CISCO 300-420 Designing Cisco Enterprise Networks (ENSLD) Exam Free Practice Test — 30 Questions
This practice bank tests your understanding of enterprise campus network design and routing protocol optimization. You will analyze Layer 2/3 boundary placement considerations, including STP and VLAN trunking for loop prevention and efficiency. Routing protocol questions cover EIGRP metric tuning (bandwidth/delay, K-values), OSPF multi-area design (ABR, stub/totally stubby areas), and IS-IS hierarchy (Level-1/2 routers) with wide metrics for fast convergence. Master these topics to make informed design decisions that balance scalability, redundancy, and performance in real-world enterprise networks.
What this 300-420 practice set measures
This is an analysis of the practice bank, not a claim about the vendor's live exam blueprint. Use it to identify the knowledge, judgment, and recall patterns exercised here, then verify your coverage against the current official exam guide.
Campus Network Design: Layer 2/3 Boundaries and STP
The practice bank emphasizes placing the Layer 3 boundary at either the distribution or access layer, each with distinct trade-offs. A distribution-layer boundary balances routing efficiency and broadcast domain size, while an access-layer boundary minimizes broadcast domains but increases routing complexity. For Layer 2 designs, Spanning Tree Protocol (STP) variants such as RSTP are critical for loop prevention and rapid convergence. VLAN trunking optimizes bandwidth by allowing multiple VLANs over a single link. These decisions directly impact network performance and fault isolation.
- Distribution-layer Layer 3 boundary improves scalability and fault isolation.
- Access-layer Layer 3 boundary reduces broadcast domain size.
- RSTP provides faster convergence than legacy STP in redundant topologies.
- VLAN trunking maximizes link utilization and simplifies VLAN management.
EIGRP Design: Metrics and Loop-Free Path Selection
EIGRP uses bandwidth and delay by default for its composite metric, stored in the topology table alongside all known routes. The feasibility condition ensures loop-free paths by comparing advertised distances. Adjusting K-values allows preference for lower delay, as in Mr. Davis's scenario. Understanding these mechanisms is key to troubleshooting suboptimal routing, like Ms. Clark's issue, where verifying interface bandwidth and delay settings is essential. DUAL (Diffusing Update Algorithm) is EIGRP's unique convergence algorithm.
- Default EIGRP metric combines bandwidth and delay (K1=1, K3=1).
- The feasibility condition prevents routing loops by accepting only feasible successors.
- Topology table stores all known routes; the routing table contains best paths.
- Adjust K-values to prioritize delay over bandwidth for path selection.
OSPF Multi-Area Design: Area Types and Routers
OSPF uses Hello packets to establish neighbor relationships and relies on ABRs to connect areas to the backbone (Area 0). Stub areas block external LSAs (Type 5), reducing routing table size and improving stability. Totally stubby areas go further by also blocking summary LSAs (Type 3). These area types are ideal for minimizing the impact of topology changes, as Ms. Green's scenario shows. OSPF's fast convergence and scalability make it suitable for large networks.
- ABRs route between areas and inject summary LSAs into the backbone.
- Stub areas prevent external LSAs, relying on a default route for external destinations.
- Totally stubby areas block both external and summary LSAs for maximum route reduction.
- Hello packets maintain neighbor relationships and support DR/BDR election on broadcast networks.
IS-IS Design: Hierarchy and Wide Metrics
IS-IS operates at Layer 2, unlike OSPF which runs over IP. Level-1 routers handle intra-area routing, while Level-2 routers interconnect areas. For large enterprises with multiple geographic locations, Level-2 routers are essential. Wide metrics (extended style) allow for more granular cost values, essential for fast convergence in scalable networks. Ms. Blue's design should prioritize wide metrics to efficiently handle modern link speeds and path diversity.
- IS-IS Level-1 routers are aware only of their area; Level-2 routers form the backbone.
- Wide metrics support values up to 2^24-1, enabling precise cost assignment.
- IS-IS runs directly over the data link layer, independent of IP.
- Use Level-2 routers to interconnect areas in a multi-location network.
Practice CISCO 300-420 Designing Cisco Enterprise Networks (ENSLD) Exam with real flashcards
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Where is the recommended placement of the Layer 3 boundary in a modern enterprise campus network?
Study workflow
Turn one 300-420 attempt into a study plan
- 1
Identify Layer 3 Boundary Placement
Assess the campus size and redundancy needs. For a multi-floor building like Mr. Johnson's, place the Layer 3 boundary at the distribution layer to balance broadcast domains and routing efficiency. For smaller networks needing minimal broadcast domains, consider the access layer but account for increased routing overhead.
- 2
Configure Rapid Spanning Tree Protocol
When rapid convergence is critical (Mr. Johnson's scenario), enable RSTP on all switches. RSTP reduces convergence time to seconds by using port roles and proposal-agreement handshakes. Ensure all switches support RSTP and disable legacy STP to avoid incompatibility.
- 3
Tune EIGRP Metrics Using K-Values
To prioritize paths with lower delay (Mr. Davis's case), adjust EIGRP K-values. By default K1=1 and K3=1. Set K3=0 to ignore delay, or adjust K1 and K3 weights. Use the 'metric weights' command under router EIGRP, and verify with 'show ip eigrp topology'.
- 4
Design OSPF Stub Areas for Route Reduction
To prevent external LSAs (Mr. Green's requirement), configure stub areas. On the ABR, use 'area X stub' command. For totally stubby areas (Ms. Green's scenario), add 'no-summary' to block summary LSAs. Verify with 'show ip ospf database'.
- 5
Implement IS-IS Wide Metrics
For fast convergence in large networks (Ms. Blue's design), enable wide metrics using 'metric-style wide' under router IS-IS. This allows values up to 2^24-1. Reconfigure all interfaces with appropriate costs and verify with 'show isis interface'.
FAQ
Questions about this 300-420 practice page
Clear boundaries on what the bank covers, how to use it, and where official vendor information still matters.
What is the main difference between OSPF stub and totally stubby areas?+
A stub area blocks Type 5 external LSAs but allows Type 3 summary LSAs. A totally stubby area blocks both Type 5 and Type 3 LSAs, injecting only a default route. This further reduces the routing table size and limits topology change propagation, ideal for areas with limited routing resources.
Why does EIGRP's DUAL algorithm ensure loop-free paths?+
DUAL uses the feasibility condition: a path is accepted as a feasible successor only if the reported distance (RD) from the neighbor is less than the current feasible distance (FD). This guarantees that the alternate path does not loop back to the router itself, ensuring loop-free routing.
When should you place the Layer 3 boundary at the access layer versus the distribution layer?+
Place it at the access layer when minimizing broadcast domain size is critical, such as in networks with many end hosts needing fault isolation. Use distribution layer for better scalability and simpler routing, as it aggregates access switches and reduces the number of routing peers.
How does IS-IS differ from OSPF in terms of network layer dependency?+
IS-IS runs directly over the data link layer (Layer 2), making it protocol-independent and able to route IP, IPv6, and other protocols. OSPF runs over IP (Layer 3) and uses IP protocol number 89, so it requires IP connectivity between routers.
What is the benefit of using RSTP over STP in a campus network?+
RSTP provides faster convergence (typically <1 second) by actively negotiating transitions between port states instead of relying on timers. It also introduces edge and alternate port roles, making it suitable for networks requiring minimal downtime during topology changes, as in Mr. Johnson's design.
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