I've been using Ubuntu to roll out different types of network sensors for various reasons.

Frequently relying on promiscous to even perform troubleshooting.

But with the introduction of netplan, apparently, in an effort to be more cloud-friendly or disable this function by default at their request, they seem to have neglected to replace the ifupdown with a package that is comparable.

If you've read this far, I'm also curious to know what distros others have switched to -- that require this function as part of the basic network features enabled by default.

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  • ifupdown does not have native support for promisc mode. If you are looking for the equivalent of ifupdown up or pre-up scripts, you want either udev rules, or networkd-dispatcher hooks. – slangasek Aug 3 '19 at 23:47
  • @slangasek, you are correct, the correct name of the package I was thinking of is actually ifconfig, which I confused in functionality with ifupdown. Will either udev rules or networkd-dispatcher work with netplan to enable promiscuous mode? – taci7 Aug 4 '19 at 17:58
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    I mention both udev rules and networkd-dispatcher because the correct one to use depends on what properties of the device you are intending to modify at which point in the device's initialization. Some device properties can't be changed after a device is in 'up' state, so are better done with udev rules. But the 'promisc' state can be set at any point, so either approach should work. – slangasek Aug 5 '19 at 20:10
  • @slangasek, thank you for this, this is a fantastic way to handle the configuration I was looking to achieve. I hadn't heard about either of these methods previously but researching them, I see many others have had the same frustration/trouble finding a solution: ubuntuforums.org/showthread.php?t=2390958 – taci7 Aug 6 '19 at 21:10

While the move to netplan dropped a commonly used feature that had been long included in the primary mechanism for setting frequently used states on network interfaces. Especially for those that use network taps for applications like snort, bro, suricata, pcap services, etc.; there are lesser-known options that can supplement netplans shortfalls and achieve these desired operations natively in Ubuntu.

This thread, while over a year old, still explains the exact issue, the current state of functionality and workarounds also highlighted in the comments above: https://ubuntuforums.org/showthread.php?t=2390958

Networkd-dispatcher is a set of python scripts that "bridge" the functionality gaps in netplan.

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