Get multicast addresses from interface

[Grigory Klyuchnikov]

Hello,
How can a user process get IPv6 multicast addresses of ethernet
interfaces? I have FreeBSD 5.2.1 and get interface addresses
via ioctl(SIOCGIFCONF) or sysctl(witch NET_RT_IFLIST),
but all returned addresses are unicast.
In net/if.h there is a struct ifma_msghdr:
/*
 * Message format for use in obtaining information about multicast addresses
 * from the routing socket
 */
struct ifma_msghdr {
u_short ifmam_msglen;   /* to skip over non-understood messages */
u_char  ifmam_version;  /* future binary compatibility */
u_char  ifmam_type; /* message type */
int ifmam_addrs;/* like rtm_addrs */
int ifmam_flags;/* value of ifa_flags */
u_short ifmam_index;/* index for associated ifp */
};
How it may be used?
Regards,
Grigory Klyuchnikov.
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Re: Get multicast addresses from interface

[Brooks Davis]

On Thu, Oct 14, 2004 at 05:44:57PM +0400, Grigory Klyuchnikov wrote:
 Hello,
 
 How can a user process get IPv6 multicast addresses of ethernet
 interfaces? I have FreeBSD 5.2.1 and get interface addresses
 via ioctl(SIOCGIFCONF) or sysctl(witch NET_RT_IFLIST),
 but all returned addresses are unicast.

getifaddrs(3) and getifmaddrs(3) may do what you want.

 In net/if.h there is a struct ifma_msghdr:
 
 /*
  * Message format for use in obtaining information about multicast addresses
  * from the routing socket
  */
 struct ifma_msghdr {
   u_short ifmam_msglen;   /* to skip over non-understood messages */
   u_char  ifmam_version;  /* future binary compatibility */
   u_char  ifmam_type; /* message type */
   int ifmam_addrs;/* like rtm_addrs */
   int ifmam_flags;/* value of ifa_flags */
   u_short ifmam_index;/* index for associated ifp */
 };
 
 
 How it may be used?

In addition to the functions above, you can directly access these
structures via sysctl (see src/lib/libc/net/getifmaddrs.c for an
example).

-- Brooks

-- 
Any statement of the form X is the one, true Y is FALSE.
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Re: Get multicast addresses from interface

[Bruce M Simpson]

On Thu, Oct 14, 2004 at 08:01:49AM -0700, Brooks Davis wrote:
 On Thu, Oct 14, 2004 at 05:44:57PM +0400, Grigory Klyuchnikov wrote:
  How can a user process get IPv6 multicast addresses of ethernet
  interfaces? I have FreeBSD 5.2.1 and get interface addresses
  via ioctl(SIOCGIFCONF) or sysctl(witch NET_RT_IFLIST),
  but all returned addresses are unicast.
 
 getifaddrs(3) and getifmaddrs(3) may do what you want.

See http://people.freebsd.org/~bms/dump/mcastlist/ for the original
code (harti@ submitted most of the kernel bits).

I didn't specifically set out to test getifmaddrs(3) with AF_INET6
addresses when I wrote it, but I seem to recall that it should work
with them, from testing.

If not, please feel free to submit a PR with a patch.

Thanks,
BMS


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