350-401 Question 355
Single answerA network engineer is troubleshooting a routing issue in a multi-vendor network. They observe that a route is being learned through two different paths in their EIGRP domain, but one of the paths is consistently preferred despite having a higher metric. Further investigation reveals that the less-preferred path has a route tag applied. What loop prevention mechanism is most likely causing this behavior?
- A
Split Horizon
- B
Route Tagging
- C
Route Poisoning
- D
Filtering
Show answer and explanation
Correct answer: B
Explanation
The observed behavior indicates that a loop prevention mechanism is influencing route selection. Specifically, the application of a route tag is deprioritizing one of the paths. Route tagging is commonly used in EIGRP and other protocols to influence path selection by marking routes with metadata. This ensures loops are avoided by preventing certain tagged routes from being selected as the best path.
- A. Incorrect.
Split Horizon prevents a router from advertising a route back out of the interface from which it was learned. This is not related to the use of a route tag in this scenario.
- B. Correct.
Route Tagging is a loop prevention mechanism where additional metadata (tags) is applied to routes. These tags can influence route selection by marking routes as less desirable or even invalid, which matches the behavior observed in this scenario.
- C. Incorrect.
Route Poisoning involves marking a route as unreachable by setting its metric to an infinite value (e.g., 16 in RIP). This does not align with the observed behavior, where the route is still being learned but simply deprioritized.
- D. Incorrect.
Filtering involves explicitly permitting or denying routes based on criteria such as prefix, but the question does not mention any filtering configuration being applied.