Cisco Certified Support Technician (CCST) Networking 100-150 Practice Test 27
Question 260
Before approving the action, review: At the fictional Sunrise Payment Office before a planned system change, the team observes: An admin converts /27 to a mask of 255.255.255.0 and allocates too many clients to a tiny segment. During “Apply 255.255.255.224 and recalculate the subnet's network and broadcast boundaries.”, which precaution MOST specifically prevents a related risk?
- Do not assume a 100.70.x.x WAN address is independently public and accepts inbound internet connections.
- Do not treat 2001:db8:: documentation space as a routable production IPv6 allocation.
- Do not use a /24 mask with a documented /27 prefix length.
- Do not advertise RFC 1918 workstation addresses as globally routable internet prefixes.
Explanation
Correct Answer
C:Correct. This precaution prevents a second fault while applying “Apply 255.255.255.224 and recalculate the subnet's network and broadcast boundaries.” at the fictional Sunrise Payment Office. The required protection is “Do not use a /24 mask with a documented /27 prefix length.”; success still requires “The subnet calculator and manual bitmask agree on the 32-address block size.”.
Incorrect Answers
A:This caution is appropriate for a separate failure pattern: A guest Wi-Fi laptop shows 100.70.4.9 on the carrier-facing status page and the technician treats it as a customer-owned public IPv4 for inbound hosting. The principal adjacent risk here is controlled by “Do not use a /24 mask with a documented /27 prefix length.”.
B:This caution is appropriate for a separate failure pattern: An IPv6 endpoint is configured with 2001:db8:abcd:2::9/64 for a lab and the technician expects it to be a publicly assigned production Internet prefix. The principal adjacent risk here is controlled by “Do not use a /24 mask with a documented /27 prefix length.”.
D:This caution is appropriate for a separate failure pattern: A small-office PC uses 192.168.40.17 and a trainee proposes advertising it as a directly reachable address on the public internet. The principal adjacent risk here is controlled by “Do not use a /24 mask with a documented /27 prefix length.”.
Question 261
A technician reviews the following issue: At the fictional Westport Transit Depot in a technician onboarding review, the team observes: A workstation is configured as 172.16.9.34/23 but the operator assumes 172.16.9.0 is the network ID. Which action MOST directly resolves the reported issue?
- Keep the private prefix internally and arrange approved NAT or public address allocation at the network edge.
- Determine the network as 172.16.8.0 and broadcast as 172.16.9.255.
- Investigate the DHCP or static configuration path before relying on the link-local address for routed access.
- Use ::/0 with the appropriate IPv6 next hop in the IPv6 routing table.
Explanation
Correct Answer
B:Correct. In the fictional Westport Transit Depot case, The /23 mask 255.255.254.0 groups the third octet into pairs, placing 9 in network 172.16.8.0/23. The specified corrective action, “Determine the network as 172.16.8.0 and broadcast as 172.16.9.255.”, directly targets that condition. Evidence of resolution: Manual subnet calculation matches a trusted calculator for the /23 address.
Incorrect Answers
A:That action addresses a different network issue: A support analyst believes an internal 192.168.50.0/24 address can be made public solely by changing the router's default route. The present fictional Westport Transit Depot finding instead needs “Determine the network as 172.16.8.0 and broadcast as 172.16.9.255.”, verified by “Manual subnet calculation matches a trusted calculator for the /23 address.”.
C:That action addresses a different network issue: A receptionist reports 169.254.88.2 on a Windows laptop and the team tries to treat it as an ordinary assigned internet WAN address. The present fictional Westport Transit Depot finding instead needs “Determine the network as 172.16.8.0 and broadcast as 172.16.9.255.”, verified by “Manual subnet calculation matches a trusted calculator for the /23 address.”.
D:That action addresses a different network issue: A router carries an IPv6 default route and a trainee writes it as 0.0.0.0/0 in the IPv6 route table. The present fictional Westport Transit Depot finding instead needs “Determine the network as 172.16.8.0 and broadcast as 172.16.9.255.”, verified by “Manual subnet calculation matches a trusted calculator for the /23 address.”.
Question 262
An incident reviewer analyzes this observation: At the fictional Westport Transit Depot in a technician onboarding review, the team observes: A workstation is configured as 172.16.9.34/23 but the operator assumes 172.16.9.0 is the network ID. What is the MOST specific underlying cause?
- The /23 mask 255.255.254.0 groups the third octet into pairs, placing 9 in network 172.16.8.0/23.
- IPv6 fc00::/7 designates unique-local addressing, commonly represented by fd00::/8 prefixes.
- The RFC 1918 private range spans 172.16.0.0 through 172.31.255.255, including 172.20.14.8.
- 2001:db8::/32 is reserved for documentation examples rather than publicly routed production allocation.
Explanation
Correct Answer
A:Correct. This mechanism fits the observed network symptom at the fictional Westport Transit Depot: The /23 mask 255.255.254.0 groups the third octet into pairs, placing 9 in network 172.16.8.0/23. The corresponding remedy is “Determine the network as 172.16.8.0 and broadcast as 172.16.9.255.”. Confirmation: Manual subnet calculation matches a trusted calculator for the /23 address.
Incorrect Answers
B:That cause belongs to a different case: A student sees fd34:5:6::10 and labels it a global publicly reachable address merely because it is 128 bits long. The observed fictional Westport Transit Depot condition is specifically explained by “The /23 mask 255.255.254.0 groups the third octet into pairs, placing 9 in network 172.16.8.0/23.”.
C:That cause belongs to a different case: A branch device has 172.20.14.8 but a technician labels it public because every 172.x.x.x address is public. The observed fictional Westport Transit Depot condition is specifically explained by “The /23 mask 255.255.254.0 groups the third octet into pairs, placing 9 in network 172.16.8.0/23.”.
D:That cause belongs to a different case: An IPv6 endpoint is configured with 2001:db8:abcd:2::9/64 for a lab and the technician expects it to be a publicly assigned production Internet prefix. The observed fictional Westport Transit Depot condition is specifically explained by “The /23 mask 255.255.254.0 groups the third octet into pairs, placing 9 in network 172.16.8.0/23.”.
Question 263
After an approved correction, the support team reviews: At the fictional Westport Transit Depot in a technician onboarding review, the team observes: A workstation is configured as 172.16.9.34/23 but the operator assumes 172.16.9.0 is the network ID. The approved corrective action is: “Determine the network as 172.16.8.0 and broadcast as 172.16.9.255.” Which result BEST demonstrates success?
- The production IPv6 interface uses an authorized prefix and examples retain the documentation address.
- The route-and-NAT diagram treats the public DNS service differently from the local private host.
- The IPv6 forwarding table lists ::/0 and can select it for destinations without a more-specific route.
- Manual subnet calculation matches a trusted calculator for the /23 address.
Explanation
Correct Answer
D:Correct. This is the required observable acceptance evidence for “Determine the network as 172.16.8.0 and broadcast as 172.16.9.255.” at the fictional Westport Transit Depot. It demonstrates correction of the original cause: The /23 mask 255.255.254.0 groups the third octet into pairs, placing 9 in network 172.16.8.0/23.
Incorrect Answers
A:That result is evidence for a separate corrective action, “Keep 2001:db8:abcd:2::/64 in documentation and use a real assigned prefix for production.”. It does not establish the intended outcome “Manual subnet calculation matches a trusted calculator for the /23 address.” for the fictional Westport Transit Depot case.
B:That result is evidence for a separate corrective action, “Distinguish public and private source scopes and identify the required boundary translation.”. It does not establish the intended outcome “Manual subnet calculation matches a trusted calculator for the /23 address.” for the fictional Westport Transit Depot case.
C:That result is evidence for a separate corrective action, “Use ::/0 with the appropriate IPv6 next hop in the IPv6 routing table.”. It does not establish the intended outcome “Manual subnet calculation matches a trusted calculator for the /23 address.” for the fictional Westport Transit Depot case.
Question 264
Before approving the action, review: At the fictional Westport Transit Depot in a technician onboarding review, the team observes: A workstation is configured as 172.16.9.34/23 but the operator assumes 172.16.9.0 is the network ID. During “Determine the network as 172.16.8.0 and broadcast as 172.16.9.255.”, which precaution MOST specifically prevents a related risk?
- Do not invent a universal IPv6 broadcast address modeled on IPv4 .255.
- Do not replace a documented CIDR prefix with a historical classful default.
- Do not treat a /23 as though the third-octet mask were 255.
- Do not promise public reachability for RFC 1918 addresses merely from a route change.
Explanation
Correct Answer
C:Correct. This precaution prevents a second fault while applying “Determine the network as 172.16.8.0 and broadcast as 172.16.9.255.” at the fictional Westport Transit Depot. The required protection is “Do not treat a /23 as though the third-octet mask were 255.”; success still requires “Manual subnet calculation matches a trusted calculator for the /23 address.”.
Incorrect Answers
A:This caution is appropriate for a separate failure pattern: A technician expects IPv6 to send a subnet-wide broadcast address like 192.168.1.255 when contacting all local nodes. The principal adjacent risk here is controlled by “Do not treat a /23 as though the third-octet mask were 255.”.
B:This caution is appropriate for a separate failure pattern: A trainee is told an old Class C IPv4 label requires a /24 mask even though a configured interface explicitly uses /27. The principal adjacent risk here is controlled by “Do not treat a /23 as though the third-octet mask were 255.”.
D:This caution is appropriate for a separate failure pattern: A support analyst believes an internal 192.168.50.0/24 address can be made public solely by changing the router's default route. The principal adjacent risk here is controlled by “Do not treat a /23 as though the third-octet mask were 255.”.
Question 265
A technician reviews the following issue: At the fictional Cascade Science Lab while checking a service ticket, the team observes: An office assigns the same IPv4 address to a router interface and a server on one VLAN and the pair has intermittent reachability. Which action MOST directly resolves the reported issue?
- Explain the /64 split between network prefix and interface identifier for the example subnet.
- Assign separate available host addresses and confirm unique ARP mappings.
- Classify the fd34:5:6::10 address as ULA and distinguish it from global unicast.
- Use an assigned global unicast or properly routed address for off-link communication.
Explanation
Correct Answer
B:Correct. In the fictional Cascade Science Lab case, Duplicate IPv4 host addresses on the same broadcast segment can cause ARP conflicts and loss of stable delivery. The specified corrective action, “Assign separate available host addresses and confirm unique ARP mappings.”, directly targets that condition. Evidence of resolution: ARP and neighbor checks identify only one MAC for each intended IP after remediation.
Incorrect Answers
A:That action addresses a different network issue: A technician assumes an IPv6 /64 has a 64-bit address in total rather than a 128-bit address with a 64-bit prefix. The present fictional Cascade Science Lab finding instead needs “Assign separate available host addresses and confirm unique ARP mappings.”, verified by “ARP and neighbor checks identify only one MAC for each intended IP after remediation.”.
C:That action addresses a different network issue: A student sees fd34:5:6::10 and labels it a global publicly reachable address merely because it is 128 bits long. The present fictional Cascade Science Lab finding instead needs “Assign separate available host addresses and confirm unique ARP mappings.”, verified by “ARP and neighbor checks identify only one MAC for each intended IP after remediation.”.
D:That action addresses a different network issue: A workstation shows fe80::7a4b on its IPv6 interface and a technician tries to route it as a globally reachable internet destination. The present fictional Cascade Science Lab finding instead needs “Assign separate available host addresses and confirm unique ARP mappings.”, verified by “ARP and neighbor checks identify only one MAC for each intended IP after remediation.”.
Question 266
An incident reviewer analyzes this observation: At the fictional Cascade Science Lab while checking a service ticket, the team observes: An office assigns the same IPv4 address to a router interface and a server on one VLAN and the pair has intermittent reachability. What is the MOST specific underlying cause?
- Duplicate IPv4 host addresses on the same broadcast segment can cause ARP conflicts and loss of stable delivery.
- ff00::/8 identifies IPv6 multicast addresses, and ff02::1 targets all nodes on the local link.
- The 192.168.0.0/16 block is RFC 1918 private addressing and is not routed as an ordinary public destination.
- IPv6 :: compression represents a contiguous run of zero 16-bit groups and may appear only once in one address.
Explanation
Correct Answer
A:Correct. This mechanism fits the observed network symptom at the fictional Cascade Science Lab: Duplicate IPv4 host addresses on the same broadcast segment can cause ARP conflicts and loss of stable delivery. The corresponding remedy is “Assign separate available host addresses and confirm unique ARP mappings.”. Confirmation: ARP and neighbor checks identify only one MAC for each intended IP after remediation.
Incorrect Answers
B:That cause belongs to a different case: A device sends a packet to ff02::1 and the support note calls it a single host's IPv6 unicast address. The observed fictional Cascade Science Lab condition is specifically explained by “Duplicate IPv4 host addresses on the same broadcast segment can cause ARP conflicts and loss of stable delivery.”.
C:That cause belongs to a different case: A small-office PC uses 192.168.40.17 and a trainee proposes advertising it as a directly reachable address on the public internet. The observed fictional Cascade Science Lab condition is specifically explained by “Duplicate IPv4 host addresses on the same broadcast segment can cause ARP conflicts and loss of stable delivery.”.
D:That cause belongs to a different case: A student expands 2001:db8::5 into an address with two separate :: compression markers and too many hextets. The observed fictional Cascade Science Lab condition is specifically explained by “Duplicate IPv4 host addresses on the same broadcast segment can cause ARP conflicts and loss of stable delivery.”.
Question 267
After an approved correction, the support team reviews: At the fictional Cascade Science Lab while checking a service ticket, the team observes: An office assigns the same IPv4 address to a router interface and a server on one VLAN and the pair has intermittent reachability. The approved corrective action is: “Assign separate available host addresses and confirm unique ARP mappings.” Which result BEST demonstrates success?
- An external site sees the approved edge public source while the workstation retains its private address.
- The computed network and host range follow /27, not an assumed classful /24.
- The link-local address remains local while the global address reaches a remote IPv6 host.
- ARP and neighbor checks identify only one MAC for each intended IP after remediation.
Explanation
Correct Answer
D:Correct. This is the required observable acceptance evidence for “Assign separate available host addresses and confirm unique ARP mappings.” at the fictional Cascade Science Lab. It demonstrates correction of the original cause: Duplicate IPv4 host addresses on the same broadcast segment can cause ARP conflicts and loss of stable delivery.
Incorrect Answers
A:That result is evidence for a separate corrective action, “Keep the private prefix internally and arrange approved NAT or public address allocation at the network edge.”. It does not establish the intended outcome “ARP and neighbor checks identify only one MAC for each intended IP after remediation.” for the fictional Cascade Science Lab case.
B:That result is evidence for a separate corrective action, “Use the configured /27 prefix and corresponding mask for the subnet calculation.”. It does not establish the intended outcome “ARP and neighbor checks identify only one MAC for each intended IP after remediation.” for the fictional Cascade Science Lab case.
C:That result is evidence for a separate corrective action, “Use an assigned global unicast or properly routed address for off-link communication.”. It does not establish the intended outcome “ARP and neighbor checks identify only one MAC for each intended IP after remediation.” for the fictional Cascade Science Lab case.
Question 268
Before approving the action, review: At the fictional Cascade Science Lab while checking a service ticket, the team observes: An office assigns the same IPv4 address to a router interface and a server on one VLAN and the pair has intermittent reachability. During “Assign separate available host addresses and confirm unique ARP mappings.”, which precaution MOST specifically prevents a related risk?
- Do not advertise a fe80:: link-local address as an ordinary global internet route.
- Do not confuse the client's private source address with the public source observed after PAT.
- Do not assign duplicate IPv4 host addresses inside one broadcast domain.
- Do not assign an ff02:: multicast address as an ordinary single-host unicast interface.
Explanation
Correct Answer
C:Correct. This precaution prevents a second fault while applying “Assign separate available host addresses and confirm unique ARP mappings.” at the fictional Cascade Science Lab. The required protection is “Do not assign duplicate IPv4 host addresses inside one broadcast domain.”; success still requires “ARP and neighbor checks identify only one MAC for each intended IP after remediation.”.
Incorrect Answers
A:This caution is appropriate for a separate failure pattern: A workstation shows fe80::7a4b on its IPv6 interface and a technician tries to route it as a globally reachable internet destination. The principal adjacent risk here is controlled by “Do not assign duplicate IPv4 host addresses inside one broadcast domain.”.
B:This caution is appropriate for a separate failure pattern: A shared office connects many private IPv4 clients to the internet but expects each to consume a separate public address despite a single ISP-facing IPv4. The principal adjacent risk here is controlled by “Do not assign duplicate IPv4 host addresses inside one broadcast domain.”.
D:This caution is appropriate for a separate failure pattern: A device sends a packet to ff02::1 and the support note calls it a single host's IPv6 unicast address. The principal adjacent risk here is controlled by “Do not assign duplicate IPv4 host addresses inside one broadcast domain.”.
Question 269
A technician reviews the following issue: At the fictional Seabrook Bakery after a user reports a recurring problem, the team observes: A remote endpoint uses 192.168.60.18/26 with gateway 192.168.60.126 and cannot leave its LAN. Which action MOST directly resolves the reported issue?
- Identify the appropriate link-local IPv6 multicast group for the intended discovery or group message.
- Configure a default gateway address within the workstation's 192.168.60.0/26 subnet.
- Apply the correct 172.16.0.0/12 private address boundary to the branch inventory.
- Keep the workstation on its private LAN and use approved address translation or a secure remote-access design at the edge.
Explanation
Correct Answer
B:Correct. In the fictional Seabrook Bakery case, In a /26, .18 is in 192.168.60.0–.63 while .126 is in a different subnet .64–.127. The specified corrective action, “Configure a default gateway address within the workstation's 192.168.60.0/26 subnet.”, directly targets that condition. Evidence of resolution: The endpoint can ARP for the gateway and reach an off-subnet test host.
Incorrect Answers
A:That action addresses a different network issue: A technician expects IPv6 to send a subnet-wide broadcast address like 192.168.1.255 when contacting all local nodes. The present fictional Seabrook Bakery finding instead needs “Configure a default gateway address within the workstation's 192.168.60.0/26 subnet.”, verified by “The endpoint can ARP for the gateway and reach an off-subnet test host.”.
C:That action addresses a different network issue: A branch device has 172.20.14.8 but a technician labels it public because every 172.x.x.x address is public. The present fictional Seabrook Bakery finding instead needs “Configure a default gateway address within the workstation's 192.168.60.0/26 subnet.”, verified by “The endpoint can ARP for the gateway and reach an off-subnet test host.”.
D:That action addresses a different network issue: A small-office PC uses 192.168.40.17 and a trainee proposes advertising it as a directly reachable address on the public internet. The present fictional Seabrook Bakery finding instead needs “Configure a default gateway address within the workstation's 192.168.60.0/26 subnet.”, verified by “The endpoint can ARP for the gateway and reach an off-subnet test host.”.
Question 270
An incident reviewer analyzes this observation: At the fictional Seabrook Bakery after a user reports a recurring problem, the team observes: A remote endpoint uses 192.168.60.18/26 with gateway 192.168.60.126 and cannot leave its LAN. What is the MOST specific underlying cause?
- In a /26, .18 is in 192.168.60.0–.63 while .126 is in a different subnet .64–.127.
- The 192.168.0.0/16 block is RFC 1918 private addressing and is not routed as an ordinary public destination.
- 10.0.0.0/8 is the private IPv4 block regardless of the apparent decimal value of its octets.
- IPv6 does not use IPv4-style broadcast; multicast serves applicable group communication roles.
Explanation
Correct Answer
A:Correct. This mechanism fits the observed network symptom at the fictional Seabrook Bakery: In a /26, .18 is in 192.168.60.0–.63 while .126 is in a different subnet .64–.127. The corresponding remedy is “Configure a default gateway address within the workstation's 192.168.60.0/26 subnet.”. Confirmation: The endpoint can ARP for the gateway and reach an off-subnet test host.
Incorrect Answers
B:That cause belongs to a different case: A small-office PC uses 192.168.40.17 and a trainee proposes advertising it as a directly reachable address on the public internet. The observed fictional Seabrook Bakery condition is specifically explained by “In a /26, .18 is in 192.168.60.0–.63 while .126 is in a different subnet .64–.127.”.
C:That cause belongs to a different case: An administrator sees 10.42.7.18 in a lab and calls it a globally assigned public IPv4 address because its first octet is small. The observed fictional Seabrook Bakery condition is specifically explained by “In a /26, .18 is in 192.168.60.0–.63 while .126 is in a different subnet .64–.127.”.
D:That cause belongs to a different case: A technician expects IPv6 to send a subnet-wide broadcast address like 192.168.1.255 when contacting all local nodes. The observed fictional Seabrook Bakery condition is specifically explained by “In a /26, .18 is in 192.168.60.0–.63 while .126 is in a different subnet .64–.127.”.