```
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN mode DEFAULT group default 
link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00

```

The `UP` between the brackets means my link is operationnally up. But what does the `state UNKNOWN` mean ?

I went through this [doc](http://www.policyrouting.org/iproute2.doc.html#ss9.1.2) but could not find anything related to it.