Linux netlink mutlicast routing updates

Question

My application should get netlink multicast route updates from kernel. I did some research and found mutlicast uses different family:RTNL_FAMILY_IPMR and group is RTMGRP_IPV4_MROUTE.

However if I use:

    sfd = socket (AF_NETLINK, SOCK_RAW, NETLINK_ROUTE);
    snl.nl_groups |= RTMGRP_IPV4_MROUTE

I dont get any updates.

But

    sfd = socket (AF_NETLINK, SOCK_RAW, NETLINK_ROUTE);
    snl.nl_family = RTNL_FAMILY_IPMR;
    snl.nl_groups |= RTMGRP_IPV4_MROUTE;

This give bind error", bind: Invalid argument

    sfd = socket (RTNL_FAMILY_IPMR, SOCK_RAW, NETLINK_ROUTE);

This give "Address family not supported by protocol" error

I'm not sure how to get updates from kernel for mutlicast routes.

score 0 · Answer 1 · answered Apr 22 '16 at 10:44

copy-paste from earlier project I have:

    struct sockaddr_nl naddr;

    netlinkfd = socket (AF_NETLINK, SOCK_RAW, NETLINK_ROUTE);
    naddr.nl_family = AF_NETLINK;
    naddr.nl_groups = (1 << (RTNLGRP_LINK - 1)) |
                      (1 << (RTNLGRP_IPV4_ROUTE - 1)) |
                      (1 << (RTNLGRP_IPV6_ROUTE - 1)) |
                      (1 << (RTNLGRP_IPV4_IFADDR - 1)) |
                      (1 << (RTNLGRP_IPV6_IFADDR -1 ));
    if (bind (netlinkfd, (struct sockaddr *)&naddr, sizeof (naddr)))
    {
        error_foo();
        return;
    }

This one works for me receiving link, ip and routing table in general. (pushing me all the changes from this point of - if I want to receive the current status, I need to request them aswell). Try to have both ROUTE and MROUTE since you want multicast routing tables, but they might be merged into the normal routing table

Linux netlink mutlicast routing updates

1 Answers1