After a multicast routing socket is open and multicast forwarding is enabled in the kernel (see
multicast(4)), one of the following socket options should be used to enable or disable PIM processing in the kernel. Note that those options require certain privilege (i.e., root privilege):
/* IPv4 */
int v = 1; /* 1 to enable, or 0 to disable */
setsockopt(mrouter_s4, IPPROTO_IP, MRT_PIM, (void *)&v, sizeof(v));
/* IPv6 */
int v = 1; /* 1 to enable, or 0 to disable */
setsockopt(mrouter_s6, IPPROTO_IPV6, MRT6_PIM, (void *)&v, sizeof(v));
After PIM processing is enabled, the multicast-capable interfaces should be added (see
multicast(4)). In case of PIM-SM, the PIM-Register virtual interface must be added as well. This can be accomplished by using the following options:
/* IPv4 */
struct vifctl vc;
memset(&vc, 0, sizeof(vc));
/* Assign all vifctl fields as appropriate */
...
if (is_pim_register_vif)
vc.vifc_flags |= VIFF_REGISTER;
setsockopt(mrouter_s4, IPPROTO_IP, MRT_ADD_VIF, (void *)&vc,
sizeof(vc));
/* IPv6 */
struct mif6ctl mc;
memset(&mc, 0, sizeof(mc));
/* Assign all mif6ctl fields as appropriate */
...
if (is_pim_register_vif)
mc.mif6c_flags |= MIFF_REGISTER;
setsockopt(mrouter_s6, IPPROTO_IPV6, MRT6_ADD_MIF, (void *)&mc,
sizeof(mc));
Sending or receiving of PIM packets can be accomplished by opening first a “raw socket” (see
socket(2)), with protocol value of
IPPROTO_PIM:
/* IPv4 */
int pim_s4;
pim_s4 = socket(AF_INET, SOCK_RAW, IPPROTO_PIM);
/* IPv6 */
int pim_s6;
pim_s6 = socket(AF_INET6, SOCK_RAW, IPPROTO_PIM);
Then, the following system calls can be used to send or receive PIM packets:
sendto(2),
sendmsg(2),
recvfrom(2),
recvmsg(2).