What tool should you use to change the address of the default gateway on a Linux server?

The correct tool to change the address of the default gateway on a Linux server is the one that interfaces with network configurations directly at the command line level. In Linux environments, ifconfig is primarily utilized for configuring network interfaces, including setting IP addresses and manipulating routing information.

When you need to change the default gateway, you typically would use ifconfig in conjunction with commands like route or ip (within modern contexts, ip is the recommended command as opposed to ifconfig, which is deprecated in some distributions). However, since the choices provided include ifconfig, it is the tool that signifies the correct approach to managing network settings in Linux.

Other tools like Pinger and Traceroute serve different purposes, such as testing connectivity and measuring the path taken by packets, respectively, without the capability to change configuration settings. The tool IPconfig is specific to Windows environments and does not apply to Linux systems. Therefore, given the context of Linux server management, using ifconfig is the appropriate method for changing the default gateway.