CCNA IP Routing Practice Question
Which three of the following are valid features of Enhanced Interior Gateway Routing Protocol (EIGRP)? (Choose three.)
⚠ Common exam trap
Cisco often tests the distinction between EIGRP's topology table (which stores all learned routes) and its routing table (which stores only the best routes), and candidates may confuse the 'variance' command with equal-cost load balancing only, forgetting that it enables unequal-cost load balancing.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
EIGRP maintains a topology table containing all routes learned from neighbors.
All three statements are correct features of EIGRP. EIGRP maintains a topology table that stores all routes learned from directly connected neighbors, including feasible successors. It uses the Diffusing Update Algorithm (DUAL) to guarantee loop-free paths by performing a diffusing computation when a route is lost. Additionally, EIGRP supports unequal-cost load balancing by using the 'variance' command, which allows traffic to be distributed across multiple paths with different metrics, as long as the metric of the alternate path is within the variance multiplier times the best metric.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
EIGRP maintains a topology table containing all routes learned from neighbors.
Why this is correct
EIGRP's topology table is a central data structure that stores every route advertised by each directly connected neighbor, including the feasible distance and reported distance for each destination. Only routes that pass feasibility and are loop-free are then considered for installation into the routing table, while the full list remains available for rapid failover.
- ✓
EIGRP uses the Diffusing Update Algorithm (DUAL) to ensure loop-free paths.
Why this is correct
DUAL stands for Diffusing Update Algorithm and operates by performing a diffusing computation across the network when a route changes or becomes unreachable. It ensures a loop-free path at all times through the feasible successor condition, where a neighbor's reported distance must be less than the current feasible distance, thereby eliminating the need for hold-down timers.
- ✓
EIGRP supports unequal-cost load balancing using the 'variance' command.
Why this is correct
The variance command allows EIGRP to install multiple paths to the same destination even when their metrics are not equal, as long as the metric is within the variance multiplier times the best metric. The alternate path must also be a feasible successor to guarantee loop-free routing, and default variance is 1, which restricts load balancing to equal-cost paths only.
- ✗
EIGRP is a link-state routing protocol similar to OSPF.
Why it's wrong here
EIGRP is fundamentally an advanced distance-vector routing protocol, not a link-state protocol like OSPF. Unlike OSPF, it does not build a complete network topology map by flooding LSAs; instead, it exchanges distance-vector information only with directly connected neighbors and relies on DUAL to compute loop-free paths from that limited knowledge.
- ✗
EIGRP uses multicast address 224.0.0.5 for all neighbor communications.
Why it's wrong here
EIGRP's reserved multicast address is 224.0.0.10, not 224.0.0.5; the latter is used by OSPF for Hello packets. Additionally, EIGRP does not rely solely on multicast for all communications because after initial neighbor discovery, it uses unicast RTP (Reliable Transport Protocol) for reliable updates, and multicast is only used on multiaccess networks.
- ✗
EIGRP automatically summarizes routes at classful boundaries by default on all interfaces.
Why it's wrong here
Modern EIGRP implementations have automatic classful summarization disabled by default, and when it is enabled, summarization occurs only at major network classful boundaries, not on every interface. On Cisco IOS versions after 15.0, you must explicitly enable auto-summary, and even then it does not summarize routes at every interface. This option exaggerates both the default behavior and the scope of automatic summarization.
Quick reference
Routing Protocol Comparison
| Protocol | Metric | Max Hops | Algorithm | Type |
|---|---|---|---|---|
| RIP v2 | Hop count | 15 | Bellman-Ford | Distance vector |
| OSPF | Cost (bandwidth) | Unlimited | Dijkstra (SPF) | Link state |
| EIGRP | Composite metric | Unlimited | DUAL | Hybrid |
| IS-IS | Cost | Unlimited | Dijkstra | Link state |
| BGP | Policy / attributes | Unlimited | Path vector | Path vector |
RIP's 15-hop limit makes it unsuitable for large networks. OSPF and EIGRP dominate modern enterprise deployments.
Go deeper
Related to this question
Learn chapter
OSPFv3 Single-Area Configuration for IPv6
Key term
OSPF
OSPF is a link-state routing protocol used to find the best path for data packets to travel across IP networks, like a smart GPS that recalculates routes when traffic changes.
Key term
Metric
A metric is a quantifiable measurement used to assess the performance, health, or status of IT systems, networks, or applications.
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