Yun not connecting to Internet through Ethernet wired connection: Please observe

Can you please explain this part? What is the "metric" parameter, how do I set it, and why does it affect IDE connection?

I have no wifi on the old desktop PC I'm using; connecting over ethernet allows me to see SD card contents (so I know connection is working), but Yun IP address does not appear in IDE menu, so I can't upload sketches and web pages.