Cisco 350-501 Practice Test 28
Question 270
For an original SPCOR service-provider engineering scenario, consider: BGP adjacency remains Active over a link on which OSPF is Full, but the engineer changes SPF costs instead of investigating BGP TCP port and source. Select TWO complementary steps: the targeted correction and its strongest prechange validation.
- Check: Inspect IPv6 link-local neighbors, interface instance and area data, OSPFv3 LSDB and installed IPv6 routes.
- Change: Choose the appropriate IPv6 transition and address-sharing model for subscriber connectivity, and test mapping state and application behavior end to end.
- Check: Compare per-protocol neighbor state, error messages, encapsulation, path reachability, authentication and interface counters.
- Treat a successful ping or another protocol's neighbor state as proof that all service provider routing adjacencies are healthy.
- Change: Diagnose the affected protocol's actual session prerequisites and advertisement scope before changing unrelated routing controls.
Explanation
Correct Answer
C:BGP establishes over TCP, OSPF uses protocol-specific IPv4 or IPv6 hellos and IS-IS exchanges Layer-2 link-local hellos; one protocol can work while another fails. Acceptance: Each intended adjacency reaches its required state and route advertisements are scoped correctly without unnecessary global routing changes.
E:BGP establishes over TCP, OSPF uses protocol-specific IPv4 or IPv6 hellos and IS-IS exchanges Layer-2 link-local hellos; one protocol can work while another fails. Evidence: Compare per-protocol neighbor state, error messages, encapsulation, path reachability, authentication and interface counters.
Incorrect Answers
A:Check: Inspect IPv6 link-local neighbors, interface instance and area data, OSPFv3 LSDB and installed IPv6 routes. BGP establishes over TCP, OSPF uses protocol-specific IPv4 or IPv6 hellos and IS-IS exchanges Layer-2 link-local hellos; one protocol can work while another fails.
B:Change: Choose the appropriate IPv6 transition and address-sharing model for subscriber connectivity, and test mapping state and application behavior end to end. BGP establishes over TCP, OSPF uses protocol-specific IPv4 or IPv6 hellos and IS-IS exchanges Layer-2 link-local hellos; one protocol can work while another fails.
D:For this select two assessment, the shortcut changes or bypasses the necessary routing, service or operational boundary rather than correcting it. BGP establishes over TCP, OSPF uses protocol-specific IPv4 or IPv6 hellos and IS-IS exchanges Layer-2 link-local hellos; one protocol can work while another fails.
Question 271
A service provider network engineer is reviewing this backbone or customer-service scenario: An IS-IS Level-2 neighbor stays Down while BGP routes appear through a separate interface, creating a false belief that all routing protocols share one neighbor state. A proposed shortcut is: Treat a successful ping or another protocol's neighbor state as proof that all service provider routing adjacencies are healthy. What should the service provider engineer recommend as the narrowly scoped correction? Select ONE best answer.
- Diagnose the affected protocol's actual session prerequisites and advertisement scope before changing unrelated routing controls.
- Treat a successful ping or another protocol's neighbor state as proof that all service provider routing adjacencies are healthy.
- Align peer AS, transport source, addressing, family activation and supported eBGP hop reachability for the actual topology.
- Enable compatible path diversity or BGP PIC mechanisms where supported and verify backup data-plane programming before a failure.
Explanation
Correct Answer
A:This targeted action addresses the observed service-provider control or forwarding gap without discarding necessary controls. Applied case: An IS-IS Level-2 neighbor stays Down while BGP routes appear through a separate interface, creating a false belief that all routing protocols share one neighbor state.
Incorrect Answers
B:BGP establishes over TCP, OSPF uses protocol-specific IPv4 or IPv6 hellos and IS-IS exchanges Layer-2 link-local hellos; one protocol can work while another fails. Applied case: An IS-IS Level-2 neighbor stays Down while BGP routes appear through a separate interface, creating a false belief that all routing protocols share one neighbor state.
C:Align peer AS, transport source, addressing, family activation and supported eBGP hop reachability for the actual topology. BGP establishes over TCP, OSPF uses protocol-specific IPv4 or IPv6 hellos and IS-IS exchanges Layer-2 link-local hellos; one protocol can work while another fails.
D:Enable compatible path diversity or BGP PIC mechanisms where supported and verify backup data-plane programming before a failure. BGP establishes over TCP, OSPF uses protocol-specific IPv4 or IPv6 hellos and IS-IS exchanges Layer-2 link-local hellos; one protocol can work while another fails.
Question 272
A Cisco service provider design review finds: An IS-IS Level-2 neighbor stays Down while BGP routes appear through a separate interface, creating a false belief that all routing protocols share one neighbor state. The team proposes: Diagnose the affected protocol's actual session prerequisites and advertisement scope before changing unrelated routing controls. Which engineering principle most strongly supports the recommended response? Select ONE best answer.
- BGP best-path selection considers local policy such as weight and local preference before several later tie breakers, including path length and MED context.
- BGP establishes over TCP, OSPF uses protocol-specific IPv4 or IPv6 hellos and IS-IS exchanges Layer-2 link-local hellos; one protocol can work while another fails.
- BFD detects data-path forwarding failure independently of slower routing hellos but extreme timer settings can create false failures.
- Graceful restart can retain forwarding with peer help during control recovery, while NSR replicates live session state on supported dual-control-plane systems.
Explanation
Correct Answer
B:Demonstrable success requires: Each intended adjacency reaches its required state and route advertisements are scoped correctly without unnecessary global routing changes. Applied case: An IS-IS Level-2 neighbor stays Down while BGP routes appear through a separate interface, creating a false belief that all routing protocols share one neighbor state.
Incorrect Answers
A:BGP best-path selection considers local policy such as weight and local preference before several later tie breakers, including path length and MED context. BGP establishes over TCP, OSPF uses protocol-specific IPv4 or IPv6 hellos and IS-IS exchanges Layer-2 link-local hellos; one protocol can work while another fails.
C:BFD detects data-path forwarding failure independently of slower routing hellos but extreme timer settings can create false failures. BGP establishes over TCP, OSPF uses protocol-specific IPv4 or IPv6 hellos and IS-IS exchanges Layer-2 link-local hellos; one protocol can work while another fails.
D:Graceful restart can retain forwarding with peer help during control recovery, while NSR replicates live session state on supported dual-control-plane systems. BGP establishes over TCP, OSPF uses protocol-specific IPv4 or IPv6 hellos and IS-IS exchanges Layer-2 link-local hellos; one protocol can work while another fails.
Question 273
The service provider operations team has not yet approved a change. Current evidence indicates: An IS-IS Level-2 neighbor stays Down while BGP routes appear through a separate interface, creating a false belief that all routing protocols share one neighbor state. Which evidence best tests the technical diagnosis before approving a disruptive change? Select ONE best answer.
- Trace a known client flow through DNS resolution, IPv4 or IPv6 encapsulation, translator bindings and return path with packet captures.
- Compare BFD session state, negotiated intervals, packet drops and routing convergence after controlled loss and benign congestion tests.
- Compare per-protocol neighbor state, error messages, encapsulation, path reachability, authentication and interface counters.
- Check route-reflector client relationships, originator and cluster attributes, BGP next-hop resolution and the RIB versus FIB.
Explanation
Correct Answer
C:BGP establishes over TCP, OSPF uses protocol-specific IPv4 or IPv6 hellos and IS-IS exchanges Layer-2 link-local hellos; one protocol can work while another fails. Confirm afterward that: Each intended adjacency reaches its required state and route advertisements are scoped correctly without unnecessary global routing changes.
Incorrect Answers
A:Trace a known client flow through DNS resolution, IPv4 or IPv6 encapsulation, translator bindings and return path with packet captures. BGP establishes over TCP, OSPF uses protocol-specific IPv4 or IPv6 hellos and IS-IS exchanges Layer-2 link-local hellos; one protocol can work while another fails.
B:Compare BFD session state, negotiated intervals, packet drops and routing convergence after controlled loss and benign congestion tests. BGP establishes over TCP, OSPF uses protocol-specific IPv4 or IPv6 hellos and IS-IS exchanges Layer-2 link-local hellos; one protocol can work while another fails.
D:Check route-reflector client relationships, originator and cluster attributes, BGP next-hop resolution and the RIB versus FIB. BGP establishes over TCP, OSPF uses protocol-specific IPv4 or IPv6 hellos and IS-IS exchanges Layer-2 link-local hellos; one protocol can work while another fails.
Question 274
A candidate correction has been tested and the platform team requires a post-change acceptance check. Original problem: An IS-IS Level-2 neighbor stays Down while BGP routes appear through a separate interface, creating a false belief that all routing protocols share one neighbor state. The carrier operations owner needs positive and negative tests showing existing customer services remain available. Which acceptance result demonstrates correct service provider forwarding and control behavior without disrupting authorized workflows? Select ONE best answer.
- Intended EBGP adjacencies establish securely and exchange only approved prefixes in the selected address family.
- Each intended adjacency reaches its required state and route advertisements are scoped correctly without unnecessary global routing changes.
- Expected neighbors reach the appropriate full adjacency state and exchange synchronized LSDB information without hidden MTU mismatches.
- Stub or normal areas receive only intended advertisements and no unreachable discontiguous summary is treated as valid service connectivity.
Explanation
Correct Answer
B:BGP establishes over TCP, OSPF uses protocol-specific IPv4 or IPv6 hellos and IS-IS exchanges Layer-2 link-local hellos; one protocol can work while another fails. The approved implementation step was: Diagnose the affected protocol's actual session prerequisites and advertisement scope before changing unrelated routing controls.
Incorrect Answers
A:Intended EBGP adjacencies establish securely and exchange only approved prefixes in the selected address family. BGP establishes over TCP, OSPF uses protocol-specific IPv4 or IPv6 hellos and IS-IS exchanges Layer-2 link-local hellos; one protocol can work while another fails.
C:Expected neighbors reach the appropriate full adjacency state and exchange synchronized LSDB information without hidden MTU mismatches. BGP establishes over TCP, OSPF uses protocol-specific IPv4 or IPv6 hellos and IS-IS exchanges Layer-2 link-local hellos; one protocol can work while another fails.
D:This option addresses a different service provider engineering topic (OSPF multiarea ABR area types and route summarization) rather than the documented Routing adjacency troubleshooting across multiple protocols decision.
Question 275
An implementation sign-off request identifies the following problem: An IS-IS Level-2 neighbor stays Down while BGP routes appear through a separate interface, creating a false belief that all routing protocols share one neighbor state. Which paired technical change and validation should close the implementation review? Select ONE best answer.
- Change: Diagnose the affected protocol's actual session prerequisites and advertisement scope before changing unrelated routing controls. Verify: Compare per-protocol neighbor state, error messages, encapsulation, path reachability, authentication and interface counters.
- Change: Match IS-IS level operation and interface parameters before expecting LSP exchange and route installation across a service provider core link. Verify: Inspect IS-IS neighbor state, hello capture, interface MTU and level configuration at both endpoints.
- Change: Apply documented BGP community or extended-community policies at the intended import or export point and verify resulting attribute propagation. Verify: Check received and advertised BGP attributes, applied route policy, peer documentation and resulting best path for a controlled test prefix.
- Change: Enable compatible path diversity or BGP PIC mechanisms where supported and verify backup data-plane programming before a failure. Verify: Inspect negotiated additional-path capability, backup path RIB and FIB entries and forwarding interruption during simulated failure.
Explanation
Correct Answer
A:BGP establishes over TCP, OSPF uses protocol-specific IPv4 or IPv6 hellos and IS-IS exchanges Layer-2 link-local hellos; one protocol can work while another fails. The change is successful only when: Each intended adjacency reaches its required state and route advertisements are scoped correctly without unnecessary global routing changes.
Incorrect Answers
B:Change: Match IS-IS level operation and interface parameters before expecting LSP exchange and route installation across a service provider core link. BGP establishes over TCP, OSPF uses protocol-specific IPv4 or IPv6 hellos and IS-IS exchanges Layer-2 link-local hellos; one protocol can work while another fails.
C:This option addresses a different service provider engineering topic (BGP route-policy communities and provider preference) rather than the documented Routing adjacency troubleshooting across multiple protocols decision.
D:Change: Enable compatible path diversity or BGP PIC mechanisms where supported and verify backup data-plane programming before a failure. BGP establishes over TCP, OSPF uses protocol-specific IPv4 or IPv6 hellos and IS-IS exchanges Layer-2 link-local hellos; one protocol can work while another fails.
Question 276
A service provider network engineer is reviewing this backbone or customer-service scenario: An IPv6-only subscriber must reach an IPv4-only service, but the provider deploys DNS64 alone with no translation path. A proposed shortcut is: Enable DNS64 alone and assume it rewrites every required IPv4 header without an actual translator. What should the service provider engineer recommend as the narrowly scoped correction? Select ONE best answer.
- Diagnose the affected protocol's actual session prerequisites and advertisement scope before changing unrelated routing controls.
- Align peer AS, transport source, addressing, family activation and supported eBGP hop reachability for the actual topology.
- Enable DNS64 alone and assume it rewrites every required IPv4 header without an actual translator.
- Choose the appropriate IPv6 transition and address-sharing model for subscriber connectivity, and test mapping state and application behavior end to end.
Explanation
Correct Answer
D:This targeted action addresses the observed service-provider control or forwarding gap without discarding necessary controls. Applied case: An IPv6-only subscriber must reach an IPv4-only service, but the provider deploys DNS64 alone with no translation path.
Incorrect Answers
A:Diagnose the affected protocol's actual session prerequisites and advertisement scope before changing unrelated routing controls. An IPv6-only subscriber must reach an IPv4-only service, but the provider deploys DNS64 alone with no translation path.
B:Align peer AS, transport source, addressing, family activation and supported eBGP hop reachability for the actual topology. An IPv6-only subscriber must reach an IPv4-only service, but the provider deploys DNS64 alone with no translation path.
C:NAT64 translates between IPv6 and IPv4 with suitable discovery, while DS-Lite tunnels subscriber IPv4 over IPv6 to a shared CGN function; MAP-T uses different translation rules. For this best change assessment, the shortcut changes or bypasses the necessary routing, service or operational boundary rather than correcting it.
Question 277
A Cisco service provider design review finds: An IPv6-only subscriber must reach an IPv4-only service, but the provider deploys DNS64 alone with no translation path. The team proposes: Choose the appropriate IPv6 transition and address-sharing model for subscriber connectivity, and test mapping state and application behavior end to end. Which engineering principle most strongly supports the recommended response? Select ONE best answer.
- NAT64 translates between IPv6 and IPv4 with suitable discovery, while DS-Lite tunnels subscriber IPv4 over IPv6 to a shared CGN function; MAP-T uses different translation rules.
- Graceful restart can retain forwarding with peer help during control recovery, while NSR replicates live session state on supported dual-control-plane systems.
- Route filtering is an ordered policy decision with platform-specific syntax and implicit outcomes; bad matching or direction can leak or drop routes.
- BGP best-path selection considers local policy such as weight and local preference before several later tie breakers, including path length and MED context.
Explanation
Correct Answer
A:Demonstrable success requires: Authorized IPv6 and shared-IPv4 applications work with correct port mappings, accountability and predictable failure handling. Applied case: An IPv6-only subscriber must reach an IPv4-only service, but the provider deploys DNS64 alone with no translation path.
Incorrect Answers
B:Graceful restart can retain forwarding with peer help during control recovery, while NSR replicates live session state on supported dual-control-plane systems. NAT64 translates between IPv6 and IPv4 with suitable discovery, while DS-Lite tunnels subscriber IPv4 over IPv6 to a shared CGN function; MAP-T uses different translation rules.
C:Route filtering is an ordered policy decision with platform-specific syntax and implicit outcomes; bad matching or direction can leak or drop routes. NAT64 translates between IPv6 and IPv4 with suitable discovery, while DS-Lite tunnels subscriber IPv4 over IPv6 to a shared CGN function; MAP-T uses different translation rules.
D:BGP best-path selection considers local policy such as weight and local preference before several later tie breakers, including path length and MED context. NAT64 translates between IPv6 and IPv4 with suitable discovery, while DS-Lite tunnels subscriber IPv4 over IPv6 to a shared CGN function; MAP-T uses different translation rules.
Question 278
The service provider operations team has not yet approved a change. Current evidence indicates: An IPv6-only subscriber must reach an IPv4-only service, but the provider deploys DNS64 alone with no translation path. Which evidence best tests the technical diagnosis before approving a disruptive change? Select ONE best answer.
- Trace a known client flow through DNS resolution, IPv4 or IPv6 encapsulation, translator bindings and return path with packet captures.
- Examine NET values, level adjacency state, LSP originator IDs and intended area boundaries on a two-area diagram.
- Inspect member actor and partner state, bundle hashing, counters and traffic distribution under several representative flows.
- Measure neighbor resets, stale route retention, forwarding counters and route processing after a planned RP switchover.
Explanation
Correct Answer
A:NAT64 translates between IPv6 and IPv4 with suitable discovery, while DS-Lite tunnels subscriber IPv4 over IPv6 to a shared CGN function; MAP-T uses different translation rules. Applied case: An IPv6-only subscriber must reach an IPv4-only service, but the provider deploys DNS64 alone with no translation path.
Incorrect Answers
B:Examine NET values, level adjacency state, LSP originator IDs and intended area boundaries on a two-area diagram. An IPv6-only subscriber must reach an IPv4-only service, but the provider deploys DNS64 alone with no translation path.
C:Inspect member actor and partner state, bundle hashing, counters and traffic distribution under several representative flows. An IPv6-only subscriber must reach an IPv4-only service, but the provider deploys DNS64 alone with no translation path.
D:Measure neighbor resets, stale route retention, forwarding counters and route processing after a planned RP switchover. NAT64 translates between IPv6 and IPv4 with suitable discovery, while DS-Lite tunnels subscriber IPv4 over IPv6 to a shared CGN function; MAP-T uses different translation rules.
Question 279
A candidate correction has been tested and the platform team requires a post-change acceptance check. Original problem: An IPv6-only subscriber must reach an IPv4-only service, but the provider deploys DNS64 alone with no translation path. The carrier operations owner needs positive and negative tests showing existing customer services remain available. Which acceptance result demonstrates correct service provider forwarding and control behavior without disrupting authorized workflows? Select ONE best answer.
- Authorized IPv6 and shared-IPv4 applications work with correct port mappings, accountability and predictable failure handling.
- The intended Level-1 or Level-2 adjacency forms and the routers exchange consistent link-state information without dropping required hello traffic.
- The preferred transit path wins for documented policy reasons without unexpected route filtering or next-hop failure.
- Only policy-matched routes change forwarding or advertisement behavior and customer communities have their documented effect.
Explanation
Correct Answer
A:NAT64 translates between IPv6 and IPv4 with suitable discovery, while DS-Lite tunnels subscriber IPv4 over IPv6 to a shared CGN function; MAP-T uses different translation rules. The result must be validated using the documented device, service or access context.
Incorrect Answers
B:The intended Level-1 or Level-2 adjacency forms and the routers exchange consistent link-state information without dropping required hello traffic. NAT64 translates between IPv6 and IPv4 with suitable discovery, while DS-Lite tunnels subscriber IPv4 over IPv6 to a shared CGN function; MAP-T uses different translation rules.
C:The preferred transit path wins for documented policy reasons without unexpected route filtering or next-hop failure. NAT64 translates between IPv6 and IPv4 with suitable discovery, while DS-Lite tunnels subscriber IPv4 over IPv6 to a shared CGN function; MAP-T uses different translation rules.
D:Only policy-matched routes change forwarding or advertisement behavior and customer communities have their documented effect. NAT64 translates between IPv6 and IPv4 with suitable discovery, while DS-Lite tunnels subscriber IPv4 over IPv6 to a shared CGN function; MAP-T uses different translation rules.
Question 280
For an original SPCOR service-provider engineering scenario, consider: An IPv6-only subscriber must reach an IPv4-only service, but the provider deploys DNS64 alone with no translation path. Select TWO complementary steps: the targeted correction and its strongest prechange validation.
- Check: Trace a known client flow through DNS resolution, IPv4 or IPv6 encapsulation, translator bindings and return path with packet captures.
- Check: Inspect IS-IS neighbor state, hello capture, interface MTU and level configuration at both endpoints.
- Change: Choose the appropriate IPv6 transition and address-sharing model for subscriber connectivity, and test mapping state and application behavior end to end.
- Change: Choose correct OSPF area behavior and summarization boundaries, confirming permitted external and interarea route propagation.
- Enable DNS64 alone and assume it rewrites every required IPv4 header without an actual translator.
Explanation
Correct Answer
A:NAT64 translates between IPv6 and IPv4 with suitable discovery, while DS-Lite tunnels subscriber IPv4 over IPv6 to a shared CGN function; MAP-T uses different translation rules. Required intervention: Choose the appropriate IPv6 transition and address-sharing model for subscriber connectivity, and test mapping state and application behavior end to end.
C:NAT64 translates between IPv6 and IPv4 with suitable discovery, while DS-Lite tunnels subscriber IPv4 over IPv6 to a shared CGN function; MAP-T uses different translation rules. Evidence: Trace a known client flow through DNS resolution, IPv4 or IPv6 encapsulation, translator bindings and return path with packet captures.
Incorrect Answers
B:Check: Inspect IS-IS neighbor state, hello capture, interface MTU and level configuration at both endpoints. NAT64 translates between IPv6 and IPv4 with suitable discovery, while DS-Lite tunnels subscriber IPv4 over IPv6 to a shared CGN function; MAP-T uses different translation rules.
D:Change: Choose correct OSPF area behavior and summarization boundaries, confirming permitted external and interarea route propagation. An IPv6-only subscriber must reach an IPv4-only service, but the provider deploys DNS64 alone with no translation path.
E:For this select two assessment, the shortcut changes or bypasses the necessary routing, service or operational boundary rather than correcting it. NAT64 translates between IPv6 and IPv4 with suitable discovery, while DS-Lite tunnels subscriber IPv4 over IPv6 to a shared CGN function; MAP-T uses different translation rules.
