I am trying to detect the number and type of interfaces installed on a host and their IP addresses using the ioctl function. It returns the type of interfaces and their IPv4 addresses but is unable to return the the correct IPv6 addresses. Richard Stevens suggested in his book that IPv6 implementations do not return IP addresses with ioctl function.

I shall be grateful for any suggestion of an alternative.

OMAR

Well according to the netdevice(7) man page the ipv6 addresses can be retrieved either from /proc/net or through rtnetlink.

You might want to read the rtnelink 3 and 7 man pages.

Hello Mik

I tried man rtnetlink(7) and it talks about message formats. man rtnetlink(3) shows an incomplete example but in the end the man page suggests that the page is incomplete and incorrect.

If I understand it correctly, I need to form an appropriate message and send it over the socket opened for PF_NETLINK family. The reply I will receive will contain the required IP addresses.

OMAR.

Well I've never worked with ipv6 addresses nor with the netlink interface. I found some source code which describes how to use the netlink interface to get ip addresses, it is however for ipv4 addresses but it should work with ipv6 with a few modifications. Basically changing the family to AF_INET6 and changing the way the addresses are displayed should be enough. Anyways the example program is here:

http://linux-kernel.skylab.org/20010902/msg00920.html

The example program does however require you to be root to bind to the socket. But to get netlink information it's not necessary to bind to a socket. So just remove the bind part and you can run it as a normal user. Hope that helps somehow.

I was struggle with this for quite a while. And my best solution for this is open the file in /proc/net/if_inet6 and read out from there. That is how the net-tools did. It is the cheapest and easier way for getting the information that you want. You just need to play around with the file reading format. That is the tricky part.