hardMultiple ChoiceObjective-mapped
300-410 Practice Question: An engineer configures mutual redistribution…
An engineer configures mutual redistribution between OSPF and EIGRP on a router. After configuration, routing loops occur. Which is the most likely explanation?
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 administrative distance of the redistributed routes is not modified, causing the redistributed route to be preferred over the original.
Mutual redistribution without route tagging or filtering can cause routing loops. When a route redistributed from OSPF into EIGRP is then redistributed back into OSPF, it can be preferred over the original route if the administrative distance is lower, creating a loop. This is a classic edge case that requires careful use of route tags and distribute-lists.
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 administrative distance of the redistributed routes is not modified, causing the redistributed route to be preferred over the original.
Why this is correct
Without adjusting the administrative distance (e.g., using 'distance' command on redistributed routes), the redistributed route may have a lower AD than the original, leading to a routing loop.
- ✗
The seed metric is not configured for EIGRP redistribution.
Why it's wrong here
Missing seed metric would prevent EIGRP from accepting the redistributed routes, not cause loops.
- ✗
The OSPF process ID is mismatched.
Why it's wrong here
Mismatched process ID would prevent OSPF from working altogether, not cause loops.
- ✗
The redistribute command is missing the subnets keyword.
Why it's wrong here
Missing the subnets keyword would only redistribute classful networks, not cause loops.
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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Same concept, more angles
1 more way this is tested on 300-410
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A redistribution setup between OSPF and EIGRP is causing a routing loop for subnet 10.1.1.0/24. Router R1 runs OSPF and EIGRP with redistribution. R1's configuration: router ospf 1 redistribute eigrp 100 subnets ! router eigrp 100 redistribute ospf 1 metric 10000 100 255 1 1500 ! interface GigabitEthernet0/0 ip address 10.1.1.1 255.255.255.0 ip summary-address eigrp 100 10.1.0.0 255.255.255.0 ! Router R2 (EIGRP neighbor) shows: R2# show ip route 10.1.1.0 Routing entry for 10.1.0.0/24, supernet Known via "eigrp 100", distance 90, metric 30720, type internal Last update from 10.1.1.1 on GigabitEthernet0/0, 00:00:05 ago What is the root cause?
hard- ✓ A.The summary route 10.1.0.0/24 is less specific and can cause routing loops when combined with redistribution because R2 may send traffic for 10.1.1.0/24 back to R1.
- B.The redistribution metric is too high, causing EIGRP to prefer the OSPF route via another path.
- C.OSPF does not support subnets keyword, so the route is not redistributed correctly.
- D.EIGRP is not enabled on the interface, so the summary is not advertised.
Why A: The summary route 10.1.0.0/24 is being advertised via EIGRP, but it is a less specific prefix than the actual /24. When R1 redistributes OSPF into EIGRP, the summary may cause R2 to prefer the summary over a more specific route, and if R2 sends traffic back to R1 for 10.1.1.0/24, R1 might forward it to R2 again if the OSPF route is not present, creating a loop. The summary should match the exact subnet or be more specific to avoid loops.
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.