networking - How to tell which interface the socket received the message from?

Question

If a socket is bound to IN6ADDR_ANY or INADDR_ANY and you use a call such as recvfrom() to receive messages on the socket. Is there a way to find out which interface the message came from?

In the case of IPv6 link-scope messages, I was hoping that the from argument of recvfrom() would have the scope_id field initialized to the interface Id. Unfortunately it is set to 0 in my test program.

Anybody know of a way to find out this information?

Answer 1

dwc is right, IPV6_PKTINFO will work for IPv6 on Linux.

Moreover, IP_PKTINFO will work for IPv4 — you can see details in manpage ip(7)