Strange Computer name occurance

[zmbarker]

Does anyone else experience a strange behavior with the computer names on some of the clients?

Each computer is named after the asset tag that we put on the computer. Ex: D20141020
ComputerName = D20141020
HostName = D20141020
LocalHostName = D20141020

The JSS has this information correct. Then at some point for an unknown reason the ComputerName might change to D20141020 (2319) or D20141020 (4) or D20141020 (11).

Out of our 500 computers in the JSS this might occur on 5-10 computers.

Before you ask...
no - the computer names were never changed on purpose, this is a random quark.
yes - sometimes the HostName or LocalHostName is changed, most of the times it is the computername only.
no - this occurs on computers that were either imaged by Casper or they were just "enrolled" by going to https://myJSSurl.com/enroll

yes - I can just rename the device on the JSS and force a "Reset ComputerName" and all is fine again.

Just curious if others in the community experience this issue.

[justinrummel]

Do the machines that change their name by chance share an external dongle? Thunderbolt to Ethernet? I thought JSS v9 removed the MAC address association to a unique GUID so this would be odd if you were on the latest version.

[calum_carey]

looks like bonjour is renaming them. Do you have a bonjour gateway on the network? Aerohive AP or avahi repeater?

[zmbarker]

@justinrummel - I thought about the thunderbolt dongle thing to, but this even occurs on computers that have never had "my tech assigned" dongles on the machines.

@calum_carey - I am not sure if we have an Avahi repeater or Aerohive AP on the network. How would bonjour be renaming the computernames? Is that what bonjour normally renames computer names by putting a (##) behind the computername? Do you have any suggestions on how I can resolve this?

I am curious on why @calum_carey thinks bonjour is making the change.

[calum_carey]

bonjour/mDNS you can't have two machines on the same subnet with the same name. this causes a name conflict. so bonjour/mDNS to append a number in brackets to the computer name of one of the machines in order to resolve the naming conflict.

If you have an avahi repeater or aerohive ap on the network i have seen instances where the computer name is cached so even though there isn't two machines on the network with the same name, bonjour/mDNS thinks there is so it sends the message to the machine to append a number to its computer name.

as a test grab two machines put them on a unmanage switch connected to nothing else. let the machines get their own link local 169.254.x.x ip addresses. now give them both the same name and watch what happens.

[JPDyson]

That's the hunch I had; I've seen this before but haven't been able to eliminate it. The Mac is being told that the name it has already exists on the network, so it's appending a suffix.

[zmbarker]

I guess I can understand that behavior, but why is it not just giving the number (2)/(3)/(4)/(5) and giving numbers like (658)/(4)/(2375)?

[calum_carey]

ahh welcome to the wonderful world of mDNS ;)

[zmbarker]

how do I fix this on any of the current machines?
How do I make sure this doesn't happen anymore? Do I need to disable something on each of the machines?

[acdesigntech]

You'll need to ensure the machine name is whatever you originally set it as with a jamf setComputerName, then re-recon it. Should update the name in Casper immediately.

I have not found a way to prevent this issue, only mitigate it via a LaunchDaemon on laptops to enable/disable wireless when an ethernet cable is unplugged or plugged in, and to disable wireless on all desktop models via MCX so users cannot turn it back on.

The issue STILL happens to me every once in a while when DNS scavenging lags ever so slightly behind a DHCP lease renewal :(