問64
頻出度★★★
無線LANの環境において,アクセスポイントと端末に設定するESSIDに関する記述として,適切なものはどれか。
平成24年度 秋期 ITパスポート試験 問64
テクノロジ系ネットワーク › ネットワーク方式
This question's explanation and your answers so far.
解説
問 64
Incorrectア
The character string that becomes the key for encrypted communication is the WEP key, or the pre-shared key (PSK), that is, the passphrase, used with WPA / WPA2; it is a setting item configured separately from the ESSID. The ESSID is a name for telling connection targets apart, so it is meant to be disclosed to the terminals around it (it is broadcast in beacons), and if it were used as an encryption key it could not remain secret. It helps to recall that wireless LAN connection setup has two stages: you first choose the network name (ESSID), and then enter the encryption key as the password.
Incorrectイ
The type of encryption method refers to the names of encryption schemes such as WEP, WPA, WPA2 and WPA3, and TKIP or AES (CCMP) used within them. These are selected in a field separate from the ESSID on the configuration screen of the access point, and they are security settings about how strong a scheme to choose. The ESSID is merely the name of the network and does not indicate the name of a scheme.
Incorrectウ
The channel number of the radio waves used by a wireless LAN is a number that indicates a frequency division obtained by finely splitting the 2.4 GHz band or the 5 GHz band, and it is a setting item chosen so as not to cause radio interference with nearby access points. It is a numeric value, not a character string, and the terminal side normally scans the radio waves of access points and matches automatically, so it is not something a user types into the terminal by hand. It differs from the ESSID in both purpose and setting content.
- エ
正解 The correct answer is エ, a character string that identifies the wireless LAN network. ESSID (Extended Service Set Identifier) is an identifier that acts as the name given to a wireless LAN network, and it can be set to up to 32 characters using single-byte letters and digits and the like. Because radio waves reach anyone within range, in situations where several access points transmit in the same space, such as an office or an apartment building, a terminal has to use the name to pick which network to connect to. So the ESSID is configured on the access point, and the same ESSID is also configured on the terminal (or selected from the list of detected networks); only then can the terminal join that wireless LAN. Originally an SSID identifies the communication area (BSS) created by a single access point, but if the same ESSID is set on several access points, they can be treated together as one network, and a terminal can switch to an access point with a stronger signal while moving and keep communicating (roaming). An access point normally broadcasts this ESSID periodically as a beacon, and the network name shown in the terminal list of connection targets is exactly the ESSID. Note that the ESSID is only a name for identification and by itself has no function that protects the content of communication. A stealth function that does not broadcast the ESSID, and a setting that rejects connections from terminals whose ESSID is empty (ANY), are only supplementary measures that make the network harder for unrelated terminals to find; to prevent eavesdropping, separate encryption such as WPA2 is required.
ここがポイント
- The ESSID is the identifier of a network: it is a name of up to 32 characters given to a wireless LAN network, and setting the same value on the access point and on the terminal lets the terminal uniquely pick which network to connect to. Setting the same ESSID on several access points lets them be handled as one network, which makes communication while moving (roaming) possible.
- Separate the wireless LAN setting items by role: the ESSID (identifying the network), the encryption method (WEP / WPA / WPA2 and so on), the encryption key (WEP key, pre-shared key / passphrase) and the channel number (the frequency division of the radio waves used) are each a different thing. The ESSID itself has no encryption or authentication function, and the stealth function or rejecting ANY connections remain only supplementary measures, so encryption is essential as a countermeasure against eavesdropping.
用語