Cisco 350-501 Practice Test 27
Question 260
For an original SPCOR service-provider engineering scenario, consider: A migration redistributes every customer BGP route into the IGP and overwhelms core LSDB memory while leaking unrelated service prefixes. Select TWO complementary steps: the targeted correction and its strongest prechange validation.
- Check: Trace sample source routes, redistribution policy hits, tags, LSDB or LSP size and resulting RIB changes across both boundaries.
- Change: Restrict redistribution using explicit route policy and tags, and maintain a scalable separation of service prefixes from core IGP reachability.
- Check: Check route-reflector client relationships, originator and cluster attributes, BGP next-hop resolution and the RIB versus FIB.
- Change: Assign unique IS-IS system IDs and consistent area identifiers for Level-1 adjacency, with proper Level-2 reachability across areas.
- Redistribute the entire global BGP table into OSPF or IS-IS and rely on implicit loop protection.
Explanation
Correct Answer
A:Redistribution changes protocol scope and metrics; uncontrolled mutual redistribution can create loops and excessive IGP state. Acceptance: Only planned prefixes cross the protocol boundary once and core convergence remains stable under service-route churn.
B:Redistribution changes protocol scope and metrics; uncontrolled mutual redistribution can create loops and excessive IGP state. Evidence: Trace sample source routes, redistribution policy hits, tags, LSDB or LSP size and resulting RIB changes across both boundaries.
Incorrect Answers
C:Check: Check route-reflector client relationships, originator and cluster attributes, BGP next-hop resolution and the RIB versus FIB. Redistribution changes protocol scope and metrics; uncontrolled mutual redistribution can create loops and excessive IGP state.
D:Change: Assign unique IS-IS system IDs and consistent area identifiers for Level-1 adjacency, with proper Level-2 reachability across areas. Redistribution changes protocol scope and metrics; uncontrolled mutual redistribution can create loops and excessive IGP state.
E:For this select two assessment, the shortcut changes or bypasses the necessary routing, service or operational boundary rather than correcting it. Redistribution changes protocol scope and metrics; uncontrolled mutual redistribution can create loops and excessive IGP state.
Question 261
A service provider network engineer is reviewing this backbone or customer-service scenario: Two routing domains exchange redistributions in both directions without tags and routes continually reappear with incorrect administrative ownership. A proposed shortcut is: Redistribute the entire global BGP table into OSPF or IS-IS and rely on implicit loop protection. What should the service provider engineer recommend as the narrowly scoped correction? Select ONE best answer.
- Redistribute the entire global BGP table into OSPF or IS-IS and rely on implicit loop protection.
- Restrict redistribution using explicit route policy and tags, and maintain a scalable separation of service prefixes from core IGP reachability.
- Use the platform's supported policy language, explicit prefix sets and match sequencing to permit only intended routes and apply actions at the correct direction.
- Choose correct OSPF area behavior and summarization boundaries, confirming permitted external and interarea route propagation.
Explanation
Correct Answer
B:This targeted action addresses the observed service-provider control or forwarding gap without discarding necessary controls. Applied case: Two routing domains exchange redistributions in both directions without tags and routes continually reappear with incorrect administrative ownership.
Incorrect Answers
A:Redistribution changes protocol scope and metrics; uncontrolled mutual redistribution can create loops and excessive IGP state. Applied case: Two routing domains exchange redistributions in both directions without tags and routes continually reappear with incorrect administrative ownership.
C:Use the platform's supported policy language, explicit prefix sets and match sequencing to permit only intended routes and apply actions at the correct direction. Redistribution changes protocol scope and metrics; uncontrolled mutual redistribution can create loops and excessive IGP state.
D:Choose correct OSPF area behavior and summarization boundaries, confirming permitted external and interarea route propagation. Redistribution changes protocol scope and metrics; uncontrolled mutual redistribution can create loops and excessive IGP state.
Question 262
A Cisco service provider design review finds: Two routing domains exchange redistributions in both directions without tags and routes continually reappear with incorrect administrative ownership. The team proposes: Restrict redistribution using explicit route policy and tags, and maintain a scalable separation of service prefixes from core IGP reachability. Which engineering principle most strongly supports the recommended response? Select ONE best answer.
- Graceful restart can retain forwarding with peer help during control recovery, while NSR replicates live session state on supported dual-control-plane systems.
- OSPF SPF evaluates cumulative link costs, including configured interface cost and supported reference-bandwidth scaling, not geographic distance.
- Redistribution changes protocol scope and metrics; uncontrolled mutual redistribution can create loops and excessive IGP state.
- IS-IS NET encodes an area and unique system identifier; Level-1 flooding is area scoped while Level-2 connects interarea backbone reachability.
Explanation
Correct Answer
C:Relevant validation before approval: Trace sample source routes, redistribution policy hits, tags, LSDB or LSP size and resulting RIB changes across both boundaries. Applied case: Two routing domains exchange redistributions in both directions without tags and routes continually reappear with incorrect administrative ownership.
Incorrect Answers
A:Graceful restart can retain forwarding with peer help during control recovery, while NSR replicates live session state on supported dual-control-plane systems. Redistribution changes protocol scope and metrics; uncontrolled mutual redistribution can create loops and excessive IGP state.
B:OSPF SPF evaluates cumulative link costs, including configured interface cost and supported reference-bandwidth scaling, not geographic distance. Redistribution changes protocol scope and metrics; uncontrolled mutual redistribution can create loops and excessive IGP state.
D:IS-IS NET encodes an area and unique system identifier; Level-1 flooding is area scoped while Level-2 connects interarea backbone reachability. Redistribution changes protocol scope and metrics; uncontrolled mutual redistribution can create loops and excessive IGP state.
Question 263
The service provider operations team has not yet approved a change. Current evidence indicates: Two routing domains exchange redistributions in both directions without tags and routes continually reappear with incorrect administrative ownership. Which evidence best tests the technical diagnosis before approving a disruptive change? Select ONE best answer.
- Compare per-protocol neighbor state, error messages, encapsulation, path reachability, authentication and interface counters.
- Compare BFD session state, negotiated intervals, packet drops and routing convergence after controlled loss and benign congestion tests.
- Inspect IPv6 link-local neighbors, interface instance and area data, OSPFv3 LSDB and installed IPv6 routes.
- Trace sample source routes, redistribution policy hits, tags, LSDB or LSP size and resulting RIB changes across both boundaries.
Explanation
Correct Answer
D:Redistribution changes protocol scope and metrics; uncontrolled mutual redistribution can create loops and excessive IGP state. Confirm afterward that: Only planned prefixes cross the protocol boundary once and core convergence remains stable under service-route churn.
Incorrect Answers
A:Compare per-protocol neighbor state, error messages, encapsulation, path reachability, authentication and interface counters. Two routing domains exchange redistributions in both directions without tags and routes continually reappear with incorrect administrative ownership.
B:Compare BFD session state, negotiated intervals, packet drops and routing convergence after controlled loss and benign congestion tests. Redistribution changes protocol scope and metrics; uncontrolled mutual redistribution can create loops and excessive IGP state.
C:Inspect IPv6 link-local neighbors, interface instance and area data, OSPFv3 LSDB and installed IPv6 routes. Two routing domains exchange redistributions in both directions without tags and routes continually reappear with incorrect administrative ownership.
Question 264
A candidate correction has been tested and the platform team requires a post-change acceptance check. Original problem: Two routing domains exchange redistributions in both directions without tags and routes continually reappear with incorrect administrative ownership. 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.
- Only planned prefixes cross the protocol boundary once and core convergence remains stable under service-route churn.
- Failure recovery stays within service limits and no stale unvalidated forwarding state persists beyond documented timers.
- The intended Level-1 or Level-2 adjacency forms and the routers exchange consistent link-state information without dropping required hello traffic.
- Each intended adjacency reaches its required state and route advertisements are scoped correctly without unnecessary global routing changes.
Explanation
Correct Answer
A:Redistribution changes protocol scope and metrics; uncontrolled mutual redistribution can create loops and excessive IGP state. The approved implementation step was: Restrict redistribution using explicit route policy and tags, and maintain a scalable separation of service prefixes from core IGP reachability.
Incorrect Answers
B:Failure recovery stays within service limits and no stale unvalidated forwarding state persists beyond documented timers. Redistribution changes protocol scope and metrics; uncontrolled mutual redistribution can create loops and excessive IGP state.
C:The intended Level-1 or Level-2 adjacency forms and the routers exchange consistent link-state information without dropping required hello traffic. Redistribution changes protocol scope and metrics; uncontrolled mutual redistribution can create loops and excessive IGP state.
D:Each intended adjacency reaches its required state and route advertisements are scoped correctly without unnecessary global routing changes. Redistribution changes protocol scope and metrics; uncontrolled mutual redistribution can create loops and excessive IGP state.
Question 265
An implementation sign-off request identifies the following problem: Two routing domains exchange redistributions in both directions without tags and routes continually reappear with incorrect administrative ownership. Which paired technical change and validation should close the implementation review? Select ONE best answer.
- Change: Restrict redistribution using explicit route policy and tags, and maintain a scalable separation of service prefixes from core IGP reachability. Verify: Trace sample source routes, redistribution policy hits, tags, LSDB or LSP size and resulting RIB changes across both boundaries.
- Change: Align peer AS, transport source, addressing, family activation and supported eBGP hop reachability for the actual topology. Verify: Inspect BGP neighbor transport state, local and remote AS, update source, TCP reachability and IPv4 or IPv6 address-family activation.
- Change: Choose the appropriate IPv6 transition and address-sharing model for subscriber connectivity, and test mapping state and application behavior end to end. Verify: Trace a known client flow through DNS resolution, IPv4 or IPv6 encapsulation, translator bindings and return path with packet captures.
- Change: Deploy route reflection with deliberate client and cluster design and preserve IGP reachability to advertised BGP next hops. Verify: Check route-reflector client relationships, originator and cluster attributes, BGP next-hop resolution and the RIB versus FIB.
Explanation
Correct Answer
A:Redistribution changes protocol scope and metrics; uncontrolled mutual redistribution can create loops and excessive IGP state. The change is successful only when: Only planned prefixes cross the protocol boundary once and core convergence remains stable under service-route churn.
Incorrect Answers
B:Change: Align peer AS, transport source, addressing, family activation and supported eBGP hop reachability for the actual topology. Redistribution changes protocol scope and metrics; uncontrolled mutual redistribution can create loops and excessive IGP state.
C:Change: Choose the appropriate IPv6 transition and address-sharing model for subscriber connectivity, and test mapping state and application behavior end to end. Redistribution changes protocol scope and metrics; uncontrolled mutual redistribution can create loops and excessive IGP state.
D:Change: Deploy route reflection with deliberate client and cluster design and preserve IGP reachability to advertised BGP next hops. Redistribution changes protocol scope and metrics; uncontrolled mutual redistribution can create loops and excessive IGP state.
Question 266
A service provider network engineer is reviewing this backbone or customer-service scenario: 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. 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.
- Troubleshoot OSPF network type, area, neighbor timers, authentication and database-exchange parameters before modifying routing advertisements.
- Select single- or multi-topology IS-IS according to dual-stack forwarding requirements and verify both address-family reachability and advertised topology data.
- 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.
Explanation
Correct Answer
C:This targeted action addresses the observed service-provider control or forwarding gap without discarding necessary controls. Applied case: 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.
Incorrect Answers
A:Troubleshoot OSPF network type, area, neighbor timers, authentication and database-exchange parameters before modifying routing advertisements. 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:Select single- or multi-topology IS-IS according to dual-stack forwarding requirements and verify both address-family reachability and advertised topology data. 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: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. For this best change assessment, the shortcut changes or bypasses the necessary routing, service or operational boundary rather than correcting it.
Question 267
A Cisco service provider design review finds: 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. 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 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.
- MED influences comparisons under specific BGP decision contexts, and AS_PATH prepending is advisory because remote networks may apply their own preferences.
- 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.
- IS-IS adjacencies use link-local protocol hellos and compatible level, circuit and network settings; IP reachability alone does not create a neighbor.
Explanation
Correct Answer
A:Demonstrable success requires: Each intended adjacency reaches its required state and route advertisements are scoped correctly without unnecessary global routing changes. Applied case: 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.
Incorrect Answers
B:This option addresses a different service provider engineering topic (BGP MED AS_PATH prepending and ingress steering) rather than the documented Routing adjacency troubleshooting across multiple protocols decision.
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. 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:IS-IS adjacencies use link-local protocol hellos and compatible level, circuit and network settings; IP reachability alone does not create a neighbor. 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 268
The service provider operations team has not yet approved a change. Current evidence indicates: 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. Which evidence best tests the technical diagnosis before approving a disruptive change? Select ONE best answer.
- Check neighbor state transitions, interface MTU, hello and dead intervals, area type and network type on both peers.
- Record each link cost and LSDB view, calculate expected shortest paths and compare route changes during shut and no-shut tests.
- Inspect IPv6 link-local neighbors, interface instance and area data, OSPFv3 LSDB and installed IPv6 routes.
- Compare per-protocol neighbor state, error messages, encapsulation, path reachability, authentication and interface counters.
Explanation
Correct Answer
D: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: 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.
Incorrect Answers
A:Check neighbor state transitions, interface MTU, hello and dead intervals, area type and network type on both peers. 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:This option addresses a different service provider engineering topic (OSPF route cost and convergence after link changes) rather than the documented Routing adjacency troubleshooting across multiple protocols decision.
C: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.
Question 269
A candidate correction has been tested and the platform team requires a post-change acceptance check. Original problem: 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. 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.
- Failure recovery stays within service limits and no stale unvalidated forwarding state persists beyond documented timers.
- The preferred transit path wins for documented policy reasons without unexpected route filtering or next-hop failure.
- Each intended adjacency reaches its required state and route advertisements are scoped correctly without unnecessary global routing changes.
- Both address families receive valid advertised next hops for the chosen topology mode and failures are diagnosed per family.
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. The result must be validated using the documented device, service or access context.
Incorrect Answers
A:Failure recovery stays within service limits and no stale unvalidated forwarding state persists beyond documented timers. 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:The preferred transit path wins for documented policy reasons without unexpected route filtering or next-hop 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.
D:Both address families receive valid advertised next hops for the chosen topology mode and failures are diagnosed per 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.
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.
