困扰了好久，今天意外看到这篇
不知道有没有版友和我一样买拍卖上面便宜的USB网卡(RD9700)
上Yosemite之后会无法使用，我联系过原厂工程师，给我一个driver还是不能用 ~"~
今天无意间看到这篇，直接转贴上来，已经测试可用
http://blog.inkandfeet.com/How-To-Use-A-Generic-
Usb-20-10100M-Ethernet-Adaptor-Rd9700-On-Mac-Os-1010-Mavericks
Steps to get your adapter working
1. Uninstall the dozens of other drivers you may have installed in the process
of trying to get this working.
2. Unplug your USB adapter, and reboot and give yourself a clean slate.
3. Download and install the drivers from the CD, kindly uploaded by this fine
human being.
4. Reboot.
5. Open your terminal, and run
sudo nvram boot-args="kext-dev-mode=1"
6. Reboot.
7. Open your terminal, and run
"sudo kextload /System/Library/Extensions/USBCDCEthernet.kext"
8. Reboot.
9. Plug in your USB Adapter, with a live ethernet cable.
10. Open System Preferences, and go to the Network Pane.
11. Hit the + button in the bottom right, select the "USB 2.0 10/100M Ethernet Adapter", and hit add.
12. You're all set! Your adapter works!