EIGRP control-plane tables maintained via Hellos/updates: Which EIGRP data structures are kept in RAM and maintained by periodic Hello and triggered update packets?

Introduction / Context:
Enhanced Interior Gateway Routing Protocol (EIGRP) maintains several tables in memory to track neighbors and routes. Understanding which tables exist clarifies how EIGRP forms adjacencies and computes loop-free paths.

Given Data / Assumptions:

• (1) Neighbor table
• (2) STP table
• (3) Topology table
• (4) DUAL table

Concept / Approach:

EIGRP uses Hello packets to discover/maintain neighbors (Neighbor table) and updates/queries to exchange route information (Topology table). The Diffusing Update Algorithm (DUAL) is the algorithm run against the topology table; it is not itself a distinct 'table'. STP is a Layer 2 protocol unrelated to EIGRP.

Step-by-Step Solution:

Verification / Alternative check:

Commands: show ip eigrp neighbors and show ip eigrp topology display these structures. No 'DUAL table' command exists; DUAL results are the successor/feasible successor selections within the topology table.

Why Other Options Are Wrong:

Including STP or a 'DUAL table' introduces items that do not belong to EIGRP’s routing database.

Common Pitfalls:

Confusing DUAL (algorithm) with a data store; mixing Layer 2 STP with Layer 3 routing protocols.

Final Answer:

1 and 3