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300-420 exam dumps: 323 free Cisco ENSLD practice questions

Free 300-420 practice questions for the Designing Cisco Enterprise Networks exam, with the correct answer and a full explanation for every option. Read the first 10 below, browse all 323 by number, or take a timed practice exam.

Question bank last updated February 2025

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Free 300-420 practice questions

Questions 1 to 10 of 323

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300-420 Question 1

Single answer

An enterprise network is migrating to a dual-homed topology to improve redundancy and high availability. The network design includes multiple branch offices connected to two different ISPs. The branches are configured to use BGP for external routing, and the requirement is to ensure that traffic destined to the internet is always routed through the primary ISP unless it becomes unavailable. Additionally, the network should maintain proper failover to the secondary ISP during outages. Which solution meets this requirement?

A
Configure local preference in BGP advertisements from the primary ISP to influence outbound traffic.
B
Use AS path prepending for routes advertised to the secondary ISP to make them less preferred.
C
Implement BGP community attributes to tag routes and influence inbound traffic from the internet.
D
Configure MED (Multi-Exit Discriminator) to prioritize the primary ISP for inbound traffic.

Show answer and explanation

Correct answer: B

Explanation

The requirement is to prioritize the primary ISP for internet traffic and use the secondary ISP only during outages. AS path prepending is a commonly used technique in BGP to ensure that routes advertised to the secondary ISP appear less preferred to external networks. This design ensures proper failover to the secondary ISP while maintaining primary ISP preference under normal conditions.

A. Incorrect.
Local preference influences the outbound routing decisions within an AS but does not directly control failover or influence routes advertised to ISPs.
B. Correct.
AS path prepending is used to manipulate route preferences by making routes appear less attractive to external peers, which ensures the secondary ISP is only used if the primary ISP fails.
C. Incorrect.
BGP community attributes are used to mark routes with specific tags for policy application but are not directly used for ensuring traffic prioritization for failover scenarios.
D. Incorrect.
MED influences inbound traffic preferences when multiple exit points exist within a neighboring AS, but it is not the best solution for the given scenario.

300-420 Question 2

Single answer

A large enterprise network is implementing a hierarchical addressing scheme to optimize routing performance and reduce the size of routing tables. The goal is to ensure that branch offices can be summarized at the aggregation layer while maintaining connectivity to the core. Which design principle should be followed to achieve this goal?

A
Use Variable Length Subnet Masking (VLSM) to allocate IP addresses based on each branch office's requirements.
B
Assign overlapping IP address ranges to branch offices to simplify summarization.
C
Design the IP addressing scheme to align with the physical topology and use contiguous address blocks for summarization.
D
Deploy a flat IP addressing scheme to ensure consistency across all devices in the network.

Show answer and explanation

Correct answer: C

Explanation

To achieve efficient route summarization at the aggregation layer, the IP addressing scheme must align with the physical network topology and use contiguous address blocks. This approach allows branch office routes to be summarized effectively, reducing the size of routing tables and enhancing network performance.

A. Incorrect.
This is a good practice for efficient IP address allocation, but it does not directly address summarization or routing table optimization. VLSM alone cannot ensure summarization at the aggregation layer.
B. Incorrect.
Assigning overlapping IP address ranges would cause routing conflicts and disrupt network connectivity. This violates fundamental IP addressing principles.
C. Correct.
Designing the IP addressing scheme to align with the physical topology and using contiguous address blocks enables effective route summarization. This approach reduces routing table size and simplifies network management.
D. Incorrect.
A flat IP addressing scheme does not allow for summarization, which would result in larger routing tables and inefficient routing in large-scale networks.

300-420 Question 3

Single answer

An enterprise network consists of multiple branch offices connected to a central data center through an MPLS service provider. The company plans to implement a failover mechanism between the MPLS network and a new VPN over the internet to ensure high availability. Which routing solution should you implement to prioritize MPLS connectivity while automatically switching to VPN in case of a failure?

A
Configure static routes with a lower administrative distance for MPLS and higher administrative distance for VPN.
B
Implement BGP with route reflectors to dynamically advertise MPLS and VPN routes.
C
Use OSPF with MPLS routes assigned to Area 0 and VPN routes assigned to a stub area.
D
Configure EIGRP with MPLS routes having a higher feasible distance compared to VPN routes.

Show answer and explanation

Correct answer: A

Explanation

Static routes with different administrative distances provide a simple and effective way to implement failover between MPLS and VPN. The primary route (MPLS) is chosen based on its lower administrative distance, and the backup route (VPN) is used only if the primary route fails. This ensures high availability without requiring complex configurations.

A. Correct.
This is the correct option. By using static routes with a lower administrative distance for MPLS and higher administrative distance for VPN, MPLS will be preferred by default while VPN will act as a failover path if MPLS fails.
B. Incorrect.
While BGP allows dynamic route advertisement, it does not inherently prioritize one path over another without additional configuration like local preference or AS-path manipulation, making it less straightforward for this scenario.
C. Incorrect.
OSPF's area designations do not prioritize routes between different areas in this manner. It would not be a suitable solution for implementing failover between MPLS and VPN.
D. Incorrect.
In EIGRP, the feasible distance does not control primary and backup route selection. Administrative distance would need to be adjusted for proper prioritization, which is not mentioned here.

300-420 Question 4

Select 3

An enterprise network is experiencing suboptimal routing between its branch offices and data center due to asymmetric routing. The network uses OSPF as the IGP with multiple areas configured. A design engineer proposes implementing a summarization strategy to fix the issue. What considerations should be taken into account when designing OSPF summarization in this scenario?

A
OSPF summarization should only be implemented at Area Border Routers (ABRs) or Autonomous System Boundary Routers (ASBRs).
B
Summarization in OSPF can lead to loss of visibility into specific subnets for troubleshooting.
C
OSPF supports automatic summarization, so manual summarization is not required in this scenario.
D
Summarization will reduce the size of the OSPF database and improve convergence time.
E
OSPF summarization is not recommended when all areas in the network are configured as OSPF Area 0.

Show answer and explanation

Correct answers: A, B, D

Explanation

OSPF summarization is a key design consideration in multi-area OSPF networks to optimize routing and improve scalability. By summarizing routes at ABRs and ASBRs, network designers can reduce the size of the OSPF database, improve convergence time, and enhance network stability. However, this approach comes with the trade-off of losing detailed visibility into specific subnets, which can impact troubleshooting efforts. Summarization must be manually configured and is not applicable in single-area OSPF designs, such as when all areas are configured as Area 0.

A. Correct.
Correct: OSPF summarization is only performed at ABRs and ASBRs, as these devices separate OSPF areas or external domains, making it the correct location for summarization.
B. Correct.
Correct: While summarization reduces routing table size, it hides detailed subnet information, which can complicate troubleshooting.
C. Incorrect.
Incorrect: OSPF does not support automatic summarization; summarization must be manually configured by the network administrator.
D. Correct.
Correct: Summarization reduces the size of the OSPF database by aggregating routes and improves convergence time by reducing the number of LSAs in the network.
E. Incorrect.
Incorrect: Summarization is specifically useful in multi-area OSPF designs. It is not applicable if all areas are configured as Area 0, but this does not mean summarization is not recommended in general.

300-420 Question 5

Select 3

You are tasked with designing an enterprise-wide addressing plan for both IPv4 and IPv6. The organization has multiple regional offices and requires a hierarchical addressing scheme to simplify routing and management. Each region must have its own subnet with enough address space to accommodate future growth. Which of the following principles should you follow to create a structured addressing plan?

A
Use variable-length subnet masking (VLSM) to allocate address space based on the size of each region's network.
B
Design the IPv4 subnet mask to allocate all available addresses in a single subnet to maximize address utilization.
C
Use hierarchical addressing to create regional subnets for both IPv4 and IPv6 to simplify summarization.
D
Reserve a large portion of IPv6 space for future expansion by allocating a /64 prefix to each regional network.
E
Avoid using private IPv4 addresses to ensure global uniqueness of the addressing plan.

Show answer and explanation

Correct answers: A, C, D

Explanation

To create a structured addressing plan for both IPv4 and IPv6, it is crucial to use VLSM to allocate address space efficiently, implement hierarchical addressing to simplify routing, and follow IPv6 best practices such as using /64 prefixes for regional subnets to support future growth. These principles ensure scalability, efficient address utilization, and simplified network operations.

A. Correct.
Using VLSM ensures efficient use of address space by allocating subnets with the exact number of required addresses, which supports scalability while preventing waste.
B. Incorrect.
Allocating all available IPv4 addresses into a single subnet does not align with best practices for hierarchical addressing, as it complicates routing and lacks scalability.
C. Correct.
Hierarchical addressing is critical for creating a structured addressing plan, as it simplifies route summarization and reduces the size of routing tables.
D. Correct.
Allocating a /64 prefix to each regional network aligns with IPv6 best practices and supports future growth, as a /64 is the standard size for most subnets.
E. Incorrect.
Avoiding private IPv4 addresses is not a best practice in enterprise networks, as private address ranges (defined by RFC 1918) are widely used and appropriate for internal addressing.

300-420 Question 6

Select 2

An enterprise network is expanding its services globally and requires an efficient IPv4 and IPv6 addressing plan. The plan must ensure scalability, minimize routing table entries, and support future growth. Which two design principles should you follow when creating the addressing plan?

A
Use summarization to aggregate contiguous address blocks.
B
Assign addresses on a first-come, first-served basis to maximize address usage.
C
Implement a hierarchical addressing scheme based on geographic and organizational boundaries.
D
Use overlapping address ranges to optimize address space utilization.
E
Allocate IPv6 addresses with a /128 prefix to each device for simplicity.

Show answer and explanation

Correct answers: A, C

Explanation

Creating a structured addressing plan for IPv4 and IPv6 requires scalability, efficiency, and adherence to best practices. Summarization reduces routing complexity, while a hierarchical addressing scheme ensures logical and scalable allocation. These principles are critical for enterprise networks to support growth and operational simplicity.

A. Correct.
Summarization helps reduce the size of routing tables by aggregating contiguous address blocks, thereby improving scalability and simplifying routing.
B. Incorrect.
Assigning addresses on a first-come, first-served basis can lead to fragmentation and inefficiency, making it unsuitable for structured addressing plans.
C. Correct.
A hierarchical addressing scheme allows for logical segmentation of the address space, which improves scalability, manageability, and supports future growth.
D. Incorrect.
Overlapping address ranges cause conflicts and routing issues, which violate the principles of a structured addressing plan.
E. Incorrect.
Allocating /128 prefixes to devices is inefficient and does not align with IPv6 best practices, which recommend using /64 prefixes for most subnets.

300-420 Question 7

Single answer

Your organization is planning to implement a dual-stack strategy to support both IPv4 and IPv6. The network consists of five departments, each requiring 500 devices to be accommodated in the addressing plan. For IPv4, you have been allocated the 192.168.0.0/22 range, and for IPv6, you have been allocated a /48 prefix (2001:db8:abcd::/48). What is the most appropriate addressing plan to meet the requirements while minimizing wasted addresses?

A
Use a /25 subnet for each department in IPv4 and a /64 subnet for each department in IPv6.
B
Use a /24 subnet for each department in IPv4 and a /63 subnet for each department in IPv6.
C
Use a /23 subnet for each department in IPv4 and a /64 subnet for each department in IPv6.
D
Use a /27 subnet for each department in IPv4 and a /56 subnet for each department in IPv6.

Show answer and explanation

Correct answer: A

Explanation

The correct addressing plan must balance efficiency and scalability. Using a /25 subnet for IPv4 provides the necessary 500 device support with minimal wasted addresses, as each department will use 128 IPs. For IPv6, a /64 subnet is the standard and recommended size for subnets, ensuring compatibility with modern IPv6 deployments. This approach meets the organization's requirements while adhering to best practices.

A. Correct.
This is correct. A /25 subnet for IPv4 provides 128 addresses, which is sufficient for the 500 devices required per department. For IPv6, a /64 subnet is the standard recommendation for host subnets, ensuring scalability and compatibility.
B. Incorrect.
This is incorrect. A /24 subnet for IPv4 provides 256 addresses, which is insufficient for 500 devices. Additionally, a /63 subnet for IPv6 is not a standard practice and is generally reserved for specific use cases.
C. Incorrect.
This is incorrect. A /23 subnet for IPv4 provides 512 addresses, which meets the requirement but wastes a significant number of unused IPs given the 500-device requirement. A /64 for IPv6 is correct, but the IPv4 inefficiency makes this option less optimal.
D. Incorrect.
This is incorrect. A /27 subnet for IPv4 provides only 32 addresses, which is far below the required 500 addresses. For IPv6, a /56 is unnecessarily large for a single department in this scenario.

300-420 Question 8

Select 2

An enterprise network is planning to deploy a structured IPv4 and IPv6 addressing plan. The network consists of four departments: Sales, HR, IT, and Finance. Each department requires its own IPv4 subnet and IPv6 subnet, and the addressing plan must allow for future growth in each department. Which of the following practices should be followed when designing this addressing plan?

A
Use Variable Length Subnet Masking (VLSM) for IPv4 to allocate subnet sizes based on department needs.
B
Allocate a /48 IPv6 prefix to each department to ensure scalability.
C
Use a hierarchical addressing scheme to group subnets by department and geographical location.
D
Reuse IPv4 private address space (e.g., 10.0.0.0/8) across different departments for simplicity.
E
Avoid reserving additional IP space for future growth to maximize current address utilization.

Show answer and explanation

Correct answers: A, C

Explanation

When designing a structured addressing plan, it is important to implement practices that ensure scalability, organization, and efficient address utilization. Using VLSM for IPv4 helps allocate address space based on specific needs without wastage. A hierarchical addressing scheme enables better organization and simplifies management and routing. Allocating excessively large prefixes (e.g., /48 for each department in IPv6) or failing to reserve space for growth can result in inefficiencies or future operational challenges.

A. Correct.
Using VLSM allows the network to allocate IPv4 address space efficiently by assigning subnets based on the specific size requirements of each department.
B. Incorrect.
Allocating a /48 IPv6 prefix to each department is not efficient for most enterprise networks. A /64 per subnet is the standard practice, and departments generally require fewer than /48 blocks.
C. Correct.
A hierarchical addressing scheme ensures better organization and easier route summarization as the network grows, making it a best practice for scalability and management.
D. Incorrect.
Reusing IPv4 private address space across departments can lead to overlapping address issues and complicate routing and troubleshooting.
E. Incorrect.
Avoiding reservation for future growth is a poor practice as it can lead to address exhaustion and require major reconfiguration later.

300-420 Question 9

Select 3

You are designing a large-scale enterprise network that utilizes IS-IS as the IGP. The network will consist of multiple areas and require scalability while ensuring stability and security. Which of the following design considerations should you implement to achieve these goals?

A
Use a hierarchical area structure with Level 1 and Level 2 separation.
B
Enable wide metrics to support high-bandwidth links and scalability.
C
Disable authentication to simplify configuration and reduce processing overhead.
D
Avoid configuring overload-bit in scenarios where the router's resources are limited.
E
Implement IS-IS authentication to secure routing updates.

Show answer and explanation

Correct answers: A, B, E

Explanation

Designing a stable, secure, and scalable IS-IS routing architecture requires a combination of hierarchical design, modern feature utilization (such as wide metrics), and robust security mechanisms like authentication. Hierarchical area separation reduces routing overhead, wide metrics support scalability, and authentication ensures routing updates are secure. Avoiding best practices like overload-bit configuration in resource-constrained scenarios or disabling authentication can lead to instability and security vulnerabilities.

A. Correct.
Using a hierarchical area structure with Level 1 and Level 2 separation improves scalability and reduces the size of the LSDB within each area, enhancing stability.
B. Correct.
Enabling wide metrics allows IS-IS to support higher-bandwidth links and provides better scalability for modern networks.
C. Incorrect.
Disabling authentication is not recommended as it exposes the network to potential attacks, compromising security.
D. Incorrect.
Configuring the overload-bit is a best practice in scenarios where router resources are constrained. Avoiding it can lead to instability in the network.
E. Correct.
Implementing IS-IS authentication secures routing updates, preventing unauthorized or malicious changes to the routing table.

300-420 Question 10

Select 3

A large enterprise network is implementing Intermediate System-to-Intermediate System (IS-IS) for its campus and data center environments. The network team wants to design a stable, secure, and scalable routing solution. Which two design considerations should be implemented to achieve this goal?

A
Enable IS-IS authentication to protect routing updates from unauthorized sources.
B
Use a single large IS-IS area to simplify route propagation and reduce complexity.
C
Configure overload bit settings on specific routers to influence route selection during maintenance or startup.
D
Disable IS-IS metric-based traffic engineering to avoid complexity in routing decisions.
E
Implement route summarization between IS-IS areas to optimize the size of routing tables.

Show answer and explanation

Correct answers: A, C, E

Explanation

Designing a stable, secure, and scalable IS-IS routing solution involves key considerations such as ensuring security through authentication, optimizing scalability with techniques like route summarization, and enhancing stability by using features like the overload bit for route control during specific conditions. These practices collectively ensure the network operates efficiently and securely while accommodating growth.

A. Correct.
Enabling IS-IS authentication ensures that only authorized devices can participate in the routing domain, improving network security.
B. Incorrect.
Using a single large IS-IS area can lead to scalability challenges in large networks, as the routing tables and LSDB (Link State Database) grow significantly.
C. Correct.
The overload bit can be used to manipulate route preference, preventing routers from being used for transit traffic during specific situations such as maintenance.
D. Incorrect.
Disabling metric-based traffic engineering would reduce the flexibility of the IS-IS protocol in optimizing routing decisions, particularly in complex networks.
E. Correct.
Route summarization reduces the size of routing tables, enhances scalability, and limits the propagation of unnecessary updates across IS-IS areas.

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