I get that sometime too. Sometimes it's my router and sometimes it's my modem. Router and modem have operating system in order to do their jobs. Some Linksys router runs a version of Linux that you can get a hack for. Therefore, the problem is probably caused by an unrecoverable error, similar to a kernel panic or a blue screen of death. Another thing that I'm thinking is that the router could be detecting a hacking attempt and shut itself down in order to save the network.