notified of ip address change

taltman · 07-25-2007, 12:24 PM

Is there a good way in c on linux to be notified(signal/libevent/etc) when the ip address of a network adapter changes? Or is polling the best option?

Things that work in kernel space are fine too this isn't just a user space question.

Mara · 07-25-2007, 03:25 PM

You should connect to the kernel notification chain for addresses. It available on the kernel level, but you can do it in user space (routing daemons do the same).

Take a look into the subcommands of ip monitor. You can either run it and parse the output to find the events interesting for you or write a piece of netlink code (probably looking into ip's source) do do it entirely in your own program.

Edit. To make it clear: the command is

Code:

ip monitor

taltman · 07-26-2007, 02:10 PM

Thanks very much. I found an excerpt of Linux Network Internals on google books that explains notification chains quite well. ip_MASQUERADE.c had just the example I needed.

Tinkster · 07-26-2007, 07:28 PM

Quote:

Originally Posted by taltman

Thanks very much. I found an excerpt of Linux Network Internals on google books that explains notification chains quite well. ip_MASQUERADE.c had just the example I needed.

Sounds interesting ... can you post the link you found
for posteriority? :}

Cheers,
Tink

taltman · 07-26-2007, 07:59 PM

If the link doesn't work just search books.google.com for "linux network internals" and the chain stuff is on page 75.
linux network internals

The chain registration is on line 213.
Just take a look at the struct that is passed to the registration function to find the callback and such.
ipt_MASQUERADE.c

There is a list of the netdevice events starting on line 160.
notifier.h

haxpor · 07-28-2007, 02:33 AM

Thanks taltman, this also led me to another source, "Understanding The Linux Kernel".

http://www.sti.uniurb.it/acquaviva/ulk.pdf

haxpor · 07-28-2007, 02:34 AM

Thanks taltman, this also led me to another source, "Understanding The Linux Kernel".

http://www.sti.uniurb.it/acquaviva/ulk.pdf

haxpor · 07-28-2007, 02:36 AM

Thanks taltman, this also led me to another source, "Understanding The Linux Kernel".

http://www.sti.uniurb.it/acquaviva/ulk.pdf