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300-410 Practice Question: Two OSPF domains are redistributed into each…
Two OSPF domains are redistributed into each other on router R1. R1 has:
router ospf 1
redistribute ospf 2 subnets
router ospf 2
redistribute ospf 1 subnets
Router R2 (in OSPF 1) shows: R2# show ip route ospf
O E2 10.1.1.0/24 [110/20] via 10.2.1.1, 00:00:05, Serial0/0/0 O E2 10.2.1.0/24 [110/20] via 10.2.1.1, 00:00:05, Serial0/0/0
R2# traceroute 10.1.1.1 source 10.2.1.2
Type escape sequence to abort. Tracing the route to 10.1.1.1 1 10.2.1.1 4 msec 4 msec 4 msec 2 10.1.1.1 8 msec 8 msec 8 msec
R2# traceroute 10.2.1.1 source 10.1.1.2
Type escape sequence to abort. Tracing the route to 10.2.1.1 1 10.1.1.1 4 msec 4 msec 4 msec 2 10.2.1.1 8 msec 8 msec 8 msec Traffic between the two domains is taking suboptimal paths. What is the root cause?
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
✓
The redistribution is mutual without any route filtering, causing routing loops.
Mutual redistribution without route filtering creates a routing loop. Routes from OSPF 1 are redistributed into OSPF 2, and then back into OSPF 1, causing suboptimal paths. The traceroute shows traffic going through R1 twice. The fix is to use route tagging and filtering to prevent re-redistribution.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
The redistribution is mutual without any route filtering, causing routing loops.
Why this is correct
Routes from OSPF 1 are redistributed into OSPF 2 and then back into OSPF 1, creating a loop.
- ✗
The 'subnets' keyword is missing from one of the redistribute commands.
Why it's wrong here
Both redistribute commands include 'subnets'.
- ✗
OSPF administrative distance is set incorrectly, preferring external routes.
Why it's wrong here
The default AD for OSPF external routes is 110, which is not causing the loop.
- ✗
R1 has a routing table entry for 10.1.1.0/24 pointing to R2.
Why it's wrong here
The traceroute shows R1 as the next hop, not R2.
Visual reference
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.
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 300-410 practice question is part of Courseiva's free Cisco certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 300-410 exam.