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Question 250
A campus configures very aggressive BFD intervals on thousands of routed links and then sees intermittent neighbor flaps at peak CPU. Which observed result would most directly prove the design meets the intended goal?
- Both routed uplinks forward to the rest of campus and a link failure reroutes traffic without a campus STP event.
- Approved intersite traffic carries the expected segmentation context without undesired leakage.
- Uplink failure triggers the intended gateway takeover and remote application sessions recover.
- True failures are found promptly while healthy links no longer reset under ordinary control-plane load.
Explanation
Correct Answer
D:Tune BFD intervals and session scale to supported hardware and realistic detection requirements. Verify the resulting network behavior rather than relying only on the saved configuration.
Incorrect Answers
A:This observation relates to a different topology: A routed-access campus needs equal-cost forwarding to two distribution routers while keeping each VLAN local to one wiring closet. It does not verify the present outcome.
B:This observation relates to a different topology: An organization needs consistent segmentation across two SD-Access fabric sites connected by a routed MPLS service. It does not verify the present outcome.
C:This observation relates to a different topology: HSRP gateways remain reachable locally after their active router loses the only routed upstream uplink. It does not verify the present outcome.
Question 251
A regional site uses EIGRP neighbors with mismatched autonomous system numbers despite matching IP subnet and authentication. Which observed result would most directly prove the design meets the intended goal?
- The neighbors reach FULL and application packets traverse without fragmentation problems.
- The IPv6 client resolves and accesses the approved IPv4 service without adopting IPv4 on the client.
- Neighbors establish in the planned routing domain and exchange expected route prefixes.
- The hub forwards only to reachable site prefixes or intentionally documented summary ranges.
Explanation
Correct Answer
C:Align the intended EIGRP AS and verify the relevant interface network and authentication settings. Verify the resulting network behavior rather than relying only on the saved configuration.
Incorrect Answers
A:This observation relates to a different topology: Two OSPF neighbors on a routed core link are stuck in EXSTART/EXCHANGE and one endpoint uses an incompatible MTU. It does not verify the present outcome.
B:This observation relates to a different topology: A new IPv6-only client subnet must access a legacy IPv4-only web endpoint through an enterprise gateway. It does not verify the present outcome.
D:This observation relates to a different topology: Branches summarize their local EIGRP networks at a hub-facing boundary, but a detached subnet is included in the summary. It does not verify the present outcome.
Question 252
Two independent PIM-SM domains each use local rendezvous points but remote sources must be discovered across the domains. Which observed result would most directly prove the design meets the intended goal?
- Unit administrators can reach authorized nodes but are denied management of unrelated infrastructure.
- Only authorized operators can connect to device management while public services remain available.
- Sources registered in either domain become discoverable to intended remote receivers.
- An emergency administrator maintains workable session latency while backup transfer runs.
Explanation
Correct Answer
C:Evaluate supported MSDP-based source active exchange or a modern supported interdomain design. Verify the resulting network behavior rather than relying only on the saved configuration.
Incorrect Answers
A:This observation relates to a different topology: Two business units share one management VLAN with unrestricted access to each other's routers. It does not verify the present outcome.
B:This observation relates to a different topology: Remote branch routers are managed using the same public internet IP address that exposes a user web service. It does not verify the present outcome.
D:This observation relates to a different topology: A low-bandwidth remote management VPN carries huge nightly backup transfers that prevent emergency SSH access. It does not verify the present outcome.
Question 253
A customer needs private route separation for 12 branches over a shared provider backbone, not a single Ethernet broadcast domain. Which observed result would most directly prove the design meets the intended goal?
- Expected tagged traffic traverses the authorized EVC and unrelated tags are isolated.
- Authorized branch prefixes appear within the appropriate VPN and survive a PE failure as contracted.
- Each branch exchanges only authorized VPN routes while the provider backbone transports traffic without L2 extension.
- The approved VLAN service operates end to end without leaking unrelated hospital segments.
Explanation
Correct Answer
C:Choose a provider MPLS Layer 3 VPN with appropriate VRF route-target isolation and customer-to-provider routing. Verify the resulting network behavior rather than relying only on the saved configuration.
Incorrect Answers
A:This observation relates to a different topology: Two enterprise buildings use separate Metro Ethernet UNI ports, yet their operators assume the provider will preserve any configured customer VLAN ID. It does not verify the present outcome.
B:This observation relates to a different topology: A regional healthcare group wants routed site separation within a provider-managed private WAN without building its own full mesh of tunnels. It does not verify the present outcome.
D:This observation relates to a different topology: Two hospitals need their existing Ethernet VLANs extended across a provider circuit but their engineers incorrectly request a routed L3VPN. It does not verify the present outcome.
Question 254
A customer rents virtual machines from a provider and must patch their operating systems, but procurement classifies the service as SaaS. Which observed result would most directly prove the design meets the intended goal?
- An approved RESTCONF PATCH changes only the intended interface fields and a GET verifies effective state.
- Subscription updates decode into typed intended metrics and preserve their source paths.
- The responsibility matrix assigns OS patching and application security to the appropriate customer team.
- A controlled interface-down event arrives with correct device identity and event ordering after reconnection.
Explanation
Correct Answer
C:Classify the offering as IaaS and document customer responsibilities for guest OS, identities and workloads. Verify the resulting network behavior rather than relying only on the saved configuration.
Incorrect Answers
A:This observation relates to a different topology: A Python network tool must update structured interface configuration through web-style requests but the engineer chooses CLI scraping instead of a supported API. It does not verify the present outcome.
B:This observation relates to a different topology: A telemetry receiver supports gRPC but cannot decode the device's gNMI JSON_IETF path data and classifies every update as malformed. It does not verify the present outcome.
D:This observation relates to a different topology: A security operations service needs authoritative interface state changes, not a dashboard that replays stale telemetry after collector failure. It does not verify the present outcome.
Question 255
A branch router redistributes a static default to the campus IGP without approval, causing arbitrary sites to shift egress. Which observed result would most directly prove the design meets the intended goal?
- The corporate campus receives only the approved default from designated egress nodes.
- Clients retain gateway reachability after either distribution switch fails.
- Prefix changes within a campus no longer cause unnecessary global churn while remote packets use the proper border.
- Root bridge elections and forwarding paths match the documented campus topology.
Explanation
Correct Answer
A:Explicitly control default route origination and conditional advertisements at authorized borders. Verify the resulting network behavior rather than relying only on the saved configuration.
Incorrect Answers
B:This observation relates to a different topology: A building has two independent distribution switches but hosts use the physical IP of one switch as their default gateway. It does not verify the present outcome.
C:This observation relates to a different topology: Branch-specific prefix updates flood every campus router; a proposed aggregate crosses two distinct WAN egress sites. It does not verify the present outcome.
D:This observation relates to a different topology: A campus wants deterministic STP roots but all switches retain default bridge priorities. It does not verify the present outcome.
Question 256
An IS-IS backbone suffers topology oscillation because a marginal core link repeatedly flaps. Which observed result would most directly prove the design meets the intended goal?
- The neighbors reach FULL and application packets traverse without fragmentation problems.
- After repairing the link, LSP churn falls and traffic reconverges on stable intended paths.
- Other routers avoid using the overloaded node as unintended transit until it is ready.
- Both tenants resolve overlapping addresses within their own routing tables while approved intercompany services remain reachable.
Explanation
Correct Answer
B:Use appropriate convergence design, link health remediation, and scoped metric or fast-failure detection without masking a physical fault. Verify the resulting network behavior rather than relying only on the saved configuration.
Incorrect Answers
A:This observation relates to a different topology: Two OSPF neighbors on a routed core link are stuck in EXSTART/EXCHANGE and one endpoint uses an incompatible MTU. It does not verify the present outcome.
C:This observation relates to a different topology: The IS-IS backbone has a router in overload state after reboot and operators mistake it for an ordinary forwarding transit. It does not verify the present outcome.
D:This observation relates to a different topology: Two acquired companies both use 172.16.0.0/12; an immediate core merge would expose identical destination prefixes. It does not verify the present outcome.
Question 257
A multicast source is reachable through an interface other than the one receiving the packet, but the router still forwards it to all receivers. Which observed result would most directly prove the design meets the intended goal?
- Multicast forwarding resumes on the newly valid upstream with no persistent duplicates.
- Operators can reach device management after production routing is intentionally removed.
- Intended receivers across the routed boundary receive the source stream.
- Packets arriving on incorrect RPF interfaces are rejected and legitimate receiver traffic passes.
Explanation
Correct Answer
D:Verify correct Reverse Path Forwarding behavior and IGP unicast route alignment for multicast sources. Verify the resulting network behavior rather than relying only on the saved configuration.
Incorrect Answers
A:This observation relates to a different topology: The RPF interface changes after a unicast route failover, but the multicast router retains stale upstream join state. It does not verify the present outcome.
B:This observation relates to a different topology: A core router's production data plane fails, leaving SSH reachable only through the same failed core path. It does not verify the present outcome.
C:This observation relates to a different topology: A source sends multicast through one router but users join from another site and no multicast routing is configured between them. It does not verify the present outcome.
Question 258
Backup 5G is installed at a factory but its data plan and APN firewall rules block VPN establishment after primary fiber failure. Which observed result would most directly prove the design meets the intended goal?
- The required VPN tunnels and critical services establish over cellular during a failure exercise.
- Application sessions remain stable through short intermittent primary path disturbances.
- The site retains approved application reachability after losing one WAN edge or carrier path.
- Protected optical channels carry authorized client services with measured bit-error and failover performance.
Explanation
Correct Answer
A:Validate backup access, overlay establishment and route activation under simulated primary loss. Verify the resulting network behavior rather than relying only on the saved configuration.
Incorrect Answers
B:This observation relates to a different topology: A dual-carrier WAN design changes to backup but automatically switches back on every momentary primary heartbeat recovery. It does not verify the present outcome.
C:This observation relates to a different topology: A new SD-WAN site has a single edge appliance and single underlay yet is approved as redundant because controllers run in different data centers. It does not verify the present outcome.
D:This observation relates to a different topology: Several data centers need high-capacity optical transport over metropolitan dark fiber without converting each tenant VLAN to an IP tunnel. It does not verify the present outcome.
Question 259
A company assigns IPv6 /127 links between routers but a proposed monitoring tool treats each link as a /64 SLAAC user LAN. Which observed result would most directly prove the design meets the intended goal?
- Router adjacencies form on the /127 links while end hosts receive appropriate /64 router advertisements on user LANs.
- After repairing the link, LSP churn falls and traffic reconverges on stable intended paths.
- Clients reach the headquarters destination over the routed path using the approved office prefix.
- Observed inbound paths trend toward ISP B from representative external monitors without assuming universal control.
Explanation
Correct Answer
A:Keep /127 point-to-point addressing for supported router links and use separate /64 allocations for conventional endpoint segments. Verify the resulting network behavior rather than relying only on the saved configuration.
Incorrect Answers
B:This observation relates to a different topology: An IS-IS backbone suffers topology oscillation because a marginal core link repeatedly flaps. It does not verify the present outcome.
C:This observation relates to a different topology: A remote office assigns clients addresses from 169.254.0.0/16 and expects them to be reachable through a routed WAN. It does not verify the present outcome.
D:This observation relates to a different topology: A company wants most return traffic for its public prefix to enter ISP B rather than ISP A. It does not verify the present outcome.
Question 260
A campus wants deterministic STP roots but all switches retain default bridge priorities. Which observed result would most directly prove the design meets the intended goal?
- The corporate campus receives only the approved default from designated egress nodes.
- Root bridge elections and forwarding paths match the documented campus topology.
- The unintended default is absent from production campus RIBs while valid branch summaries propagate.
- Clients retain gateway reachability after either distribution switch fails.
Explanation
Correct Answer
B:Place primary and secondary STP root roles at the appropriate distribution devices for the planned VLAN sets. Verify the resulting network behavior rather than relying only on the saved configuration.
Incorrect Answers
A:This observation relates to a different topology: A branch router redistributes a static default to the campus IGP without approval, causing arbitrary sites to shift egress. It does not verify the present outcome.
C:This observation relates to a different topology: A regional core accepts all branch routes and one lab site leaks its test 0.0.0.0/0 default into the global table. It does not verify the present outcome.
D:This observation relates to a different topology: A building has two independent distribution switches but hosts use the physical IP of one switch as their default gateway. It does not verify the present outcome.
Designing Cisco Enterprise Networks (ENSLD) (300-420) Practice Tests
