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Difficulty: Very hardAzure Virtual Networks, ExpressRoute, and VPN Gateway

An organization has configured an Azure ExpressRoute circuit as their primary hybrid connection and a Site-to-Site VPN as a backup to the same Azure Virtual Network. Is the statement true or false that Azure automatically routes traffic to the Site-to-Site VPN gateway if the ExpressRoute circuit fails, without requiring any custom User-Defined Routes (UDRs) to be configured?

Answer: Answer

Answer

True
The statement is true because Azure natively supports coexistence of ExpressRoute and VPN gateways. BGP advertisements manage the routing hierarchy, automatically directing traffic to the VPN connection if the primary ExpressRoute path is lost, without any need for User-Defined Routes (UDRs).

Step-by-Step Solution

1
Understand the coexistence setup of Azure ExpressRoute and Site-to-Site VPN on the same Virtual Network.
Both connections advertise on-premises network ranges to Azure, but ExpressRoute has a higher default routing weight/preference.
This establishes ExpressRoute as the primary path and VPN as the backup path.
2
Analyze what happens during an ExpressRoute link failure.
The ExpressRoute routes are withdrawn from the Azure routing table.
BGP dynamically updates the route table when the physical path becomes unavailable.
3
Evaluate the routing decision made by Azure after ExpressRoute route withdrawal.
Azure falls back to the Site-to-Site VPN route that is already propagated via BGP.
No manual route injection or User-Defined Routes (UDRs) are needed because BGP handles the path failover dynamically.

Key Concept

ExpressRoute and Site-to-Site VPN Gateway coexistence and automatic failover
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Topics

Azure Virtual Networks, ExpressRoute, and VPN Gateway

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