At which OSI layer does ExpressRoute operate?
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A. B. C. D.A
ExpressRoute circuit. A layer 2 or layer 3 circuit supplied by the connectivity provider that joins the on-premises network with Azure through the edge routers. The circuit uses the hardware infrastructure managed by the connectivity provider.
In OSI terms, you start from layer 2 The Network Service Provider concept was a managed concept, where you got a layer 3 solution (in OSI terms). The telecom provider took care of all the complexity for you.
https://docs.microsoft.com/en-us/azure/architecture/reference-architectures/hybrid-networking/expressrouteExpressRoute is a Microsoft Azure service that allows organizations to create private connections between their on-premises infrastructure and Azure datacenters. It provides a dedicated, private network connection over a telecommunications provider's network or through a co-location provider.
Regarding the OSI (Open Systems Interconnection) model, which defines how data is transmitted between different networked devices, ExpressRoute operates at Layer 2 and Layer 3.
Layer 2 (Data Link Layer) is responsible for the transfer of data between adjacent network nodes in a wide area network or between nodes on the same local area network (LAN). ExpressRoute uses Layer 2 to establish a dedicated, private connection between the customer's on-premises network and Azure.
Layer 3 (Network Layer) is responsible for packet forwarding between different networks. ExpressRoute uses Layer 3 to connect the customer's on-premises network to Azure virtual networks using a dedicated IP address space.
Therefore, the correct answer to the question "At which OSI layer does ExpressRoute operate?" is A. Layer 2 and B. Layer 3. ExpressRoute operates at both layers to provide secure and reliable connectivity between on-premises infrastructure and Azure.
Option C, Layer 5 (Session Layer), and Option D, Layer 7 (Application Layer), are not relevant to ExpressRoute as they deal with the management of sessions between applications and the actual applications themselves, respectively.