What will make carrier changed or lost on Linux?

Question

On my Gentoo, I always got an message said 'carrier changed' or 'carrier lost', what led to a connection lost of interface.

Some of error log:

Jul 10 15:11:18 OpenStackDev kernel: [ 2022.506895] e1000e: enp0s25 NIC Link is Up 1000 Mbps Full Duplex, Flow Control: None
Jul 10 15:11:18 OpenStackDev dhcpcd[3873]: enp0s25: carrier acquired
Jul 10 15:11:18 OpenStackDev dhcpcd[3873]: enp0s25: sending IPv6 Router Solicitation
Jul 10 15:11:18 OpenStackDev dhcpcd[3873]: enp0s25: rebinding lease of 9.111.244.173
Jul 10 15:11:22 OpenStackDev dhcpcd[3873]: enp0s25: sending IPv6 Router Solicitation
Jul 10 15:11:23 OpenStackDev dhcpcd[3873]: enp0s25: broadcasting for a lease
Jul 10 15:11:26 OpenStackDev dhcpcd[3873]: enp0s25: sending IPv6 Router Solicitation
Jul 10 15:11:30 OpenStackDev dhcpcd[3873]: enp0s25: sending IPv6 Router Solicitation
Jul 10 15:11:30 OpenStackDev dhcpcd[3873]: enp0s25: no IPv6 Routers available
Jul 10 15:11:35 OpenStackDev dhcpcd[3873]: enp0s25: offered 9.111.244.173 from 9.0.148.29
Jul 10 15:11:35 OpenStackDev dhcpcd[3873]: enp0s25: acknowledged 9.111.244.173 from 9.0.148.29
Jul 10 15:11:35 OpenStackDev dhcpcd[3873]: enp0s25: checking for 9.111.244.173
Jul 10 15:11:40 OpenStackDev dhcpcd[3873]: enp0s25: leased 9.111.244.173 for 43200 seconds
Jul 10 15:12:14 OpenStackDev dhcpcd[3873]: enp0s25: carrier lost
Jul 10 15:12:14 OpenStackDev kernel: [ 2079.050129] e1000e: enp0s25 NIC Link is Down

And this only happens when I open a VM, what I use is VirtualBox 4.2.14 I wanna know what makes carrier changed or lost, and what does this carrier mean?

Answer 1

In real physical machines a carrier would be your network cable

If you are connected using network cable and you unplug it you should see similar message.

In virtual machine I am not sure what causes it, maybe you changed your network type or disconnected it in the virtual machine while its running?