Question

I have used the program which is present in the following link http://www.linuxhowtos.org/manpages/3/getifaddrs.htm .

but it prints all the IP like loopback,eth0,eth1 lo etc

now I need to get only the ip which are active excpet loopback ip
ex

$iffconfig
eth6 Link encap:Ethernet HWaddr 08:00:27:47:99:da
inet addr:10.0.2.15 Bcast:10.0.2.255 Mask:255.255.255.0
inet6 addr: fe80::a00:27ff:fe47:99da/64 Scope:Link
as the ifconfig gives the active interface and correspoding IPs

what has to be changed in this code to get the above thing working ?

Answer 1

Change

    if (ifa->ifa_addr == NULL)
        continue;

    family = ifa->ifa_addr->sa_family;

with

    if (ifa->ifa_addr == NULL)
        continue;

    if ((strcmp("lo", ifa->ifa_name) == 0) ||
        !(ifa->ifa_flags & (IFF_RUNNING)))
        continue;

    family = ifa->ifa_addr->sa_family;

and add this line just after the other includes

#include <net/if.h>

The added lines just check for “lo” interface name, contained into ifa->ifa_name, and check the flags of the interfaces. Testing IFF_RUNNING bit ( look at net/if.h for further definitions) will return only running interfaces.

If you want to check other feature of the interfaces, just check for this flags (taken from net/if.h)

• IFF_UP Interface is running.
• IFF_BROADCAST Valid broadcast address set.
• IFF_DEBUG Internal debugging flag.
• IFF_LOOPBACK Interface is a loopback interface.
• IFF_POINTOPOINT Interface is a point-to-point link.
• IFF_RUNNING Resources allocated.
• IFF_NOARP No arp protocol, L2 destination address not set.
• IFF_PROMISC Interface is in promiscuous mode.
• IFF_NOTRAILERS Avoid use of trailers.
• IFF_ALLMULTI Receive all multicast packets.
• IFF_MASTER Master of a load balancing bundle.
• IFF_SLAVE Slave of a load balancing bundle.
• IFF_MULTICAST Supports multicast
• IFF_PORTSEL Is able to select media type via ifmap.
• IFF_AUTOMEDIA Auto media selection active.
• IFF_DYNAMIC The addresses are lost when the interface goes down.
• IFF_LOWER_UP Driver signals L1 up (since Linux 2.6.17)
• IFF_DORMANT Driver signals dormant (since Linux 2.6.17)
• IFF_ECHO Echo sent packets (since Linux 2.6.25)

EDIT

if you need to discriminate IPV6 GUA and ULA address use this macros

#ifndef IN6_IS_ADDR_GLOBAL
#define IN6_IS_ADDR_GLOBAL(a) \
        ((((__const uint32_t *) (a))[0] & htonl(0x70000000)) \
        == htonl (0x20000000))
#endif /* IS ADDR GLOBAL */

#ifndef IN6_IS_ADDR_ULA
#define IN6_IS_ADDR_ULA(a) \
        ((((__const uint32_t *) (a))[0] & htonl(0xfe000000)) \
        == htonl (0xfc000000))
#endif /* IS ADDR ULA */

the parameter must be taken from ((sockaddr_in6 *)ifa->ifa_addr)->sin6_addr;