macOS keeps changing computer name

Not quite sure what you are saying as there isn't any MAC address (otherwise known as an ethernet address) associated with the loopback interface since it's just on the machine and not the network - perhaps what you call "mac" is something different? Maybe you could explain (or better post the output of your "netstat -rn" command - change so that no personal info revealed, but don't change so much that you change what is related to what - does that make sense?).

Do you have multiple "lo" type interfaces, e.g. lo0, lo1, etc? Not sure if this is possible under normal circumstances.

You could always remove a redundant interface using appropriate "ifconfig" command in Terminal (do a "man ifconfig" to see details).

Another thing that has helped me in the past is to simply "Make Service Inactive" and wait a bit, then "Make Service Active" for the the appropriate network interface in the System Preferences Network pane. Select the appropriate interface first before clicking the options button.The "Make Service Inactive" option is shown when you click on the options button at the lower left part of the pane:

Good luck...

I would check them all just in case. I have the same problem when I am cloning from my iMac to my MacBook and forget to change the computer name. It's pretty common problem in home networks with multiple computers on the local network.

You will get that error message when you have two machines competing for the same IP address on the same LAN segment. Watch out for overlapping DHCP address ranges on different Macs, or statically assigned IP addresses that fall inside those same address ranges.

Usual reason I've encountered for that arising on current versions of macOS is a loop somewhere in the local network topology; where the problematic system can "see" itself via additional network paths. That's usually an incorrectly-configured network such as some wired and Wi-Fi connections, or multiple local network connections.

What's the local network configuration look like? Routers, switches, Wi-Fi devices, wired connections, etc. If there's both wired and wireless, then that usually either needs to be reconfigured into separate IP subnets with an intervening router, or the Wi-Fi device(s) should be switched to its access point mode (if the Wi-Fi device supports that).

I've also occasionally seen this misbehavior with the Bonjour sleep proxies in years past, but whatever was wrong with that was seemingly fixed in some of the now-older Airport and Time Capsule firmware updates.

Typically either the Wi-Fi has to be configured as an access point (which effectively makes it "transparent" to IP routing and effectively part of the wired network), or the Wi-Fi and the wired networks should be configured into separate subnets. Having the same IP subnet on either side of a router doesn't tend to work all that well.

Same general issue applies to VPNs too, where having the same IP subnet on each end of the VPN tends to cause IP routing to work less than reliably.

Or disable either Wi-Fi or wired routing on the box; one network connection per box.

I usually configure Wi-Fi as an access point anyway, as that means roaming around a network with more than one Wi-Fi box works far better.

An access point is closer to an Ethernet cable in terms of its role in a network. Routers look much deeper into thr network traffic. Access points do not involve IP subnets or IP routing or NAT or other other network-related tasks.

Do you have an access point, or a Wi-Fi router? If you didn’t purchase an access point or didn’t explicitly reconfigure a Wi-Fi router, the device is almost certainly a Wi-Fi router.

Does your Mac have more than one network connection configured, connected, and active? Both Wi-Fi and wired connections active and connected, for instance.

If there are not multiple network paths in the local network within the device providing either firewall/gateway/NAT (common config, often using a Wi-Fi device fulfilling multiple roles) or (less commonly) routing and firewall services for your network, do you have a network device that supports the Bonjour sleep proxy? That’s most commonly either an AirPort or a Time Capsule, but there are probably a few other devices that offer the sleep proxy feature.

You need to precede the "set" option with two dashes, not one...

sudo scutil --set computername "xxx"

Do a "man scutil" in a Terminal window if you want to see more details about "scutil" command.

Also, you can try to see what the network looks like by using the "netstat -rn" (to see an IP address list) or "netstat -r" (to see a hostname list) Terminal command. You will see a list of all the known network devices and interfaces - you might even learn what might be conflicting with your existing computer. If you do use the "netstat -r" command, it might take a while to resolve all IP addresses to their actual hostname, so be patient (the "netstat -rn" always will return much faster since no hostname lookups are involved, which can take a while for networks with lots of attached devices).

Good luck...

zappe wrote:

I've now set all the names and will see what happens.

Likely won’t help. That’s the command line interface to the Bonjour settings and to some unrelated settings. Which means you can set that or set the name via the GUI, and get the same result.

I tried netstat -r and got two of my computer name..

That command shows some routing data. It’s not (directly) related to having a Bonjour network host “visible” by more than one network path; a loop.

The network interfaces I have is Wi-Fi, Bluetooth PAN, My phone and Thunderbolt Bridge.

Which of those are active and connected? If there is more than one connected and active, pick the fastest and temporarily shut off the others, and see if the Bonjour problem resolves itself. Or provide a little more description on how the different paths might cross-connect into your local network.

Also, please describe your network configuration in a little more detail? What network-related boxes are connected? Switches, Wi-Fi devices, Access Point devices, gateway/firewall/NAT boxes, and that ilk. (What other clients are connected to the local network usually isn‘t relevant to a network loop.)

ps: I’m referring to a network loop here, and not to the IP loopback device. That’s something diferent.

Is the router box separate from the Wi-Fi box? If so, is the Wi-Fi network either configured in a different subnet, or configured as an access point? Because if the router and the Wi-Fi are separate boxes (and if the Wi-Fi is configured as a router and not an access point), then there are two routers here, and two routers need to have separate subnets.

See this article macOS Sierra: Change your computer’s local hostname

Are there any other computers in the house even those that use Wi-Fi and Ethernet?

Neighbors using your router?