(A user is unable to access a web application.

Routing issues are investigated at the Network Layer (Layer 3) of the OSI model. AI+ Network foundational documentation explains that the Network Layer is responsible for logical addressing and packet routing between networks using IP addresses.

If a user cannot access a web application due to routing problems, issues may include missing routes, incorrect gateway configuration, routing loops, or unreachable networks. Troubleshooting typically involves examining routing tables, gateway settings, and path selection mechanisms at Layer 3.

The Data Link Layer handles local frame delivery, the Transport Layer manages end-to-end communication using TCP or UDP, and the Application Layer relates to services such as HTTP. AI+ Network materials consistently reinforce that routing failures are diagnosed at the Network Layer.