Re: UDP broadcast/receive notification system

On Fri, 18 Jul 2008 12:07:01 -0700, Mark <mmodrall@xxxxxxxxxxxxx> wrote:

[...]
In his classes, he prefaces each broadcast message with a guid so that when
a message comes in he can check to see if it's one he just sent. This
spurred a couple of questions for me:
1) I haven't yet seen a message I drop on the broadcast address come back on
my receiver socket. Was this just speculative overkill on his part?

Are you sure that's all he's using it for? He may be also (or instead) using the GUID to detect duplicated datagrams at the recipient end.

My recollection is that the sending socket won't get echos, so if that's all he's doing, yes...that's probably overkill. But it's possible that's not all he's doing.

2) Now I know this sounds a little daft, but he purposely set it up so that
multiple processes on the same box can both broadcast and receive. Would I
see the message coming from my box on one of the other processes (if I get
one started up) that's listening on the same port?

Unless you bind to different IP addresses, you wouldn't be able to receive on the same port (I prefer not to use the word "listen" when talking about UDP, because it has a more specialized meaning in the context of TCP). You wouldn't be able to create the socket unless you specifically say that you want to reuse the address, and even reusing the address is not necessarily going to allow two different sockets to both receive data on the same port.

But yes, assuming you explicitly bind to two different IP addresses, you could have one process send a datagram, and another process on the same computer receive that datagram.

Pete
.

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