PCNE Question 15

Community Discussion

Written by other learners. Comments can disagree with the marked answer — check the official documentation when in doubt.

• Chose A1

  Reason: With BGP, both on-prem routers should advertise unique routes. If both have the same routes and priorities, only one set gets preferred, and traffic won’t be balanced across both VPN tunnels. Since both VPNs connect to a single Cloud Router and only one router’s routes are installed, the overlapping identical routes cause route flapping/preferring one path. Different ASNs (D) are not the issue; having different ASNs is normal for multi-homed setups. Firewalls (B) could block, but the symptom points to identical route advertisements. Load balancing (C) isn’t the cause here; you balance at the network edge via BGP path selection.

• Chose D1

  Reason:The correct answer is D. The ASNs being used on the on-premises routers are different. Cloud Router does not perform Equal-Cost Multi-Path (ECMP) routing across BGP sessions with different Autonomous System Numbers (ASNs). Cloud Router selects the BGP route from the router with the lowest ASN and ignores the routes from the router with the higher ASN. This leads to the observed issue where traffic is not load-balanced, leading to traffic being routed through just one VPN tunnel instead of being load-balanced across both. To resolve this, ensure that both on-premises routers use the same ASN for BGP sessions with Cloud Router

• 3

  Choose D: ASN (Autonomous System Number): An ASN is a unique identifier assigned to an autonomous system for the purpose of routing traffic on the Internet. In BGP (Border Gateway Protocol), each router in a network is assigned a unique ASN. To resolve this issue, ensure that both on-premises routers have the same ASN or use the same ASN for both routers if possible. This will help achieve the desired load balancing across the two VPN connections.