172.20.1.0
- 172.20.2.0
- 172.20.0.1
Correct answer: 172.20.0.0
A /23 has a block size of 2 in the third octet; 0 ÷ 2 = 0, so the network is 172.20.0.0.
Question 5: How many subnets and hosts per subnet does 10.0.0.0/8 subnetted to /12 provide?
- 16 subnets, 1,048,574 hosts each (Correct answer)
- 4 subnets, 2,097,150 hosts each
- 32 subnets, 524,286 hosts each
- 8 subnets, 1,048,574 hosts each
Correct answer: 16 subnets, 1,048,574 hosts each
12 - 8 = 4 borrowed bits → 2^4 = 16 subnets; 32 - 12 = 20 host bits → 2^20 - 2 = 1,048,574 hosts each.
Question 6: A technician enters 'ip address 192.168.1.33 255.255.255.224' on an interface. What is the valid host range for this subnet?
- 192.168.1.33 – 192.168.1.62 (Correct answer)
- 192.168.1.1 – 192.168.1.30
- 192.168.1.33 – 192.168.1.63
- 192.168.1.32 – 192.168.1.63
Correct answer: 192.168.1.33 – 192.168.1.62
255.255.255.224 is /27 with a block of 32; the subnet containing .33 starts at .32, so hosts are .33–.62 (.63 is broadcast).
Question 7: Which of the following is TRUE about the subnet 0.0.0.0/0?
- It represents the default route matching all IP addresses (Correct answer)
- It is an invalid subnet in TCP/IP
- It represents only the loopback network
- It matches only private IP addresses
Correct answer: It represents the default route matching all IP addresses
0.0.0.0/0 has no bits fixed, so it matches every possible IP address and is used as the default route.
ICND1 Subnetting 5
Which address is the network address of the subnet containing host 192.168.100.77/28?