This PCNE practice question tests your understanding of customlearnedroutepriority. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. A key principle to apply: customLearnedRoutePriority. 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.
Refer to the exhibit. The Cloud Router is connected to two on-premises routers via dedicated interconnect. The on-premises routers advertise the same prefix 10.1.0.0/16. Which on-premises router's route will be preferred by Google Cloud for traffic destined to 10.1.0.0/24? (Assume equal AS path length and MED from on-premises.)
The answer is the route from the peer with IP 169.254.1.1. Google Cloud Router’s BGP best path selection uses a deterministic tie-breaker when all other attributes—like AS path length and MED—are equal: it prefers the route with the higher link-local (peer) IP address. Since 169.254.1.1 is numerically greater than 169.254.0.1, that peer’s route wins for traffic destined to 10.1.0.0/24. On the Google Professional Cloud Network Engineer exam, this scenario tests your understanding of Cloud Router’s unique tie-breaking logic for Dedicated Interconnect or Partner Interconnect with multiple VLAN attachments. A common trap is assuming a lower IP is preferred, as in traditional BGP, but Google Cloud inverts this rule. Remember the memory tip: “Higher IP, higher priority”—think of the peer IP as a score where the bigger number takes the traffic.
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 route from peer with IP 169.254.1.1
Google Cloud Router uses the customLearnedRoutePriority attribute as a tiebreaker when two on-premises routers advertise the same prefix via separate VLAN attachments on Dedicated Interconnect, assuming equal AS path length and MED. The router with the lower customLearnedRoutePriority value is preferred. In this scenario, the peer 169.254.1.1 has a lower priority (e.g., 100) compared to 169.254.0.1's higher priority (e.g., 200). Therefore, the route from peer 169.254.1.1 is selected.
Key principle: customLearnedRoutePriority
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 route with lower peer IP address
Why it's wrong here
Peer IP address does not affect route preference.
✗
Both routes will be used equally (ECMP)
Why it's wrong here
Different priorities prevent ECMP.
✗
The route from peer with IP 169.254.0.1
Why it's wrong here
This peer has customLearnedRoutePriority 200, which is higher (less preferred).
✓
The route from peer with IP 169.254.1.1
Why this is correct
This peer has customLearnedRoutePriority 100, which is lower (more preferred).
Related concept
customLearnedRoutePriority
Common exam traps
Common exam trap: answer the scenario, not the keyword
A common pitfall is to assume that BGP uses the lowest neighbor IP address as a tiebreaker when AS path length and MED are equal. In Google Cloud, however, Cloud Router uses the customLearnedRoutePriority attribute (lower is preferred) for routes learned from different VLAN attachments on Dedicated Interconnect. The priority is configured per VLAN attachment and is independent of the peer IP. Therefore, the correct answer is not based on the IP address; it depends on which VLAN attachment has the lower priority value. Candidates must recognize that the IP addresses given are just identifiers, and the tiebreaker is a non-standard BGP attribute specific to Google Cloud.
Detailed technical explanation
How to think about this question
Google Cloud Router implements a modified BGP best-path selection algorithm that, after comparing standard attributes (weight, local preference, AS path, MED, eBGP vs iBGP), uses the highest BGP identifier (router ID) as a tiebreaker. However, for VLAN attachments on Dedicated Interconnect, the link-local IP addresses (169.254.x.x) serve as the BGP identifiers, so the route from the peer with the higher link-local IP is preferred. This ensures deterministic behavior without relying on ECMP, which could cause asymmetric routing or suboptimal failover in hybrid cloud scenarios.
KKey Concepts to Remember
customLearnedRoutePriority
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
customLearnedRoutePriority
Real-world example
How this comes up in practice
A cloud solutions architect for a retail company is evaluating services for a new workload. The correct answer here reflects best practice for the specific scenario described — not a general cloud recommendation. customLearnedRoutePriority Cloud exam questions reward reading the constraint carefully: the same technology can be right or wrong depending on the use case.
Visual reference
What to study next
Got this wrong? Here's your next step.
Review customLearnedRoutePriority, then practise related PCNE questions on the same topic to reinforce the concept.
The correct answer is: The route from peer with IP 169.254.1.1 — Google Cloud Router uses the customLearnedRoutePriority attribute as a tiebreaker when two on-premises routers advertise the same prefix via separate VLAN attachments on Dedicated Interconnect, assuming equal AS path length and MED. The router with the lower customLearnedRoutePriority value is preferred. In this scenario, the peer 169.254.1.1 has a lower priority (e.g., 100) compared to 169.254.0.1's higher priority (e.g., 200). Therefore, the route from peer 169.254.1.1 is selected.
What should I do if I get this PCNE question wrong?
Review customLearnedRoutePriority, then practise related PCNE questions on the same topic to reinforce the concept.
What is the key concept behind this question?
customLearnedRoutePriority
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Question Discussion
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