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When using the terminal tool ip, there is a number of flags for every interface.

Example: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP,M-DOWN> mtu 1500 qdisc noqueue

What is the meaning of M-DOWN? What command to be used to make it up or down?

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    Are you sure this is for `eth0`, and not for something like `eth0:0`? I've only seen this in slave devices, and I'd always assumed it means "m(aster device) down". – dirkt Mar 01 '17 at 09:57
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    It appears M-DOWN is similar but not equivalent to LOWERLAYERDOWN and is retrieved by checking the peerlink state. This failed in the past at least when the peerlink was in an other namespace, and still fails for this reason today in busybox's minimal implementation. An answer would be complex because having to pinpoint exactly the role of M-DOWN vs LOWERLAYERDOWN (which I'm avoiding here because it's still not clear) and also address the failures of different versions of different tools when network namespaces are in the equation. Can easily be seen with *veth* interfaces and alpine container – A.B Nov 29 '20 at 14:15

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