If you have just gained access to a network, one of the first things you can do is to get an idea of what hosts are on the network. You can scan all IP addresses on a subnet and then do a DNS lookup to see if you can find any named hosts. Hostnames can have descriptive or informative names that give clues as to what a server may be running.
The pure Go resolver is default and can only block a goroutine instead of a system thread, making it a little more efficient. You can explicitly set the DNS resolver with an environment variable:
export GODEBUG=netdns=go # Use pure Go resolver (default)
export GODEBUG=netdns=cgo # Use cgo resolver
This example looks for every possible host on a subnet and tries to resolve a hostname for each IP: