In addition to Mike's excellent answer, I wanted to add my thoughts.
I think it would be a mistake for ServerFault to remove networking questions from their on topic subjects. While there are many network questions asked there that would fit here, there are quite a number of them that won't.
ServerFault is targeted more at systems administrators. In many cases (small businesses, non-profits, etc) there may not be a dedicated network professional, and the system administrator(s) are also expected to run/maintain the network.
Consider the fact that there exist a number of businesses that run with consumer grade network equipment but do have a systems administrator on staff. This type of environment would be off topic here because of the equipment, but on topic at ServerFault.
Or even if the small business was using equipment that would be on topic, the systems administrator may not be able to ask a question that would meet our quality expectations here, but might work on ServerFault.
While this does create overlap in some areas, this is by no means a bad thing. In my mind, it is better to have overlap so that people are able to find answers to their questions than to enforce a separation that may allow for a situation where some questions just aren't on topic anywhere.