After upgrading to Yosemite, my Macbook Air drops off the WiFi connection many times a day. The following ping test demonstrates that restarting WiFi leads to a successful reconnection.
$ ping 8.8.8.8
PING 8.8.8.8 (8.8.8.8): 56 data bytes
Request timeout for icmp_seq 0
Request timeout for icmp_seq 1
Request timeout for icmp_seq 2
Request timeout for icmp_seq 3
Request timeout for icmp_seq 4
Request timeout for icmp_seq 5
Request timeout for icmp_seq 6 (Turn Wifi Off, Turn Wifi On)
Request timeout for icmp_seq 7
Request timeout for icmp_seq 8
Request timeout for icmp_seq 9
Request timeout for icmp_seq 10
Request timeout for icmp_seq 11
Request timeout for icmp_seq 12
Request timeout for icmp_seq 13
64 bytes from 8.8.8.8: icmp_seq=14 ttl=49 time=68.005 ms
64 bytes from 8.8.8.8: icmp_seq=15 ttl=49 time=203.014 ms
64 bytes from 8.8.8.8: icmp_seq=16 ttl=49 time=227.464 ms
Why does Yosemite keep dropping Wifi? Mountain Lion was working great. My iPhone is connects to the same Wifi network without a problem.
Best Answer
This isn't a solution, and it isn't a definitive answer, but WiFi/Bluetooth issues have been reported by many users (including yours truly) of OS X Yosemite. Apple is reportedly working on a fix, which may or may not help all of these users.