what does none in "tun0@none" stand for?

In the output of ip a I just got the lines:

4: tun0@NONE: <POINTOPOINT,MULTICAST,NOARP,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UNKNOWN group default qlen 100

What does the NONE in there stand for?

Asked By: Florian

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According to the output format documentation,

The interface name may have another name or NONE appended after the @ sign. 
This means that this device is bound to some other device,
i.e. packets send [sic] through it are encapsulated
and sent via the “master” device. 
If the name is NONE, the master is unknown.

  [Emphasis added.]

So your tun0 interface is part of a tunnel bound to another networking device. The fact that ip does not know which one does not mean that the tunnel will not work.

Answered By: Emeric
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