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300-410 Practice Question: In a VRF-Lite network, redistribution is…
In a VRF-Lite network, redistribution is configured between OSPF and EIGRP. The engineer notices that some routes are being redistributed in a loop, causing instability. The network uses route tagging, but the loop persists. 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 seed metric for EIGRP is set to a low value (e.g., 1), causing the redistributed route to be preferred over the original OSPF route, leading to a loop.
Mutual redistribution can cause routing loops if routes are not properly tagged and filtered. However, even with tags, if the seed metric is not set correctly, the redistributed route may have a lower metric than the original, causing it to be preferred and re-redistributed. The edge case here is that the seed metric for EIGRP (default is infinity) must be set, but if set too low, it can cause loops. Additionally, if the same prefix exists in both protocols, the administrative distance comparison may cause the redistributed route to be preferred over the original, leading to a loop.
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 route tag is not being propagated correctly because OSPF uses a 32-bit tag and EIGRP uses a 32-bit tag, but the tag is lost during redistribution.
Why it's wrong here
Both OSPF and EIGRP support 32-bit tags, and tags are preserved across redistributions if configured properly.
- ✓
The seed metric for EIGRP is set to a low value (e.g., 1), causing the redistributed route to be preferred over the original OSPF route, leading to a loop.
Why this is correct
If the seed metric is too low, the redistributed route may have a lower composite metric than the original, causing it to be selected and re-redistributed, creating a loop.
- ✗
The administrative distance of OSPF (110) is lower than EIGRP (90), so the redistributed route is always preferred.
Why it's wrong here
EIGRP has a lower AD (90) than OSPF (110), so EIGRP routes are preferred. This can cause loops, but the issue is more about metric than AD.
- ✗
The 'redistribute connected' command is used under OSPF, which redistributes all connected interfaces, including the loopback used for router ID.
Why it's wrong here
Redistributing connected interfaces can cause issues, but it is not the primary cause of a loop in mutual redistribution.
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.
Go deeper
Related to this question
Learn chapter
Introduction to ENARSI Exam and Network Fundamentals
Key term
MPLS Layer 3 VPN
A technology that uses Multiprotocol Label Switching to create secure, scalable virtual private networks that connect multiple sites at the network layer, where the service provider manages routing between customer sites.
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