No, this is a symptom of a DNS error. or bug problem that that comes and goes, usually in Yosemite, but it can occur in Mavericks as well.
There is no real "fix" until the software is improved. Devices may appear using their name, their IP address, or their MAC Address.
Try power cycling the entire network to see if that allow the operating system to remember network devices correctly. To do that.....
Power off all devices on the network....in any order that you wish.
Wait a minute
Power up the modem, and let it run for 2-3 minutes
Then, power up the next device connected to the modem, which might be your Extreme
Keep powering up devices one at a time about a minute apart until the entire network is back up
Check the network
It might help, or it might not. Or,if it helps, it may not be for long.