This 300-410 practice question tests your understanding of ip sla. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
An engineer configures IP SLA to track a route to a loopback address for BGP next-hop tracking. Router R1 has:
ip sla 4
icmp-echo 192.168.100.1 source-ip 10.0.0.1
frequency 5
ip sla schedule 4 life forever start-time now
track 4 ip sla 4 reachability
router bgp 65001
neighbor 10.0.0.2 remote-as 65002
neighbor 10.0.0.2 update-source Loopback0
neighbor 10.0.0.2 ebgp-multihop 2
neighbor 10.0.0.2 fall-over bfd
But the BGP session to 10.0.0.2 is flapping every 5 seconds. What is the root cause?
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 probe is sending ICMP packets that are being rate-limited by the CoPP policy, causing the BFD session to drop.
The IP SLA probe is sent to 192.168.100.1, but the BGP neighbor is 10.0.0.2. The track is not directly affecting the BGP session. However, the flapping is caused by the BFD session failing because the IP SLA might be interfering with the BFD packets, or more likely, the ebgp-multihop and BFD interaction. The correct answer is that the BFD session is using the same path as the IP SLA, and the IP SLA probe is causing the BFD session to reset due to packet loss or delay.
Key principle: OSPF neighbour adjacency depends on matching area, hello/dead timers, network type, and authentication — IP reachability alone is not enough.
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 probe is sending ICMP packets that are being rate-limited by the CoPP policy, causing the BFD session to drop.
Why this is correct
CoPP might rate-limit ICMP packets, causing the BFD session to fail if BFD relies on the same path and the router's CPU is overwhelmed.
The ebgp-multihop 2 is not sufficient for the BFD session to establish.
Why it's wrong here
EBGP multihop is for BGP, not BFD; BFD can work with multihop if configured correctly.
✗
The update-source Loopback0 is not reachable from 10.0.0.2.
Why it's wrong here
This would prevent BGP from establishing, not cause flapping.
✗
The IP SLA schedule is set to start now, but the frequency is too high, causing the router to crash.
Why it's wrong here
Frequency of 5 seconds is standard and should not cause crashes.
Common exam traps
Common exam trap: OSPF can fail even when IP connectivity looks correct
OSPF neighbour formation depends on matching areas, timers, network type, authentication and passive-interface behaviour. Do not choose an answer only because the devices can ping.
Detailed technical explanation
How to think about this question
OSPF questions usually test the details that control adjacency and route selection. Read the neighbour state, area, router ID and interface configuration before deciding what is wrong.
KKey Concepts to Remember
OSPF neighbours must agree on key parameters.
Router ID selection can affect neighbour relationships and LSDB output.
OSPF cost influences the preferred path.
A route can appear in OSPF information but not become the installed route.
TExam Day Tips
→Check area mismatch first when OSPF adjacency fails.
→Review passive interfaces when a network is advertised but no neighbour forms.
→Use show ip ospf neighbor and show ip route clues carefully.
Key takeaway
OSPF neighbour adjacency depends on matching area, hello/dead timers, network type, and authentication — IP reachability alone is not enough.
Real-world example
How this comes up in practice
A network engineer at a university connects two campus buildings via a fibre link. Both routers run OSPF, but no adjacency forms — even though both routers can ping each other. The engineer finds one router is in area 0 and the other in area 1. OSPF adjacency requires matching area numbers, hello/dead timers, and network type. IP reachability alone is not enough.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this 300-410 question in full detail.
Review OSPF neighbour requirements — matching area type, hello and dead timers, network type, stub flags, and authentication. Study show ip ospf neighbor states (INIT, 2-WAY, FULL). Then practise related 300-410 OSPF questions on adjacency and route selection.
IP SLA — This question tests IP SLA — OSPF neighbours must agree on key parameters..
What is the correct answer to this question?
The correct answer is: The IP SLA probe is sending ICMP packets that are being rate-limited by the CoPP policy, causing the BFD session to drop. — The IP SLA probe is sent to 192.168.100.1, but the BGP neighbor is 10.0.0.2. The track is not directly affecting the BGP session. However, the flapping is caused by the BFD session failing because the IP SLA might be interfering with the BFD packets, or more likely, the ebgp-multihop and BFD interaction. The correct answer is that the BFD session is using the same path as the IP SLA, and the IP SLA probe is causing the BFD session to reset due to packet loss or delay.
What should I do if I get this 300-410 question wrong?
Review OSPF neighbour requirements — matching area type, hello and dead timers, network type, stub flags, and authentication. Study show ip ospf neighbor states (INIT, 2-WAY, FULL). Then practise related 300-410 OSPF questions on adjacency and route selection.
What is the key concept behind this question?
OSPF neighbours must agree on key parameters.
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