350-501 Architecture Practice Question
An SP is deploying Inter-AS MPLS VPN option B. Which design characteristic is unique to Option B compared to Option A?
⚠ Common exam trap
Cisco often tests the misconception that Option B requires a full mesh of MP-IBGP sessions (like Option A), when in fact it uses MP-EBGP between ASBRs to eliminate that requirement.
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
✓
ASBRs exchange VPNv4 routes directly via MP-EBGP
In Option B, ASBRs exchange VPNv4 routes directly via MP-EBGP without requiring a full mesh of MP-IBGP sessions between PEs. This eliminates the need for per-VPN VRF configuration on ASBRs, as they only carry labeled VPNv4 routes and perform label allocation per next-hop, not per VPN.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
ASBRs exchange VPNv4 routes directly via MP-EBGP
Why this is correct
Uses MP-EBGP between ASBRs to exchange VPNv4 routes.
- ✗
Requires a full mesh of MP-IBGP sessions between all PEs
Why it's wrong here
Does not require full mesh, Option B uses EBGP between ASBRs.
- ✗
ASBRs maintain separate VRF for each VPN
Why it's wrong here
Does not require VRF on ASBRs.
- ✗
Traffic is forwarded using IP, not MPLS
Why it's wrong here
Uses MPLS labels between ASBRs.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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