Which BGP Attribute Controls Active/Passive Hybrid Egress?

Your organization wants to set up hybrid connectivity with VLAN attachments that terminate in a single Cloud Router with 99.9% uptime. You need to create a network design for your on-premises router that meets those requirements and has an active/passive configuration that uses only one VLAN attachment at a time. What should you do?

Create a design that uses the LOCAL_PREF BGP attribute to influence the egress path from Google Cloud to the on-premises environment.
Create a design that uses an equal-cost multipath (ECMP) with flow-based hashing on your on-premises devices.
Create a design that uses a BGP multi-exit discriminator (MED) attribute to influence the egress path from Google Cloud to the on-premises environment. Source Reference Answer
Create a design that uses the AS_PATH BGP attribute to influence the egress path from Google Cloud to the on-premises environment.

Community Votes

56%

44%

56% of anonymous learners picked answer C. Votes are pick records left by other test-takers — they are not the verified answer.

Community Insight

Tests precise knowledge of BGP attribute scope, with the common trap being the misapplication of LOCAL_PREF to external peer routing instead of its correct internal AS usage.

This PCNE practice question focuses on selecting the correct BGP attribute to manage hybrid cloud traffic flow with active/passive VLAN attachments. The community consensus confirms that MED is the standard mechanism for influencing inbound traffic from Google Cloud while maintaining strict path preference.

Option A (LOCAL_PREF) is frequently chosen because candidates assume higher-priority attributes always dictate routing; however, LOCAL_PREF is strictly confined to iBGP sessions within a single autonomous system and cannot influence Google Cloud’s routing decisions.

Community Discussion (7 comments)

mohitms1996 👍 1 Selected: C

You're absolutely right! Local Preference (LOCAL_PREF) is a BGP attribute used to influence egress traffic within the same Autonomous System (AS). It helps on-premises routers decide which path to use when sending traffic to Google Cloud. However, in the given scenario, we need to influence Google Cloud’s egress path to on-premises. Multi-Exit Discriminator (MED) is the preferred attribute for this because it influences the egress traffic from Google Cloud towards on-premises.

RKS_2021 👍 1 Selected: C

Changing answer to C

rich_maverick 👍 1 Selected: A

A is correct. MED is a negotiated attribute between routers and is not guaranteed. Local Preference has higher priority than MED.

1f01b87 👍 1 Selected: C

The BGP multi-exit discriminator (MED) attribute is used in BGP configurations to influence the choice of path in an active/passive setup by prioritizing one path over another for egress traffic. This is ideal for a design that uses only one VLAN attachment at a time.

1f01b87 👍 2 Selected: C

It's C as per this google doc. https://cloud.google.com/network-connectivity/docs/interconnect/how-to/dedicated/configuring-onprem-routers#configuring-devices-for-activepassive-forwarding

RKS_2021 👍 1 Selected: A

A is correct

b0b25 👍 2 Selected: A

Local Preference is used to influence egress traffic within an Autonomous System (AS). It determines which exit point to use for outbound traffic

Comments & Corrections

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Expert Analysis

Why the Answer Is Correct

The Multi-Exit Discriminator (MED) is explicitly designed to suggest a preferred entry point to external autonomous systems, making it the ideal choice for controlling how Google Cloud routes traffic back to your on-premises data center. By advertising routes with lower MED values on the primary VLAN attachment and higher values on the secondary, you enforce an active/passive model where only one path is utilized at a time. This aligns directly with Google Cloud’s documented best practices for dedicated interconnect failover scenarios.

Why the Other Options Are Wrong

LOCAL_PREF (Option A) is an internal BGP attribute that only affects route selection within your own autonomous system, so it cannot influence Google Cloud’s egress behavior. ECMP (Option B) inherently creates active/active load balancing, which directly violates the requirement to use only one VLAN attachment at a time. AS_PATH manipulation (Option D) is primarily used for loop prevention and basic path length comparison rather than granular traffic engineering for hybrid connectivity.

Community Comment Notes

The voting split closely mirrors real-world candidate confusion, with 56 votes for MED and 44 for LOCAL_PREF. Multiple users initially debated whether LOCAL_PREF’s higher priority overrides MED, but clarified that cross-network influence requires MED. Comment [1] successfully pointed to the official Google documentation confirming MED configuration for active/passive forwarding. Comment [3] accurately noted that while LOCAL_PREF guides internal exit points, MED is required to steer inbound traffic from partner clouds.

Official Reference

https://cloud.google.com/network-connectivity/docs/interconnect/how-to/dedicated/configuring-onprem-routers#configuring-devices-for-activepassive-forwarding

Exam Strategy

Memorize the directional scope of key BGP attributes: LOCAL_PREF governs internal outbound routing, MED dictates external inbound routing, and AS_PATH handles loop prevention. When encountering hybrid cloud design questions, immediately filter out active/active options if the prompt specifies active/passive or single-path requirements.

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