Both have the ESSID A0B1C2D3E4, so they can join the same wireless LAN; however, the own IP address is 192.168.0.1 on both the current PC and the old PC, which is exactly the same. When IP addresses are duplicated on the same network, it is impossible to tell which device a packet is destined for and the situation is treated as an address conflict, so not only can files not be copied, communication itself cannot work properly.
○イ
正解The correct answer is イ. To copy files between two PCs over a wireless LAN, the two PCs must first join the same wireless network. The name that identifies a wireless LAN network is the ESSID (SSID), and PCs that connect to the same access point (or the same wireless network) must be given the same ESSID. In イ, both the current PC and the old PC have the ESSID A0B1C2D3E4, so they match and can join the same wireless LAN. Next, once they have joined the same network, they must be able to specify each other in order to communicate, which requires that the own IP address set on each PC be within the same network (here, the private IP address space 192.168.0.0/24) and not duplicated. An IP address is a number that uniquely identifies the party you communicate with, so if the same value is set on two machines in the same network, the addresses conflict and normal communication is not possible. In イ the addresses are 192.168.0.2 and 192.168.0.3, which meet the condition that the network part (192.168.0) is common while the host parts (2 and 3) differ. In other words, only イ has the combination of the same ESSID and different IP addresses within the same network, and that is the appropriate setting.
×Incorrectウ
The ESSID is A0B1C2D3E5 on the current PC and A0B1C2D3E6 on the old PC, so they differ and the two machines end up connecting to separate wireless networks, which means they cannot communicate with each other at all. In addition, the own IP address is 192.168.0.1 on both, so it is duplicated as well; neither the ESSID condition nor the IP address condition is satisfied.
×Incorrectエ
The own IP addresses are 192.168.0.2 and 192.168.0.3, so they are not duplicated, and that point is appropriate. However, the ESSIDs are A0B1C2D3E5 and A0B1C2D3E6, which differ, so the two machines cannot join the same wireless LAN. Since they cannot even join the same network, files cannot be copied no matter how correctly the IP addresses are assigned.
ここがポイント
The ESSID (SSID) is the name that identifies a wireless LAN network, and devices that communicate on the same wireless network must be given the same ESSID. If the ESSIDs differ, they are treated as separate networks and cannot communicate with each other.
An IP address is a number that uniquely identifies a device on a network, so it must not be duplicated within the same network. Devices in a LAN share a common network part (192.168.0 in this example) and take different values for the host part. 192.168.x.x is a private IP address range that an organization can use freely within itself.