The power down, power up sequence has been a standard fix for network problems since the advent of WiFi. It is seldom used these days because improvements in the firmware and software of all the devices involved have made the network connectivity much more stable so it is seldom needed and therefore often overlooked as a solution.
It is likely nothing went astray with your 10.10.4 install other than during the installation and reboot process you lost synchronization somewhere between you computer and the other network devices. The reset sequence allowed each device to re-establish its connections. To comprehend how something like this can happen, you need to have at least a passing understanding of the OSI 7 layer communications model.
Stepping back into my previous life as a technical trainer and college lecturer: For the most part it is convenient to view an network or internet connection as single entity, like a string tied between two tin cans, but it is far more complicated than that. The
Wikipedia article on the OSI model succinctly describes each of the layers so I won't attempt to go into that here. Suffice it to say that each layer provides for reliability and integrity of communications FOR THAT LAYER but each layer is dependent on the services provided by the preceding layers working as advertised. While the TCP/IP protocol of the internet does not deal with each OSI layer discreetly, all seven functionalities are still there. Each layer in each device has to "shake hands" with the corresponding layer in every other device in the communications chain. So it is entirely possible for there to be successful
hand shaking at say the physical and data link layers — which will appear as a successful network connection — , but a disconnect in the Network layer which would block connections in the subsequent layers. The sequential device restart
fix allows each device to establish a solid connection and
hand shaking between the layers it is responsible for. The computer is last because it has responsibilities in all seven layers.
By design all of this is on a device by device basis so it is entirely possible for one computer to have a communications disconnect while other computers in the network continue to communicate normally.
