JNCIS-ENT Tunnels Practice Question
You are troubleshooting a GRE tunnel where traceroute shows packets looping between the tunnel endpoints. Which mechanism prevents routing loops in GRE tunnels on Junos?
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
✓
Proper IP routing protocol metric design and TTL decrementing through the encapsulated IP headers.
GRE does not have an inherent TTL field in the GRE header itself, but Junos copies or handles the inner IP header TTL, and enabling keepalives or proper routing protocol design prevents loops. However, MTU and TTL settings are critical. Wait, what about tunnel loop prevention features? Tunnel interfaces rely on proper routing configuration, but let's look at options.
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 GRE header hop-count field dropping packets exceeding 32 hops.
Why it's wrong here
The standard GRE header does not contain a hop-count field.
- ✗
Junos automatically shuts down interfaces when a routing loop is detected.
Why it's wrong here
Junos does not automatically shut down interfaces based on routing loop detection.
- ✗
An automatic split-horizon check built into the GRE driver.
Why it's wrong here
GRE does not have a built-in split-horizon mechanism like distance-vector protocols.
- ✓
Proper IP routing protocol metric design and TTL decrementing through the encapsulated IP headers.
Why this is correct
Routing loops are prevented by proper routing protocol design and IP TTL expiration.
About these practice questions
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Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed August 2026 · checked against the official Juniper Networks exam blueprint
This JNCIS-ENT practice question is part of Courseiva's free Juniper Networks 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 JNCIS-ENT exam.