10 free Cisco 300-420 ENSLD practice questions with the correct answer and a full explanation for each, taken from the CertStash pack of 417 questions. Work through them, then open each answer to check your reasoning.
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Question 1
Which two BGP features will result in successful route exchanges between eBGP neighbors sharing the same AS number? (Choose two.)
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Correct answer: D, E
D. as-override E. allow-as-in When eBGP neighbors share the same AS number (typically in confederation or complex topologies), route exchanges are blocked by default. The as-override command allows routes from the same AS to be accepted by replacing the AS number in the AS path, enabling the exchange. The allow-as-in command permits a router to accept routes that contain its own AS number in the AS path, which is necessary when neighbors share the same AS. Both features directly enable this non-standard configuration.
Why the other options are wrong
- A. advertise-best-external advertises only the best external route but does not address the same-AS rejection mechanism.
- B. bestpath as-path ignore disables AS path comparison for best path selection but does not allow same-AS routes through the initial acceptance filter.
- C. client-to-client reflection is an iBGP feature for route reflector clients and is unrelated to eBGP same-AS scenarios.
Question 2
A customer with an IPv4 only network topology wants to enable IPv6 connectivity while preserving the IPv4 topology services. The customer plans to migrate IPv4 services to the IPv6 topology, then decommission the IPv4 topology.
Which topology supports these requirements?
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Correct answer: A. dual stack
Dual stack networking runs both IPv4 and IPv6 simultaneously on the same network infrastructure, allowing the customer to preserve existing IPv4 services while gradually migrating them to IPv6. Once IPv4 services are moved and validated on IPv6, the IPv4 topology can be decommissioned. This satisfies the requirement of coexistence during transition followed by eventual IPv4 removal.
Why the other options are wrong
- B. 6VPE is a technique for carrying IPv6 over MPLS but does not provide the dua-rotocol coexistence needed for gradual service migration.
- C. 6to4 is a tunneling mechanism that encapsulates IPv6 in IPv4 for transit across IPv4 networks; it is not suited for managing parallel topology operation and migration.
- D. NAT64 translates between IPv6 and IPv4 protocols but does not preserve independent parallel topologies for gradual service migration.
Question 3
A company is running BGP on a single router, which has two connections to the same ISP.
Which BGP feature ensures traffic is load balanced across the two links to the ISP?
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Correct answer: B. Multipath Load Sharing
Multipath Load Sharing (also called Equal-Cost Multipath or ECMP) allows BGP to install multiple equal-cost routes in the routing table and distribute traffic across them. When a router has two equal-cost paths to the same destination via the same ISP, multipath load sharing enables traffic to be balanced across both links.
Why the other options are wrong
- A. Multihop extends the TTL for eBGP sessions beyond the default single hop but does not address load balancing.
- C. Next-Hop Address Tracking monitors reachability of BGP next hops but does not implement load balancing across equal paths.
- D. AS-Path Prepending artificially increases AS path length to make a route less preferred, used to influence inbound traffic, not to load balance outbound traffic across equal paths.
Question 4
Company A recently acquired another company. Users of the newly acquired company must be able to access a server that exists on Company A's network, both companies use overlapping IP address ranges.
Which action conserves IP address space and provides access to the server?
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Correct answer: A. Use a single IP address to create overload NAT
Overload NAT (also called PAT, Port Address Translation) translates multiple private IP addresses to a single public IP address by using different port numbers, conserving IP address space. This allows users from the acquired company with overlapping private IP ranges to access the server on Company A's network through one mapped IP address with port-based differentiation.
Why the other options are wrong
- B. Static NAT creates one-to-one translations, which would require separate public addresses for each user, defeating the space conservation requirement.
- C. Building one-to-one NAT for every user would require multiple IP addresses, not conserving space.
- D. Re-IPing the acquired company's network is operationally disruptive and does not conserve space on either side; it simply moves the problem.
Question 5
Which design consideration should be observed when EIGRP is configured on Data Center switches?
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Correct answer: B. Prevent unnecessary EIGRP neighborships from forming across switch virtual interfaces.
In data center environments with many switch virtual interfaces (SVIs), preventing unnecessary EIGRP neighborships reduces protocol overhead, CPU consumption, and stability issues. EIGRP should be selectively enabled only on interfaces that require it, avoiding adjacencies across SVIs that are purely for management or inter-VLAN routing without a need for dynamic neighbor discovery.
Why the other options are wrong
- A. While summarization is beneficial, it is not a primary design consideration specific to data center switches; manual summarization on all Layer 3 interfaces is overly prescriptive.
- C. Lowering hello and hold timers to minimum values increases CPU load and convergence noise; data centers typically benefit from stable, tuned timers rather than aggressive minimums.
- D. Running multiple EIGRP autonomous systems segments routing but adds complexity and is not a standard data center design consideration; it contradicts simplicity principles.
Question 6
Which design consideration must be made when using IPv6 overlay tunnels?
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Correct answer: B. Overlay tunnels should only be considered as a transition technique toward a permanent solution.
IPv6 overlay tunnels are temporary mechanisms that allow isolated IPv6 networks to communicate across IPv4 infrastructure during a transition period. They are not intended as a permanent solution; the network should eventually be redesigned to use native IPv6 end-to-end. This principle ensures that tunnel overhead and complexity are minimized by planning for their eventual replacement with a proper dual-stack or native IPv6 architecture.
Why the other options are wrong
- A. Overlay tunnels that connect isolated IPv6 networks are explicitly a transitional, not final, architecture.
- C. Overlay tunnels require both IPv4 and IPv6 protocol stacks and must span across IPv4 infrastructure, not just connect border devices.
- D. IPv6 overlay tunneling encapsulates IPv6 packets in IPv4 packets for delivery across an IPv4 infrastructure, not the reverse.
Question 7
When a network is designed using IS-IS, which two circuit types are supported? (Choose two.)
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Correct answer: B, E
B. multiaccess E. point-to-point IS-IS supports point-to-point and nonbroadcast circuit types. Point-to-point circuits connect two routers directly without the need for a designated intermediate system. Nonbroadcast circuits are used on networks where broadcast is not available, requiring manual configuration of neighbors. These are the two primary circuit types defined in the IS-IS standard.
Why the other options are wrong
- A. Nonbroadcast multiaccess (NBMA) is an OSPF term, not an IS-IS circuit type.
- C. Point-to-multipoint is an OSPF circuit type, not supported as a standard IS-IS circuit type.
- D. Nonbroadcast alone is covered under option B; it is not listed separately as a distinct IS-IS circuit type designation.
Question 8
A network solution is being designed for a company that connects to multiple Internet service providers.
Which Cisco proprietary BGP path attribute will influence outbound traffic flow?
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Correct answer: C. Weight
Weight is a Cisco proprietary BGP attribute that influences outbound traffic flow on the local router. It is evaluated first in the BGP best path selection algorithm and higher weight values are preferred. Weight affects which route is selected and advertised out, directly controlling the direction of outbound traffic from the local AS.
Why the other options are wrong
- A. Local Preference is a standard attribute, not proprietary to Cisco, and influences inbound traffic selection from other routers in the same AS.
- B. MED is a standard attribute used to influence inbound traffic from specific eBGP neighbors, not outbound traffic.
- D. AS Path is a standard attribute; while it affects route selection, it is not proprietary and is evaluated after weight.
- E. Community is a standard attribute used for tagging and filtering routes, not specifically for influencing outbound traffic flow.
Question 9
Refer to the exhibit. EIGRP has been configured on all links. The spoke nodes have been configured as EIGRP stubs, and the WAN links to R3 have higher bandwidth and lower delay than the WAN links to R4.
When a link failure occurs at the R1-R2 link, what happens to traffic on R1 that is destined for a subnet attached to R2?
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Correct answer: A. R1 has no route to R2 and drops the traffic
In this hub-and-spoke topology, R3 and R4 are configured as EIGRP stub routers. EIGRP stub routers do not advertise routes learned from other spokes and do not accept route queries from the hub. When the direct R1-R2 link fails, R1 loses its direct connection and would need an alternative path. However, R3 and R4 (the spokes) cannot provide transit routes to reach R2 through them because they are stub nodes. Stub routers only advertise their directly connected networks and connected routes, not routes learned from other spokes. Therefore, R1 has no valid route to R2 and must drop the traffic destined for R2's subnets.
Why the other options are wrong
- B. Load balancing would only occur if R3 and R4 could provide valid routes to R2, which they cannot as EIGRP stubs that do not forward inter-spoke traffic.
- C. While R1 would forward traffic to R3 as an attempt to reach R2, R3 drops it because stubs do not provide transit routing; this outcome is partially correct but incomplete compared to the direct answer that R1 simply has no route.
- D. R1 will not forward traffic to R3 as a viable path because R3, as a stub, cannot provide a route to R2 and will not accept or forward such queries.
Question 10
A company is using OSPF between its HQ location and a branch office. HQ is assigned area 0 and the branch office is assigned area 1. The company purchases a second branch office, but due to circuit delays to HQ, it decides to connect the new branch office to the existing branch office as a temporary measure. The new branch office is assigned to area 2. Which OSPF configuration enables all three locations to exchange routes?
Show answer and explanation
Correct answer: B. A virtual link must be configured between the new branch office and HQ
In OSPF, all areas must have a path to the backbone area (Area 0). When Area 2 is connected only to Area 1 (non-backbone), it cannot directly reach Area 0. A virtual link must be configured between Area 1 and Area 2, treating the path through Area 1 as a virtual backbone connection. This allows Area 2 to logically connect to the backbone and exchange routes with all locations. Virtual links are the standard OSPF mechanism for this topology requirement.
Why the other options are wrong
- A. Configuring Area 1 as a stub area prevents it from receiving external routes but does not enable Area 2 to reach Area 0, and a stub area still requires backbone connectivity.
- C. Sham links are used in MPLS-TE environments to affect SPF calculations and are not applicable for standard OSPF area connectivity issues.
- D. Configuring Area 2 as a stub area does not solve the fundamental problem that Area 2 lacks connectivity to the backbone area through a valid OSPF path.
That was 10 of 417.
The full Cisco 300-420 ENSLD pack has all 417 questions, each with the answer, the explanation and why the other options are wrong, plus a questions-only copy for timed runs. US$39, paid once, with free monthly updates and a pass-or-your-money-back guarantee.