hardMultiple ChoiceObjective-mapped
300-410 Practice Question: A large enterprise uses IP SLA to track a route…
A large enterprise uses IP SLA to track a route to a remote site via an MPLS L3VPN. Router R1 (PE) has:
ip sla 8
icmp-echo 10.10.10.10 source-ip 192.168.1.1 frequency 10
ip sla schedule 8 life forever start-time now track 8 ip sla 8 reachability ip route vrf CUSTOMER 10.10.10.0 255.255.255.0 192.168.1.2 track 8
The MPLS network is operational, but the route is intermittently removed. Show output on R1:
show ip route vrf CUSTOMER 10.10.10.0 Routing entry for 10.10.10.0/24 Known via "static", distance 1, metric 0 Last update from 192.168.1.2 on GigabitEthernet0/0
* 192.168.1.2, via GigabitEthernet0/0
But the track is down:
show track 8
Track 8 IP SLA 8 reachability
Reachability is Down 3 changes, last change 00:00:15
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 IP SLA is not configured with the vrf CUSTOMER keyword, so the probe is sent in the global table and cannot reach the target in the VRF.
The IP SLA probe is sent to 10.10.10.10, but the source IP is 192.168.1.1. In an MPLS L3VPN, the VRF CUSTOMER might have a different routing table. The probe is sent in the global table unless configured with vrf. The correct answer is that the IP SLA is not VRF-aware, so the probe fails, but the static route is still installed because the track is down but the route is not removed immediately due to the delay or because the route is still in the table from a previous state.
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 IP SLA is not configured with the vrf CUSTOMER keyword, so the probe is sent in the global table and cannot reach the target in the VRF.
Why this is correct
The IP SLA must be VRF-aware to send probes within the VRF; otherwise, the probe fails and the track goes down, but the route might still be installed due to other factors.
- ✗
The MPLS label distribution is failing, causing the IP SLA probe to be dropped.
Why it's wrong here
The MPLS network is operational per the scenario.
- ✗
The source IP 192.168.1.1 is not in the VRF CUSTOMER, so the probe cannot be sourced correctly.
Why it's wrong here
The source IP can be in the global table; the issue is the probe is not sent in the VRF.
- ✗
The track 8 is not supported for VRF routes.
Why it's wrong here
Track with IP SLA is supported for VRF routes if configured correctly.
Go deeper
Related to this question
Learn chapter
Introduction to ENARSI Exam and Network Fundamentals
Key term
LDP Protocol
LDP, or Label Distribution Protocol, is a protocol that routers use to automatically exchange labels that enable MPLS (Multiprotocol Label Switching) to create fast, efficient paths for data packets across a network.
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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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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