Using a systemd.service file to control promiscuous mode automatically at boot

At some point while working on a Salt formula to deploy pfring, I got to a point where I wanted to set promiscuous mode on an interface automatically. I wasn’t exactly sure how to go about it on RHEL/CentOS 7. So many things have changed so I set out to do a quick google search. I found my Google foo was not very strong and searched for several solutions. As you might expect, I wasn’t able to find a suitable solution very easily. I eventually came across an article on an arch Linux forum that lead me to my solution. I thought I would write a quick blog post so I don’t forget as there is one addition I made, which allows the service to be stopped as well.

On RedHat or CentOS 7 create a new service file at /usr/lib/systemd/system/netcfg@.service

Add in the following contents:

Description=Control promiscuous mode for interface %i

ExecStart=/sbin/ip link set %i promisc on
ExecStop=/sbin/ip link set %i promisc off 


When you start or stop the service, pass in the name of the interface you want to enable/disable promiscuous mode on.

Turn on: systemctl start netcfg@eth1
Turn off: systemctl stop netcfg@eth1

Automatically enable at boot.

systemctl enable netcfg@eth1


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