如何绑定/连接多个UDP套接字

Question

My initial UDP socket is binded to 127.0.0.1:9898.

The first time that I get notified of incoming data by epoll/kqueue, I do recvfrom() and I fill a struct sockaddr called peer_name that contain the peer informations (ip:port).

Then I create a new UPD socket using socket(),

then I bind() this newly created socket to the same ip:port (127.0.0.1:9898) than my original socket.

then I connect my newly created socket using connect() to the peer who just sent me something. I have the information in the struct sockaddr called peer_name .

I then add my newly created socket in my epoll/kqueue vector and wait for notification.

I would expect to ONLY receive UDP frame from the peer i'm ""connected to"".

1/ does netstat -a -p udp is suppose to show me the IP:PORT of the peer my newly created socket is ""connected to"" ?

2/ I'm probably doing something wrong since after creating my new socket, this socket receive all incoming UDP packets destinated to the IP:PORT I'm binded to, regardless of the source peer IP:PORT.

I would like to see a working example of what I'm trying to do :) or any hint on what I'm doing wrong.

thanks!

Answer 1

http://www.softlab.ntua.gr/facilities/documentation/unix/unix-socket-faq/unix-socket-faq-5.html

"Does doing a connect() call affect the receive behaviourof the socket? Yes, in two ways. First, only datagrams from your "connected peer" are returned. All others arriving at your port are not delivered to you.

But most importantly, a UDP socket must be connected to receive ICMP errors. Pp. 748-749 of "TCP/IP Illustrated, Volume 2" give all the gory details on why this is so."

Answer 2

connect(2) on a UDP socket just sets the default destination address of the socket (where the data will be sent if you use write(2) or send(2) on the socket). It has no other effect -- you can still send packets to other addresses with sendto(2) or sendmsg(2) and you'll still see packets sent from any address.

So it doesn't really make any sense to open a new socket on the port -- for every packet received, you need to look at the source address to see if it comes from an address you've seen already (and thus belongs to that logical stream) or is a new address (a new logical stream).