I have a late 2013 Macbook Pro Retina, with the current update of Yosemite, and I have an odd problem. To be honest, I'm not sure if it's laptop related, or somehow related to my router.
The issue is, when I am connected to my wireless network via 802.11ac, I can't see a shared drive that is connected to my router via ethernet. However, when connected via 802.11n, I can see it just fine.
For the sake of clarity, when I say "see my shared drive", I mean when I open Finder, I see the shared drive listed in the left hand menu under "Shared", I can navigate it's file system, etc.
My router is an Asus RT-AC68U, and the shared drive is a Bubba B3 (basically, a Debian based media server). This is frustrating, as I have to shut off 5 GHz on my router to do backups via Time Machine. Regardless of what protocol my MBP is using to connect, the laptop and the shared drive are on the same network, and in the same subnet. I can connect to the B3 via ssh, and I suppose I could just do a tar based, command line backup of my MBP and scp it over to the B3, but I'd really rather use Time Machine, as it does what it's supposed to do quite well.