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300-410 Practice Question: An engineer configures IP SLA to track a route to…
An engineer configures IP SLA to track a route to a server that is reachable via a GRE tunnel. Router R1 has:
ip sla 9
icmp-echo 172.16.0.1 source-ip 10.0.0.1 frequency 10
ip sla schedule 9 life forever start-time now track 9 ip sla 9 reachability ip route 192.168.2.0 255.255.255.0 Tunnel0 track 9
The GRE tunnel is up, but the route is flapping. Show output on R1:
show interface Tunnel0 Tunnel0 is up, line protocol is up
show track 9
Track 9 IP SLA 9 reachability
Reachability is Up 10 changes, last change 00:00:05
What is the root cause?
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 GRE tunnel has a path MTU issue that causes ICMP packets to be fragmented or dropped, leading to intermittent probe failures.
The IP SLA probe is successful, but the track is flapping. This could be due to the IP SLA probe itself being intermittent, perhaps because the GRE tunnel is using a path that has high latency or packet loss. The correct answer is that the IP SLA probe is being affected by the GRE tunnel's path MTU or fragmentation issues, causing some probes to be dropped.
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 tunnel has a path MTU issue that causes ICMP packets to be fragmented or dropped, leading to intermittent probe failures.
Why this is correct
GRE adds overhead, and if the path MTU is not adjusted, ICMP packets may be dropped due to fragmentation, causing the track to flap.
- ✗
The IP SLA frequency is too high, causing the router to overload.
Why it's wrong here
Frequency of 10 seconds is standard.
- ✗
The source IP 10.0.0.1 is not reachable from the tunnel destination.
Why it's wrong here
The tunnel is up, so reachability is not the issue.
- ✗
The track 9 is not correctly associated with the route.
Why it's wrong here
The association is correct; the flapping is due to the probe.
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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.