10 free Cisco 100-150 CCST Networking practice questions with the correct answer and a full explanation for each, taken from the CertStash pack of 75 questions. Work through them, then open each answer to check your reasoning.
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Question 1
Which information is included in the header of a UDP segment?
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Correct answer: A. Port numbers
The UDP segment header contains source and destination port numbers, length, and checksum. Port numbers are essential for identifying the sending and receiving applications. IP addresses exist at the Network layer (Layer 3) and are found in the IP header, not the UDP header. MAC addresses are found at the Data Link layer. Sequence numbers are a TCP feature, not UDP.
Why the other options are wrong
- B. Sequence numbers are part of the TCP header for ordered delivery, not UDP which is connectionless.
- C. IP addresses are contained in the IP header at Layer 3, not the UDP header at Layer 4.
- D. MAC addresses are part of the Data Link layer frame, not the Transport layer UDP segment.
Question 2
Which standard contains the specifications for Wi-Fi networks?
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Correct answer: A. IEEE 802.11
IEEE 802.11 is the standard that defines specifications for wireless local area networks (Wi-Fi). It covers the physical and data link layers for wireless communication. GSM and LTE are cellular mobile standards. IEEE 802.3 defines Ethernet for wired networks. EIA/TIA 568A is a standard for twisted-pair cabling and connector pinouts.
Why the other options are wrong
- B. GSM is a global standard for cellular mobile networks, not wireless local area networks.
- C. IEEE 802.3 specifies Ethernet for wired networks, not wireless Wi-Fi networks.
- D. LTE is a cellular mobile broadband standard, not a wireless LAN standard.
- E. EIA/TIA 568A defines wiring and connector standards for twisted-pair cabling, not W-i specifications.
Question 3
During the data encapsulation process, which OSI layer adds a header that contains MAC addressing information and a trailer used for error checking?
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Correct answer: D. Data Link
The Data Link layer (Layer 2) adds a header containing MAC (Media Access Control) addressing information and a trailer containing a Frame Check Sequence (FCS) or Cyclic Redundancy Check (CRC) for error detection. This creates a frame. The Network layer adds IP addresses, the Transport layer adds port numbers, and the Session layer manages logical connections.
Why the other options are wrong
- A. The Network layer adds IP addresses in its header but does not add a trailer for error checking.
- B. The Transport layer adds port numbers but does not add MAC addressing or erro-hecking trailers.
- C. The Session layer manages logical connections and dialogs between applications, not MAC addressing or error checking.
Question 4
Which protocol does an IPv6 host use to resolve the MAC address associated with a destination IPv6 address?
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Correct answer: A. Neighbor Discovery Protocol (NDP)
Neighbor Discovery Protocol (NDP) is the IPv6 equivalent of ARP and is used to resolve IPv6 addresses to MAC addresses. NDP uses ICMPv6 messages to perform this function. ARP is used for IPv4, not IPv6. CDP is a Cisco proprietary protocol for device discovery. DHCP is for address assignment, not address resolution.
Why the other options are wrong
- B. CDP (Cisco Discovery Protocol) is a proprietary protocol used to discover neighboring Cisco devices, not to resolve IPv6 addresses.
- C. DHCP is used for automatic IP address assignment and configuration, not for resolving addresses to MAC addresses.
- D. ARP (Address Resolution Protocol) is used for IPv4 address resolution, not IPv6.
Question 5
At which OSI layer is the data stream broken up into segments that include source and destination port numbers?
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Correct answer: A. Transport
The Transport layer (Layer 4) breaks the data stream into segments and adds source and destination port numbers in the header. This allows data to be directed to the correct application on the destination host. The Data Link layer works with frames and MAC addresses, the Network layer adds IP addresses, and the Session layer manages conversations between applications.
Why the other options are wrong
- B. The Data Link layer creates frames with MAC addresses, not segments with port numbers.
- C. The Session layer manages logical connections and dialogs but does not segment data or add port numbers.
- D. The Network layer adds IP addresses and creates packets, not segments with port numbers.
Question 6
Which protocol is used by IPv6-enabled hosts to perform automatic stateless address configuration?
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Correct answer: C. ICMPv6
ICMPv6 (Internet Control Message Protocol version 6) enables stateless address autoconfiguration (SLAAC) on IPv6 hosts. Through Router Advertisement messages, IPv6 hosts can automatically configure their own addresses without requiring a DHCP server. DHCPv6 provides stateful configuration but is not used for automatic stateless configuration. DNS resolves names, and TFTP transfers files.
Why the other options are wrong
- A. DHCPv6 provides stateful address configuration requiring a server, not automatic stateless configuration.
- B. DNS is used for name-to-IP address resolution, not for address configuration.
- D. TFTP is a file transfer protocol, not used for IPv6 address configuration.
Question 7
A host is given the IP address 172.16.100.25 and the subnet mask 255.255.252.0.
What is the CIDR notation for this address?
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Correct answer: B. 172.16.100.25 /22
CIDR notation counts the number of consecutive 1 bits in the subnet mask. In 255.255.252.0, the first two octets contribute 8 bits each and 252 in binary is 11111100, which adds 6 more network bits, for a total of 8 + 8 + 6 + 0 = 22. The address is therefore written 172.16.100.25 /22, leaving 10 host bits and a block size of 1024 addresses.
Why the other options are wrong
- A. /21 corresponds to the mask 255.255.248.0, where the third octet is 11111000.
- C. /23 corresponds to the mask 255.255.254.0, where the third octet is 11111110.
- D. /20 corresponds to the mask 255.255.240.0, where the third octet is 11110000.
Question 8
Which address is included in the 192.168.200.0/24 network?
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Correct answer: B. 192.168.200.13
The network 192.168.200.0/24 includes all addresses from 192.168.200.0 through 192.168.200.255. The /24 prefix means the entire fourth octet is variable. Option B (192.168.200.13) falls within this range. Options A, C, and D have different third octets (1, 199, and 201 respectively) and therefore do not belong to the 192.168.200.0/24 network.
Why the other options are wrong
- A. 192.168.1.13 has a different third octet (1 instead of 200) and is not in the 192.168.200.0/24 network.
- C. 192.168.199.13 has a different third octet (199 instead of 200) and is not in the 192.168.200.0/24 network.
- D. 192.168.201.13 has a different third octet (201 instead of 200) and is not in the 192.168.200.0/24 network.
Question 9
What is the most compressed valid format of the IPv6 address 2001:0db8:0000:0016:0000:001b:2000:0056?
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Correct answer: A. 2001:db8:0:16::1b:2000:56
Compression works in two steps: drop the leading zeros inside each hextet, then replace one run of consecutive all-zero hextets with a single double colon. Removing leading zeros gives 2001:db8:0:16:0:1b:2000:56, and because the double colon may appear only once and no hextet value may be altered, only one of the two single zero hextets can be replaced. Option A does exactly that, producing 2001:db8:0:16::1b:2000:56, which expands back to the original address.
Why the other options are wrong
- B. The double colon appears twice, which is invalid because the address could not be expanded unambiguously.
- C. Shortening 2000 to 2 removes trailing zeros, which is not allowed, so the hextet value is changed.
- D. This option both uses the double colon twice and truncates the 2000 hextet to 2.
Question 10
Which two statements are true about the IPv4 address of the default gateway configured on a host? (Choose two.)
Note: You will receive partial credit for each correct selection.
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Correct answer: C, D
C. The default gateway is the IPv4 address of the router interface connected to the same local network as the host. D. The same default gateway IPv4 address is configured on each host on the local network. The default gateway is the IPv4 address of the router interface that connects to the same local network segment as the host. This interface serves as the exit point for traffic destined outside the local network. All hosts on the same local network segment must be configured with the same default gateway address, which is the router's interface IP on that segment. This allows all hosts to forward non-local traffic through the same router interface.
Why the other options are wrong
- A. The default gateway does not need to be the first host address; it is typically a router interface address, which can be any usable address in the subnet.
- B. The default gateway is not the Loopback0 interface; Loopback interfaces are virtual and used for router management, not for forwarding host traffic.
- E. Hosts typically learn the default gateway through manual configuration or DHCP, not through router advertisement messages, which are used for IPv6 prefix discovery.
That was 10 of 75.
The full Cisco 100-150 CCST Networking pack has all 75 questions, each with the answer, the explanation and why the other options are wrong, plus a questions-only copy for timed runs. US$39, paid once, with free monthly updates and a pass-or-your-money-back guarantee.