Assume a future where security countermeasures against DoS attacks are much more widely implemented than at present. In this future network, antispoofing and directed broadcast filters are widely deployed. Also, the security of PCs and workstations is much greater, making the creation of botnets difficult. Do the administrators of server systems still have to be concerned about, and take further countermeasures against DoS attacks, if so, what types of attacks can still occur, and what measures can be taken to reduce their impact?