Programmatically enable / disable the UNIX network interface

Question

There are many very similar questions, but they are all for Windows - I want to know how (if possible), I can make my C program (run as root, on Linux) disable the network interface so that it no longer receives any packets.

If someone tells me what functions I need to do, it will be great, but even better if you can link me to an example script or tutorial somewhere that (example) gratia disables the network interface again.

Answer 1

For Linux, everything is easily doable with MNL and knowledge of the RTNL protocol:

http://git.netfilter.org/cgi-bin/gitweb.cgi?p=libmnl.git;a=blob;f=examples/rtnl/rtnl-link-set.c;hb=HEAD

In Unices or other operating systems, only an OS-specific call and / or an archaic ioctl call are available, the last of which cannot correctly express multiple Linux addresses on one interface, so serious programs do not use it on this platform.

Answer 2

You do not have a complete example, but you should start the following keywords (at least on Linux, not sure about other versions of Unix):

ioctl, SIOCSIFFLAGS, IFF_UP

The following may be useful for showing you the appropriate APIs: http://www.google.com/codesearch/p?hl=en#2--Ws53NXRc/src/ifdown.c

Answer 3

On Linux, you can use ifdown . I do not know how this is carried over with other unixes.

Answer 4

On Linux and most of the Unix-based systems I used, ifconfig <interface> up/down used to move the interface up or down. Not sure if there is a C procedure for this without running ifconfig.

Answer 5

On Linux, the ip link set down dev ethX does nothing more or less what you want. I would suggest calling this program to do your job if you are on this platform.

If you want to do it yourself, the C api is not an easy thing to do. You can dive into the iproute source to find out what it does.

Check out @ user611775's answer for a great example of how to do this in C.

If you are on a different Unix, the answer will probably be different for each particular taste.