How to get destination address of UDP packet?
 

Hello,
I need to know destination address of incoming UDP packet, while sockets API (recvfrom) only provide sender address.
How to do that?

err, shouldn't the destination address be the address of the machine running the program?, there may be methods to allow you to peer further down the stack if there is a question of multiple interfaces.

I receive multicast packets, destination address of such packet is a multicast group address. That's the thing I want to know - address of multicast group received packet was sent to.

ok, try this, use the recvfrom (check on the man pages) call to receive the data. This will give you a sockaddr pointer containing the data about the incoming connection. The sockaddr structure contains a sa_data member which is simply a 14 byte char array. Somewhere in this array is the data you need.

crap, now I see what you mean, ok, sratch that.

ok, look at "man 7 ip". In there is an option called IP_PKTINFO. This gives some info about the ip packet, including the header destination address.

First set IP_PKTINFO using setsockpt. Then when the data is recieved, use recvmsg to extract the packet information, which should contain the destination address in the header. This only works for datagram/udp transactions. Let me know how you get on, as I've never done this.

Thanks, this works fine.
I use recvmsg function to read from socket and receive struct in_pktinfo via msg_control member of struct msghdr. The only thing is I have to pass 24-byte buffer as msg_control (not 12-byte that gives sizeof(struct in_pktinfo)) and use latter 12 bytes of that buffer as struct in_pktinfo after successful call to recvmsg. I use Red Hat Enterprise Linux AS release 4 (Nahant Update 4).

I got the destination address using ip_pktinfo in multicast program but how do i get the source address from the header. i tried struct msg_hdr->msg_name and pktinfo->ipi_spec_dest. both are giving the same multicast address returned in pktinfo->ipi_addr. how do get the source ip address ?