The answer is to set BGP community 79ba:100 on routes from the preferred interconnect. This is correct because Google Cloud interprets the 16-bit ASN format community 79ba:100 (decimal 31210:256) as a signal to increase the local preference of those routes on the Cloud Router, making the closer interconnect the preferred path for outbound traffic to on-premises. In BGP route selection, higher local preference is evaluated before MED or AS-path length, so this community directly influences the interconnect route selection. On the Google Professional Cloud Network Engineer exam, this tests your understanding of how Google-defined BGP communities override default routing behavior without requiring complex policy configuration. A common trap is confusing this with MED or standard AS-path prepending, but remember that 79ba:100 is a Google-specific community that manipulates local preference, not path attributes. Memory tip: think “79ba:100 = Prefer the closer” — the hex “79ba” sounds like “prefer,” and the “100” signals a higher preference value.
PCNE Implementing hybrid interconnectivity Practice Question
This PCNE practice question tests your understanding of implementing hybrid interconnectivity. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. 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.
A company has two Dedicated Interconnects in different metro regions connecting to Google Cloud. They want to use BGP communities to influence Cloud Router's route selection to prefer the closer interconnect for outbound traffic to on-premises. Which community action can they apply on the on-premises routers?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Set BGP community 79ba:100 on routes from the preferred interconnect
Option C is correct because Google Cloud uses 16-bit ASN format for BGP communities, and the well-known community 79ba:100 (equivalent to 31210:256 in decimal) is a Google-defined community that sets a higher local preference on routes received from the preferred interconnect. This influences Cloud Router's route selection to prefer the closer interconnect for outbound traffic to on-premises, as higher local preference is evaluated before MED or AS-path length.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
Set BGP community 2:100 on routes to indicate MED change
Why it's wrong here
No such standard community; MED is set directly, not via community.
✗
Set BGP community 0:100 on routes to mark them as high preference
Why it's wrong here
Custom communities are not used by Cloud Router for route selection.
✓
Set BGP community 79ba:100 on routes from the preferred interconnect
Why this is correct
The community 79ba:100 (lowest RTT) is supported by Google's Cloud Router to influence route preference for outbound traffic.
Related concept
Read the scenario before looking for a memorised answer.
✗
Set BGP community 79ba:101 on routes from the preferred interconnect
Why it's wrong here
79ba:101 is not a recognized Google community for path selection.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Google Cloud often tests the specific Google-defined BGP community format (79ba:xxxx) and its meaning, so candidates may confuse it with standard 2-byte communities or assume any community value works, leading them to pick generic options like 2:100 or 0:100.
Detailed technical explanation
How to think about this question
Google Cloud's BGP communities use the private ASN 31210 (hex 79ba) and the second half of the community value encodes the preference level: 100 (decimal 256) for high, 101 (decimal 257) for medium, and 102 (decimal 258) for low. When Cloud Router receives routes with community 79ba:100, it automatically assigns a local preference of 1000 (high), overriding the default 100, which ensures that routes from the preferred interconnect are chosen for outbound traffic before considering other path attributes.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
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
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Cloud exam questions reward reading the constraint carefully: the same technology can be right or wrong depending on the use case.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Implementing hybrid interconnectivity — This question tests Implementing hybrid interconnectivity — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Set BGP community 79ba:100 on routes from the preferred interconnect — Option C is correct because Google Cloud uses 16-bit ASN format for BGP communities, and the well-known community 79ba:100 (equivalent to 31210:256 in decimal) is a Google-defined community that sets a higher local preference on routes received from the preferred interconnect. This influences Cloud Router's route selection to prefer the closer interconnect for outbound traffic to on-premises, as higher local preference is evaluated before MED or AS-path length.
What should I do if I get this PCNE question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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