問58
頻出度★★★
PC1をインターネットに接続するための設定を行いたい。PC1のネットワーク設定項目の一つである“デフォルトゲートウェイ”に設定するIPアドレスは，どの機器のものか。 〔ネットワーク構成〕 ・LAN1：PC1，PC2，ルータ，DHCPサーバが接続されている。 ・LAN2：ファイアウォール，プロキシサーバが接続されている。 ・ルータはLAN1とLAN2の両方に接続している。 ・ファイアウォールはLAN2とインターネットに接続している。
平成31年度 春期 ITパスポート試験 問58
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 58
- ア
正解 In the default gateway you set the IP address of a device that is on the same network (subnet) as yourself and that relays packets to external networks. PC1 is connected to LAN1, and as shown in the figure the device that relays packets across LAN1 and LAN2 is the router. Therefore, when PC1 communicates with the Internet (outside LAN1), it must first hand its packets to the router on the same LAN1, so the router's IP address is set as the default gateway. Hence the correct answer is ア.
Incorrectイ
The firewall is indeed the entry/exit point to the Internet, but it is connected on the LAN2 side and is not directly connected to the same network (LAN1) as PC1. Only a device on the same subnet can be specified as the default gateway, and the nearest relay point seen from PC1 is the router, so this is wrong.
Incorrectウ
The DHCP server is a device whose role is to automatically assign IP addresses, gateway information, and so on to each device; it does not have the routing function to relay packets to other networks. It cannot itself act as a gateway, so this is wrong.
Incorrectエ
The proxy server is a device that acts as a proxy for application-level communication such as the Web; it is on the LAN2 side and is not on the same network as PC1. In addition, the proxy is a setting configured on the application side, such as in the browser, and does not correspond to the default gateway, so this is wrong.
ここがポイント
- In the default gateway, set the IP address of the router that is on the same subnet as yourself and that relays packets to external networks.
- A device on a network different from PC1 (on the LAN2 or Internet side) cannot be specified as the default gateway, because it cannot communicate directly.
用語