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300-410 Practice Question: In DMVPN Phase 3, which loop prevention mechanism…
In DMVPN Phase 3, which loop prevention mechanism is used by default to prevent routing loops when using EIGRP?
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
✓
Feasibility Condition
EIGRP uses the Feasibility Condition (FC) as its loop prevention mechanism. In DMVPN Phase 3, with EIGRP stub routing and summarization, the FC ensures that only feasible successors are used, preventing loops. Additionally, the 'no ip split-horizon' is often required on the hub, but loop prevention relies on EIGRP's DUAL algorithm and the FC.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Split horizon
Why it's wrong here
Incorrect. Split horizon is disabled by default on tunnel interfaces in DMVPN to allow hub to advertise routes back to spokes.
- ✗
Route poisoning
Why it's wrong here
Incorrect. Route poisoning is used in RIP, not EIGRP.
- ✓
Feasibility Condition
Why this is correct
Correct. EIGRP's DUAL algorithm uses the Feasibility Condition to prevent loops.
- ✗
Hold-down timers
Why it's wrong here
Incorrect. Hold-down timers are used in RIP, not EIGRP.
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
OSPF Route Summarization and Filtering
Key term
DMVPN Phase 3
DMVPN Phase 3 is a Cisco networking technology that allows branch offices to connect directly to each other without always going through a central hub, but with smarter routing that lets the hub control the traffic paths more efficiently.
Key term
EIGRP Stub Routing
EIGRP stub routing is a feature that restricts a router from learning routes from neighbors and limits the routes it advertises, improving network stability and reducing resource usage in remote or spoke locations.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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