Question

Your company has established an HA VPN gateway connecting a Google Cloud VPC to an on-premises data center. Two tunnels are up, each with its own BGP session on the same Cloud Router, and both peers advertise the identical on-premises prefix 10.50.0.0/16 with the same MED value. You want traffic from the VPC toward the on-premises network to be distributed across both tunnels simultaneously to maximize aggregate throughput. What must be true for the Cloud Router to program equal-cost multi-path (ECMP) routes across both tunnels?

Accepted Answer

The two BGP-learned routes for 10.50.0.0/16 must have identical route priority (derived from equal MED values), and both dynamic routes will be installed so traffic is load-shared via ECMP.

Answer

One tunnel must be configured with a lower MED so it becomes primary; ECMP only activates automatically when the primary tunnel's BGP session goes down.

Answer

You must enable a global routing mode on the VPC, because ECMP across VPN tunnels is only supported when Cloud Router advertises routes to all regions.

Answer

You must configure static routes with equal priority pointing to each tunnel, since Cloud Router does not perform ECMP for BGP-learned dynamic routes.