350-501 Security and Services Practice Question
A service provider wants to prevent IP spoofing at the customer edge by verifying that the source IP address of incoming packets is reachable via the interface they arrive on. Which uRPF mode should be used?
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
✓
Strict mode
Strict mode checks that the source IP is in the FIB and that the best return route is through the same interface. Loose mode only checks that the source IP is in the FIB. Strict mode is used at customer edges where traffic should come from a specific interface.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Strict mode
Why this is correct
Strict mode verifies source IP reachability via the same interface.
- ✗
ACL-based filtering
Why it's wrong here
ACLs are static and not as dynamic as uRPF.
- ✗
Reverse path filtering disabled
Why it's wrong here
Disabling allows spoofing.
- ✗
Loose mode
Why it's wrong here
Loose mode only checks if source IP exists in FIB, not the interface.
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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