I thought it only worked over Wi-Fi? Doesn't it rely on Airport?

From http://support.apple.com/kb/ht4783:

"Make sure Wi-Fi is turned on at both computers. Although you don't have to connect to a specific network, Wi-Fi needs to be turned on to transmit and receive files wirelessly."

Oh I suppose there's this: http://www.cultofmac.com/201554/enable-and-use-airdrop-via-ethernet-on-older-macs-os-x-tips/

Maybe you can try running that command on a Mac that isn't functioning as you expect to see if it helps…

It was able to be modified previously (10.7-10.8)to also use ethernet via the command line with either ```
defaults write com.apple.NetworkBrowser BrowseAllInterfaces 1

Or

defaults write com.apple.NetworkBrowser BrowseAllInterfaces -bool true
```
This doesn't seem to work however on the same machines in 10.9 from what I'm finding.

Gabe Shackney
Princeton Public Schools

Found this, but I don't know why anyone would want to.

http://osxdaily.com/2011/09/16/enable-airdrop-ethernet-and-unsupported-macs/