If you need to do a lot of network testing, the Raspberry Pi is a cheap way to do it. NetPi is a custom operating system that includes all the tools you'll need.
NetPi comes packed with CDP/LLDP, DIA diagram software, ping/trace/speed test tools, pen testing tools and more. Obviously, it's not a use case most of us need all the time, but it's handy to keep an SD card around with NetPi installed for when you need it. You can can find the guide for setting this up for yourself over on Blame the Network.
NetPi Build Guide [Blame the Network]