Cisco 350-501 Practice Test 26
Question 250
For an original SPCOR service-provider engineering scenario, consider: An IOS XR route-policy is written like an IOS XE route-map and never passes the intended set of customer prefixes. Select TWO complementary steps: the targeted correction and its strongest prechange validation.
- Check: Evaluate a test table with allowed, denied and boundary prefixes against actual show-policy and BGP advertised-routes evidence.
- Change: 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.
- Copy a route map verbatim into IOS XR policy syntax and assume it preserves implicit deny and pass behavior.
- Check: Compare area LSDB LSA types, ABR summaries, default injection and actual endpoint reachability for inside and outside addresses.
- Change: Troubleshoot OSPF network type, area, neighbor timers, authentication and database-exchange parameters before modifying routing advertisements.
Explanation
Correct Answer
A:Route filtering is an ordered policy decision with platform-specific syntax and implicit outcomes; bad matching or direction can leak or drop routes. Required intervention: 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.
B:Route filtering is an ordered policy decision with platform-specific syntax and implicit outcomes; bad matching or direction can leak or drop routes. Evidence: Evaluate a test table with allowed, denied and boundary prefixes against actual show-policy and BGP advertised-routes evidence.
Incorrect Answers
C:For this select two assessment, the shortcut changes or bypasses the necessary routing, service or operational boundary rather than correcting it. Route filtering is an ordered policy decision with platform-specific syntax and implicit outcomes; bad matching or direction can leak or drop routes.
D:Check: Compare area LSDB LSA types, ABR summaries, default injection and actual endpoint reachability for inside and outside addresses. Route filtering is an ordered policy decision with platform-specific syntax and implicit outcomes; bad matching or direction can leak or drop routes.
E:Change: Troubleshoot OSPF network type, area, neighbor timers, authentication and database-exchange parameters before modifying routing advertisements. Route filtering is an ordered policy decision with platform-specific syntax and implicit outcomes; bad matching or direction can leak or drop routes.
Question 251
A service provider network engineer is reviewing this backbone or customer-service scenario: A provider's import filter matches all routes because a broad prefix set is evaluated before the more specific deny policy for leaked routes. A proposed shortcut is: Copy a route map verbatim into IOS XR policy syntax and assume it preserves implicit deny and pass behavior. What should the service provider engineer recommend as the narrowly scoped correction? Select ONE best answer.
- Verify OSPFv3 interface activation, matching area and instance settings and IPv6 address-family route advertisement before expecting end-to-end forwarding.
- Assign unique IS-IS system IDs and consistent area identifiers for Level-1 adjacency, with proper Level-2 reachability across areas.
- 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.
- Copy a route map verbatim into IOS XR policy syntax and assume it preserves implicit deny and pass behavior.
Explanation
Correct Answer
C:This targeted action addresses the observed service-provider control or forwarding gap without discarding necessary controls. Applied case: A provider's import filter matches all routes because a broad prefix set is evaluated before the more specific deny policy for leaked routes.
Incorrect Answers
A:Verify OSPFv3 interface activation, matching area and instance settings and IPv6 address-family route advertisement before expecting end-to-end forwarding. Route filtering is an ordered policy decision with platform-specific syntax and implicit outcomes; bad matching or direction can leak or drop routes.
B:Assign unique IS-IS system IDs and consistent area identifiers for Level-1 adjacency, with proper Level-2 reachability across areas. Route filtering is an ordered policy decision with platform-specific syntax and implicit outcomes; bad matching or direction can leak or drop routes.
D:Route filtering is an ordered policy decision with platform-specific syntax and implicit outcomes; bad matching or direction can leak or drop routes. Use this instead: 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.
Question 252
A Cisco service provider design review finds: A provider's import filter matches all routes because a broad prefix set is evaluated before the more specific deny policy for leaked routes. The team proposes: 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. 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.
- Route filtering is an ordered policy decision with platform-specific syntax and implicit outcomes; bad matching or direction can leak or drop routes.
- Single topology shares reachability assumptions across enabled families, while multi-topology can maintain distinct IPv4 and IPv6 topology information.
- 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
B:Relevant validation before approval: Evaluate a test table with allowed, denied and boundary prefixes against actual show-policy and BGP advertised-routes evidence. Applied case: A provider's import filter matches all routes because a broad prefix set is evaluated before the more specific deny policy for leaked routes.
Incorrect Answers
A:This option addresses a different service provider engineering topic (NAT64 CGNAT MAP-T DS-Lite and transition selection) rather than the documented IOS XR route policy language and Cisco route maps decision.
C:Single topology shares reachability assumptions across enabled families, while multi-topology can maintain distinct IPv4 and IPv6 topology information. Route filtering is an ordered policy decision with platform-specific syntax and implicit outcomes; bad matching or direction can leak or drop routes.
D:IS-IS adjacencies use link-local protocol hellos and compatible level, circuit and network settings; IP reachability alone does not create a neighbor. Route filtering is an ordered policy decision with platform-specific syntax and implicit outcomes; bad matching or direction can leak or drop routes.
Question 253
The service provider operations team has not yet approved a change. Current evidence indicates: A provider's import filter matches all routes because a broad prefix set is evaluated before the more specific deny policy for leaked routes. Which evidence best tests the technical diagnosis before approving a disruptive change? Select ONE best answer.
- Inspect BGP neighbor transport state, local and remote AS, update source, TCP reachability and IPv4 or IPv6 address-family activation.
- Review link metric TLVs, enabled metric style, SPF database and before-after path selection for two candidate routes.
- Evaluate a test table with allowed, denied and boundary prefixes against actual show-policy and BGP advertised-routes evidence.
- Compare BFD session state, negotiated intervals, packet drops and routing convergence after controlled loss and benign congestion tests.
Explanation
Correct Answer
C:Route filtering is an ordered policy decision with platform-specific syntax and implicit outcomes; bad matching or direction can leak or drop routes. Applied case: A provider's import filter matches all routes because a broad prefix set is evaluated before the more specific deny policy for leaked routes.
Incorrect Answers
A:Inspect BGP neighbor transport state, local and remote AS, update source, TCP reachability and IPv4 or IPv6 address-family activation. Route filtering is an ordered policy decision with platform-specific syntax and implicit outcomes; bad matching or direction can leak or drop routes.
B:Review link metric TLVs, enabled metric style, SPF database and before-after path selection for two candidate routes. Route filtering is an ordered policy decision with platform-specific syntax and implicit outcomes; bad matching or direction can leak or drop routes.
D:Compare BFD session state, negotiated intervals, packet drops and routing convergence after controlled loss and benign congestion tests. Route filtering is an ordered policy decision with platform-specific syntax and implicit outcomes; bad matching or direction can leak or drop routes.
Question 254
A candidate correction has been tested and the platform team requires a post-change acceptance check. Original problem: A provider's import filter matches all routes because a broad prefix set is evaluated before the more specific deny policy for leaked routes. 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.
- Accepted members forward correctly, aggregate capacity reflects active links and service survives an individual member failure.
- Stable OSPFv3 adjacencies advertise the intended IPv6 prefixes with reachable next hops.
- Authorized prefixes are imported or exported and unintended customer or infrastructure prefixes are rejected without adjacency disruption.
- Selected paths follow intended costs and the backup route takes over safely after a neighbor or link failure.
Explanation
Correct Answer
C:Route filtering is an ordered policy decision with platform-specific syntax and implicit outcomes; bad matching or direction can leak or drop routes. The result must be validated using the documented device, service or access context.
Incorrect Answers
A:Accepted members forward correctly, aggregate capacity reflects active links and service survives an individual member failure. Route filtering is an ordered policy decision with platform-specific syntax and implicit outcomes; bad matching or direction can leak or drop routes.
B:Stable OSPFv3 adjacencies advertise the intended IPv6 prefixes with reachable next hops. Route filtering is an ordered policy decision with platform-specific syntax and implicit outcomes; bad matching or direction can leak or drop routes.
D:Selected paths follow intended costs and the backup route takes over safely after a neighbor or link failure. Route filtering is an ordered policy decision with platform-specific syntax and implicit outcomes; bad matching or direction can leak or drop routes.
Question 255
An implementation sign-off request identifies the following problem: A provider's import filter matches all routes because a broad prefix set is evaluated before the more specific deny policy for leaked routes. Which paired technical change and validation should close the implementation review? Select ONE best answer.
- Change: Assign unique IS-IS system IDs and consistent area identifiers for Level-1 adjacency, with proper Level-2 reachability across areas. Verify: Examine NET values, level adjacency state, LSP originator IDs and intended area boundaries on a two-area diagram.
- Change: Choose documented BGP ingress-traffic engineering signals and verify how relevant peers actually compare received alternatives. Verify: Examine advertised route attributes per peer, remote looking-glass paths and measured ingress flows before and after the change.
- 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: 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. Verify: Evaluate a test table with allowed, denied and boundary prefixes against actual show-policy and BGP advertised-routes evidence.
Explanation
Correct Answer
D:Route filtering is an ordered policy decision with platform-specific syntax and implicit outcomes; bad matching or direction can leak or drop routes. The change is successful only when: Authorized prefixes are imported or exported and unintended customer or infrastructure prefixes are rejected without adjacency disruption.
Incorrect Answers
A:Change: Assign unique IS-IS system IDs and consistent area identifiers for Level-1 adjacency, with proper Level-2 reachability across areas. Route filtering is an ordered policy decision with platform-specific syntax and implicit outcomes; bad matching or direction can leak or drop routes.
B:Change: Choose documented BGP ingress-traffic engineering signals and verify how relevant peers actually compare received alternatives. Route filtering is an ordered policy decision with platform-specific syntax and implicit outcomes; bad matching or direction can leak or drop routes.
C:This option addresses a different service provider engineering topic (BGP route-policy communities and provider preference) rather than the documented IOS XR route policy language and Cisco route maps decision.
Question 256
A service provider network engineer is reviewing this backbone or customer-service scenario: A migration redistributes every customer BGP route into the IGP and overwhelms core LSDB memory while leaking unrelated service prefixes. 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.
- Restrict redistribution using explicit route policy and tags, and maintain a scalable separation of service prefixes from core IGP reachability.
- Select single- or multi-topology IS-IS according to dual-stack forwarding requirements and verify both address-family reachability and advertised topology data.
- Redistribute the entire global BGP table into OSPF or IS-IS and rely on implicit loop protection.
- 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: A migration redistributes every customer BGP route into the IGP and overwhelms core LSDB memory while leaking unrelated service prefixes.
Incorrect Answers
B:Select single- or multi-topology IS-IS according to dual-stack forwarding requirements and verify both address-family reachability and advertised topology data. Redistribution changes protocol scope and metrics; uncontrolled mutual redistribution can create loops and excessive IGP state.
C:Redistribution changes protocol scope and metrics; uncontrolled mutual redistribution can create loops and excessive IGP state. For this best change assessment, the shortcut changes or bypasses the necessary routing, service or operational boundary rather than correcting it.
D:Enable compatible path diversity or BGP PIC mechanisms where supported and verify backup data-plane programming before a failure. Redistribution changes protocol scope and metrics; uncontrolled mutual redistribution can create loops and excessive IGP state.
Question 257
A Cisco service provider design review finds: A migration redistributes every customer BGP route into the IGP and overwhelms core LSDB memory while leaking unrelated service prefixes. 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.
- Route filtering is an ordered policy decision with platform-specific syntax and implicit outcomes; bad matching or direction can leak or drop routes.
- OSPF area types control which LSA classes are accepted while ABRs can summarize routes; a summary may hide unavailable more-specifics if chosen carelessly.
- BGP TCP sessions depend on correct peer identity and routed transport; external versus internal peer behavior changes next-hop and forwarding assumptions.
- Redistribution changes protocol scope and metrics; uncontrolled mutual redistribution can create loops and excessive IGP state.
Explanation
Correct Answer
D: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: A migration redistributes every customer BGP route into the IGP and overwhelms core LSDB memory while leaking unrelated service prefixes.
Incorrect Answers
A:Route filtering is an ordered policy decision with platform-specific syntax and implicit outcomes; bad matching or direction can leak or drop routes. Redistribution changes protocol scope and metrics; uncontrolled mutual redistribution can create loops and excessive IGP state.
B:OSPF area types control which LSA classes are accepted while ABRs can summarize routes; a summary may hide unavailable more-specifics if chosen carelessly. Redistribution changes protocol scope and metrics; uncontrolled mutual redistribution can create loops and excessive IGP state.
C:BGP TCP sessions depend on correct peer identity and routed transport; external versus internal peer behavior changes next-hop and forwarding assumptions. Redistribution changes protocol scope and metrics; uncontrolled mutual redistribution can create loops and excessive IGP state.
Question 258
The service provider operations team has not yet approved a change. Current evidence indicates: A migration redistributes every customer BGP route into the IGP and overwhelms core LSDB memory while leaking unrelated service prefixes. Which evidence best tests the technical diagnosis before approving a disruptive change? Select ONE best answer.
- Inspect BGP neighbor transport state, local and remote AS, update source, TCP reachability and IPv4 or IPv6 address-family activation.
- 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.
- 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. Applied case: A migration redistributes every customer BGP route into the IGP and overwhelms core LSDB memory while leaking unrelated service prefixes.
Incorrect Answers
A:Inspect BGP neighbor transport state, local and remote AS, update source, TCP reachability and IPv4 or IPv6 address-family activation. Redistribution changes protocol scope and metrics; uncontrolled mutual redistribution can create loops and excessive IGP state.
B:Inspect IPv6 link-local neighbors, interface instance and area data, OSPFv3 LSDB and installed IPv6 routes. Redistribution changes protocol scope and metrics; uncontrolled mutual redistribution can create loops and excessive IGP state.
C:Compare per-protocol neighbor state, error messages, encapsulation, path reachability, authentication and interface counters. Redistribution changes protocol scope and metrics; uncontrolled mutual redistribution can create loops and excessive IGP state.
Question 259
A candidate correction has been tested and the platform team requires a post-change acceptance check. Original problem: A migration redistributes every customer BGP route into the IGP and overwhelms core LSDB memory while leaking unrelated service prefixes. 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.
- Accepted members forward correctly, aggregate capacity reflects active links and service survives an individual member failure.
- Intended EBGP adjacencies establish securely and exchange only approved prefixes in the selected address family.
- Only planned prefixes cross the protocol boundary once and core convergence remains stable under service-route churn.
- Valid alternate paths are visible and traffic shifts within expected service objectives when the primary next hop fails.
Explanation
Correct Answer
C:Redistribution changes protocol scope and metrics; uncontrolled mutual redistribution can create loops and excessive IGP state. The result must be validated using the documented device, service or access context.
Incorrect Answers
A:Accepted members forward correctly, aggregate capacity reflects active links and service survives an individual member failure. Redistribution changes protocol scope and metrics; uncontrolled mutual redistribution can create loops and excessive IGP state.
B:Intended EBGP adjacencies establish securely and exchange only approved prefixes in the selected address family. Redistribution changes protocol scope and metrics; uncontrolled mutual redistribution can create loops and excessive IGP state.
D:Valid alternate paths are visible and traffic shifts within expected service objectives when the primary next hop fails. Redistribution changes protocol scope and metrics; uncontrolled mutual redistribution can create loops and excessive IGP state.
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.
