Is there an MacOS command that makes a dhcp request, and renews the old lease, drops it for a new one, or usefully reports errors or lack of response from a dhcp server?

This would both help fix networking on the machine after problems on the network without rebooting and would also be useful to diagnose wider networking problems from a mac.

I can not find any command equivalent of dhclient though obviously some component must be serving this purpose. The question is, is that component exposed to a command line interface?

I am biased to the command line for these features and may have overlooked settings panels or tools that might solve it using a gui interface.

I believe this question is at the heart of this other question: Is there an equivalent command for 'init.d/networking restart' in OS X