On Wed, Jul 18, 2018 at 10:10 AM, Bednár Martin <martin@xxxxxxxxxxx> wrote: > > Hi, > > I'm trying to implement `ip route get x.x.x.x` functionality in C. > I understand this command asks the kernel to resolve the route/gateway > for a concrete address and report it to userspace. Please correct me if > I'm wrong. > > I'm trying to do this in C using the libnl-route API, but don't see any > combination of functions to achieve it. > I have managed to get the default route by filtering a zero address from > the cache. But I'm stumped at submitting a concrete address to look up... > Could anyone point me in the right direction? > Hi! I've recently implemented such feature in my code using libmnl and following this example: http://git.netfilter.org/libmnl/tree/examples/rtnl/rtnl-route-dump.c Firstly, you've to create a header with type RTM_GETROUTE and flag NLM_F_REQUEST. Later, an extra header like: rtm->rtm_family = AF_INET; rtm->rtm_dst_len = 32; rtm->rtm_src_len = 0; rtm->rtm_tos = 0; rtm->rtm_protocol = RTPROT_UNSPEC; rtm->rtm_table = RT_TABLE_UNSPEC; rtm->rtm_type = RTN_UNSPEC; rtm->rtm_scope = RT_SCOPE_UNIVERSE; rtm->rtm_flags = RTM_F_LOOKUP_TABLE; And finally, add an attribute with mnl_attr_put() inserting the RTA_DST with the destination IP address. All this will generate a netlink request that gets the routing info for such destination address. Hope this helps, Regards! -- To unsubscribe from this list: send the line "unsubscribe netfilter" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
