I need to ifdown ifup for real

Question

I am trying to simulate disconnecting the network cable from a pi.

So how do I invoke this? I've tried ifdown / ifup in various different forms.

When I say simulate, you may ask yourself on what level. All, the system must behave as though there has been a break at layer 1 OSI(physical).

Now maybe I sound a bit too stringent in my question, I don't want to go touching drivers and anything on the kernel level.

What I have so far is this, and my ultimate question is: I have a console cable to my cisco router. It has a switch EHWIC card, to which my pi is connected, to one of the ports.

From pi in terminal:

sudo ifconfig eth0 down
sudo ifconfig eth0 up

And the router reports the interface goes down on layer 3 and layer 2. and then up again. Is this the closest I am going to get?

Answer 1

Is this the closest I am going to get?

Going about it this way, yes. The up/down state of a network interface may change as the consequence of a layer 1 event, but it obviously isn't in itself. It's a data link/network layer concern.

I would look into powering off the ethernet controller, which is also the USB controller:

Disable LAN9512

Glancing through /sys on a B+ running a current kernel (4.9.30+) it looks like this stuff has changed a bit; look in /sys/devices/platform/soc/20980000.usb; buspower and bussuspend are writable. The problem then is how to input to the Pi with the USB and ethernet turned off.

Answer 2

I seriously doubt there is a way to simulate a physical break using software only. You will probably have to resort to disconnecting the physical cable or installing smell kind of physical switch in the cable.