MacBook – Local hostname is already in use on this network

dnshostsmacbook proNetworkwifi

When I turned my computer on this morning this is the message I received:

This computer's local hostname "----Macbook-pro.local" is already in
use on this network. The name has been changed to
"------Macbook-Pro-2.local" To change the local hostname, open system
preferences and click sharing, then click "edit" and type the name in
the local hostname field.

This is very concerning to me since I can't think of any reason this should happen. I do not understand any of the answers I have read while do a search. I have not done anything complicated nor do I have a WiFi along with an Ethernet connection – only a WiFi connection.

I only have one router as well and I always connect to same network. The things I have done differently are:

  • I have added a printer and have also downloaded Whatsapp but have not used it yet.
  • I opened Skype last night and have not done that in a while so maybe that could be the reason?

This is very concerning to me since I can't think of any reason this should happen unless it has something to do with what I said above. I am not comfortable changing settings that I really do not understand. I also felt as if I have been hacked or whatever it is called when someone takes over your computer. As I said, I am not an expert by any means and this is worrisome to me.

Can anyone please help and explain it in a way that I might understand what has happened. Thanks! Kind regards!!

Best Answer

To analyze what might be this ghost network host, the command to use is a command line (which you have to run in Terminal or xterm):

dns-sd -G v4 ----Macbook-pro.local

If this name really exists within your accessible Wi-Fi network, then you will get its IP address within the last column of output of this command as in this example:

DATE: ---Sat 09 Dec 2017---
 0:42:42.548  ...STARTING...
Timestamp     A/R Flags if Hostname                               Address                                      TTL
 0:42:42.856  Add     2  6 ----Macbook-pro.local                  10.0.2.23                                    120

If you just get one IP address, then this error message was probably an internal bug within the MacOS way to manage its DNS cache.

If you get two different IP addresses, then you have an uninvited host within your network and behind your firewall (i.e. directly on the Wi-Fi part). This might be one of your neighbor. To continue on its correct identification, you will have to use methods which are considered as direct attacks on someone's computer.

For example, you might use iStumbler to physically locate it and then have a chance to interview the owner of this new visitor of your network.

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