Answer: Layer 3

Azure ExpressRoute primarily operates at Layer 3 (Network Layer) of the OSI model. This is supported by Microsoft's official documentation, which states that ExpressRoute provides Layer 3 connectivity between on-premises networks and Microsoft Cloud through connectivity providers. ExpressRoute uses IP routing and BGP (Border Gateway Protocol) for dynamic route exchange, which are Layer 3 functions. While some comments mention Layer 2 connectivity being possible depending on provider configurations, the official Microsoft documentation and the consensus from highly upvoted comments (including references to specific Microsoft Learn pages) confirm that ExpressRoute's primary operation is at Layer 3. The community discussion shows strong support for Layer 3 with 99% of users selecting this option, and multiple comments reference Microsoft's official documentation that explicitly states ExpressRoute operates at Layer 3.

Author: LeetQuiz Editorial Team