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What is creating the utun0 network interface on OSX? What is it being used for? What is it exactly?

The interface only appears after connecting to the Ethernet or turning on the Wi-Fi and goes away after restart. It does not show up in the Network Preference Pane. Using ifconfig the interface looks like this.

utun0: flags=8051< UP,POINTOPOINT,RUNNING,MULTICAST> mtu 1380
inet6 fe80::c502:a4a6:a260:e0d1%utun0 prefixlen 64 scopeid 0x7
inet6 fd4c:2989:56f0:25be:c502:a4a6:a260:e0d1 prefixlen 64
nd6 options=1<PERFORMNUD>

My next question would be why the MTU size of 1380, but maybe it would help if i understood what this interface is, what is it being used for, and what is responsible for it's creation.

I'm NOT using a VPN. I do have Wireshark installed and GNS3 and VirtualBox. I don't know if any of those applications would be responsible for the creation of utun0. I'm interested in man pages, documentation, or guides from which I can learn more. Any help or suggestions appreciates.

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  • I see that inet6 beginning with FE80 is an IPV6 link-local address. I should also mention the interface dose not appear to be associated with any service, though other than the command: networksetup -listallnetworkservices May 14, 2015 at 14:14

1 Answer 1

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utun0 is For "Back to My Mac" given your described setup I would assume it's created by GNS3 for / as the secure localhost connection.. as for the MTU not sure

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  • Thank you! On another test machine running OSX 10.8, I experimented by enabling and disabling Back To My Mac and the utun interface would appear and disappear as expected. For some reason the same doesn't hold true on my 10.9 machine. The utun interface remains even when Back To My Mac is disabled. May 14, 2015 at 20:23
  • try reverting to mDNS (the default pre - yosemite) (searching 'Yosemite DNS broken ' will furnish plenty of tutorials for that is that works its the new largely broken discoveryd May 15, 2015 at 0:08
  • I am running pre-Yosemite. I'm on Mavericks. The utun0 interface is not causing any issues which I can see. I just wonder why it gets automatically created. If I could remove it manually, perhaps with a networkseup command, then I could troubleshoot it better. May 16, 2015 at 4:59
  • There is no discoveryd process running that I can find. I'm running Mavericks which still uses mDNSResponder. May 18, 2015 at 7:18

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