Re: Can I use same port for sending and receiving in UDP

"AliR \(VC++ MVP\)" <AliR@online.nospam>
Thu, 2 Apr 2009 16:22:14 -0500
I think I had UPD and Multicast behavior mixed up. I just went back through
some old code, if you broadcast on a UDP port, and the socket is also
created on the same port, then it will receive it;s own message. On
Multicast the loopback flag must be set in order for the sender to receive
the same message it just broadcasted out.


"Joseph M. Newcomer" <> wrote in message

Consider the following:

App A (server):

recvfrom(port, ...);
sendto(port, ...)

App B (client)

sendto(port, ...);
recvfrom(port, ...);

Now, if A sends a message to B on port NNNNN, and then does a rcvfrom on
port NNNNN, why
doesn't it get its own message back? Why would app B get it?

Just curious. I don't know the answer. My reading had suggest that the
way the network
stacks route messages to applications is that the port is associated with
a unique


On Thu, 2 Apr 2009 14:21:27 -0500, "AliR \(VC++ MVP\)"
<AliR@online.nospam> wrote:

You can send a packet to any port you want from a UDP socket. The fact
the recipient would get it or not is unknown at that point. Just because
message came through a specific UDP port does not mean that the sender is
listening to messages on that same port.


"Stephen Myers" <> wrote in message

I believe what's going on is there is one known port. Once a message is
received using RecvFrom(), you can send replies to that port.


"Tom Serface" wrote:

Often they are yes, but the client is typically an application and the
server a service. Not sure if that makes any difference.


"Joseph M. Newcomer" <> wrote in message

Are both client and server running on the same machine?

On Wed, 1 Apr 2009 13:44:43 -0700, "Tom Serface" <>

We use the same port for listening and sending in several of our
applications and it works fine. I'm not sure this is "standard" or
anything, but the applications have been working well for a long time
ports are hard to register with firewalls, etc. so we try to minimize
one's we use.


"Joseph M. Newcomer" <> wrote in message

A port is associated with a single application. A single
use the same
port to both send and receive, but I do not think it is supported
both. Think of this
as client and server; the client and server ports must be

On Tue, 31 Mar 2009 22:46:51 -0700 (PDT), Faisal


I've an application which uses UDP Sockets for IPC.

My application communicates with another application through UDP
sockets. A fixed port number is used for this. Now I want to
the data send by the other application. Both application runs in
same machine. Can I use the same UDP port for sending and

If so, is there any chance that the data sent by my application is
received by itself?

Joseph M. Newcomer [MVP]
MVP Tips:

Joseph M. Newcomer [MVP]
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Joseph M. Newcomer [MVP]
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