When troubleshooting a loss of communication to a SQL back-end database, which approach begins by checking physical network connections?

The bottom-up approach is a troubleshooting method that starts with the physical layer of the network. When communication is lost with a SQL back-end database, it's logical to first check the physical network connections, such as cables, switches, and network interface cards. This foundational step is essential as issues at the physical layer can lead to connectivity problems, making it necessary to ensure that all hardware components are functioning properly before looking into the software or configuration layers.

By beginning with the physical layer, you can quickly rule out or identify common issues like disconnected cables or faulty hardware, which can be easily resolved. This method is particularly effective in environments where hardware-related problems are common and helps establish a baseline of functionality on which further troubleshooting can be built.

Other troubleshooting approaches, like top-down, start with the application level and work downwards, which might overlook straightforward physical issues that can be quickly fixed. Divide-and-conquer focuses on isolating the problem through a process of elimination, which may not be the most efficient starting point when physical connections are in question. Evaluation could involve assessing the overall system performance but does not specifically target the tangible attributes of network connectivity. Hence, the bottom-up approach is best suited for the initial investigation in this scenario.