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ifup and ifdown
Apr 2020
Overview
If have been using ifup and ifdown for quite some time now, and as far as i was aware the syntax was pretty simple, however I got really caught out the other day and wanted to share what I discovered (not entirely on my own, with the help of some other, way more clever people).
Simple Syntax
So, to take down an interface, I would use the following:
ifdown eth1
Device 'eth1' successfully disconnected.
Simple, and to bring that interface back up:
ifup eth1
Connection successfully activated (D-Bus active path: /org/freedesktop/NetworkManager/ActiveConnection/3)
Wow, too easy. I use this normally when I have changed and IP Address and want to invoke that change quickly (without using the systemctl command or a reboot).
What Went Wrong?
Now, this is not going to affect everyone, but in our systems we sometimes have to prove redundancy by taking down an interface, letting a device detect this and watching the system automatically switch. Sounds simple enough, but it seems that using a simple ifdown or ifup does not cause a redundancy switch, you need to do a bit more.