OS X equivalent of SO_BINDTODEVICE

Question

Linux allows to execute following code to bind a socket to some specific network interface. So, the data sent through this socket will always be channeled through the original interface.

setsockopt(socket, SOL_SOCKET, SO_BINDTODEVICE, name, strlen(name))

As I understand, this functionality is used in VPN clients. A socket gets connected to a remote server and bound to a network interface. This way, the traffic from VPN client itself won't be looped back into VPN client.

Is there OS X equivalent of doing this? Either

• Binding a socket to some specific interface

• Marking a socket in VPN client to not be looped back.

BTW. I found similar question, but I didn't understand the answer: Writing an OS X kernel extension to implement Linux's SO_BINDTODEVICE socket option

Update 1

I found out that some of VPN clients use TUN/TAP devices to prevent loopback problem. http://backreference.org/2010/03/26/tuntap-interface-tutorial/

However, I am not that that all OS X VPN uses that.

Answer 1

Yep, use IP_BOUND_IF

int idx = if_nametoindex("en0");
setsockopt(sockfd, IPPROTO_IP, IP_BOUND_IF, &idx, sizeof(idx))

However, you can just use bind() with the IP address of the interface instead, that's often easier.