300-410 Layer 3 Technologies Practice Question
A network engineer is troubleshooting a Cisco IOS XE router running OSPFv2. The router is an ABR between Area 0 and Area 1. Area 1 is configured as a Not-So-Stubby Area (NSSA). The engineer notices that a Type-7 LSA originated by an ASBR in Area 1 is not being translated into a Type-5 LSA by the ABR. Which condition would prevent the ABR from performing Type-7 to Type-5 translation?
⚠ Common exam trap
The trap here is focusing on ABR election or forwarding address issues, when the P-bit in the Type-7 LSA is the direct control for whether translation occurs.
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 Type-7 LSA has the P-bit (Propagate bit) cleared, indicating that the LSA should not be translated by the ABR.
Type-7 to Type-5 translation in an NSSA depends on the P-bit in the Type-7 LSA. If the P-bit is cleared, the ABR will not translate the LSA into a Type-5 LSA, preventing the external route from being propagated into the backbone area. This bit is set by the originating ASBR and can be cleared in specific scenarios.
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 ABR has a static route to the NSSA ASBR's loopback interface but no OSPF adjacency with the ASBR.
Why it's wrong here
The ABR does not need an OSPF adjacency with the ASBR to translate Type-7 LSAs. Translation is based on the LSA contents and the P-bit, not on adjacency state. A static route to the ASBR's loopback is irrelevant for translation. The ABR only needs to be an ABR for the NSSA and have the Type-7 LSA in its LSDB with the P-bit set.
- ✗
The ABR is not configured with the `area 1 nssa translate type7 always` command and there is another ABR with a higher router ID in the NSSA.
Why it's wrong here
Without the `always` keyword, the ABR with the highest router ID among NSSA ABRs performs translation. If another ABR has a higher router ID, this ABR correctly does not translate. However, the scenario states the engineer expects this ABR to translate; the question asks what would prevent translation. The absence of `always` is normal behavior, not a fault, unless the other ABR is unable to translate. This is not the definitive preventing condition here.
- ✓
The Type-7 LSA has the P-bit (Propagate bit) cleared, indicating that the LSA should not be translated by the ABR.
Why this is correct
In NSSA, the P-bit in the Type-7 LSA options field indicates whether the LSA should be translated into a Type-5 LSA by the ABR. If the P-bit is cleared, the ABR will not translate the LSA. The P-bit is typically set by the ASBR when the LSA is originated, but it can be cleared under certain conditions, such as when the ASBR is also an ABR or when the LSA is redistributed without the proper configuration. This directly prevents translation.
- ✗
The forwarding address in the Type-7 LSA is set to 0.0.0.0 and the ABR has no route to the ASBR's router ID.
Why it's wrong here
A forwarding address of 0.0.0.0 in a Type-7 LSA means the translator should use the originating router's interface address as the next hop. The ABR does not need a route to the ASBR's router ID for translation; it needs reachability to the forwarding address or the originating router. This condition alone does not prevent translation.
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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Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official Cisco exam blueprint
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