I would like to have the client detect a server on a lan. So there will
be some 30 clients on the same lan as a single server and when they start
I want them to be able to find the server and automatically connect to it
for using RMI.

My idea was to have them send out a UDP packet to the broadcast address
and then have the server respond saying, "Here I am!", but I'm having
difficulty figuring out how to send a UDP packet to the broadcast address
of the lan.

I tried just sending it to "255.255.255.255", but this didn't work. Is
there a way to detect the broadcast address? Is there a way to send a
packet to it? Is there a simpler way to do what I'm trying to do?

Thanks.



--
Ken T.
http://www.electricsenator.net

As we enjoy great advantages from the inventions of others, we should
be glad of an opportunity to serve others by any invention of ours.
-- Benjamin Franklin

Ken T. wrote:
> I would like to have the client detect a server on a lan. So there will
> be some 30 clients on the same lan as a single server and when they start
> I want them to be able to find the server and automatically connect to it
> for using RMI.
>
> My idea was to have them send out a UDP packet to the broadcast address
> and then have the server respond saying, "Here I am!", but I'm having
> difficulty figuring out how to send a UDP packet to the broadcast address
> of the lan.
>
> I tried just sending it to "255.255.255.255", but this didn't work. Is
> there a way to detect the broadcast address? Is there a way to send a
> packet to it? Is there a simpler way to do what I'm trying to do?
>
> Thanks.

You can't just try to connect to the server?

--

Knute Johnson
email s/nospam/knute2009/

--
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On 02 Jul 2009 03:30:34 GMT, "Ken T." <nowhere@home.com> wrote, quoted
or indirectly quoted someone who said :

> Is there a simpler way to do what I'm trying to do?

I would implement some trivial transaction on the server, e.g.
what version are you? are you alive?

Then just send that as a GET HTTP packet.
--
Roedy Green Canadian Mind Products
http://mindprod.com

"Deer hunting would be fine sport, if only the deer had guns."
~ William S. Gilbert of Gilbert and Sullivan

On Wed, 01 Jul 2009 21:28:57 -0700, Knute Johnson wrote:

> Ken T. wrote:
>> I would like to have the client detect a server on a lan. So there
>> will be some 30 clients on the same lan as a single server and when
>> they start I want them to be able to find the server and automatically
>> connect to it for using RMI.
>>
>> My idea was to have them send out a UDP packet to the broadcast address
>> and then have the server respond saying, "Here I am!", but I'm having
>> difficulty figuring out how to send a UDP packet to the broadcast
>> address of the lan.
>>
>> I tried just sending it to "255.255.255.255", but this didn't work. Is
>> there a way to detect the broadcast address? Is there a way to send a
>> packet to it? Is there a simpler way to do what I'm trying to do?
>>
>> Thanks.
>
> You can't just try to connect to the server?

That's the thing.. I don't know its IP address. I want to detect it.




--
Ken T.
http://www.electricsenator.net

The only two things that are infinite in size are the universe and
human stupidity. And I'm not completely sure about the universe.
-- Albert Einstein

On Wed, 01 Jul 2009 23:29:23 -0700, Roedy Green wrote:

> On 02 Jul 2009 03:30:34 GMT, "Ken T." <nowhere@home.com> wrote, quoted
> or indirectly quoted someone who said :
>
>> Is there a simpler way to do what I'm trying to do?
>
> I would implement some trivial transaction on the server, e.g. what
> version are you? are you alive?
>
> Then just send that as a GET HTTP packet.

OK, this isn't a web server. This is a server I'm writing for part of
the program. I won't know what machine it is running on. So what I'm
trying to do is to detect what the ip address of the server is.

The idea was that a client would scream out

"Marco"

on a broadcast address, and the server would answer,

"Polo"

by sending a UDP packet back to the client, thereby giving the client its
IP address.

If there is a better way to do this, please let me know.

Thanks.

--
Ken T.
http://www.electricsenator.net

The optimist thinks this is the best of all possible worlds. The
pessimist fears it is true.
-- Robert Oppenheimer

Ken T. wrote:
> I would like to have the client detect a server on a lan. [...]
>
> My idea was to have them send out a UDP packet to the broadcast address
> and then have the server respond saying, "Here I am!", but I'm having
> difficulty figuring out how to send a UDP packet to the broadcast address
> of the lan.

I've not tried this, but I'd look at:

<http://java.sun.com/javase/6/docs/api/java/net/InterfaceAddress.html#getBroadcast%28%29>

Get the InterfaceAddress for the NetworkInterface connected to the LAN
to want to broadcast on. If you have no criteria for choosing one, you
could try them all.

--
ss at comp dot lancs dot ac dot uk

Ken T. wrote:

> I would like to have the client detect a server on a lan. So there will
> be some 30 clients on the same lan as a single server and when they start
> I want them to be able to find the server and automatically connect to it
> for using RMI.
>
> My idea was to have them send out a UDP packet to the broadcast address
> and then have the server respond saying, "Here I am!", but I'm having
> difficulty figuring out how to send a UDP packet to the broadcast address
> of the lan.
>
> I tried just sending it to "255.255.255.255", but this didn't work. Is
> there a way to detect the broadcast address? Is there a way to send a
> packet to it? Is there a simpler way to do what I'm trying to do?

Use the rmiregistry. That's what it's for.

--
Nigel Wade

In article <4a4c5b40$0$24741$ec3e2dad@news.usenetmonster.com> ,
"Ken T." <nowhere@home.com> wrote:

> On Wed, 01 Jul 2009 21:28:57 -0700, Knute Johnson wrote:
>
> > Ken T. wrote:
> >> I would like to have the client detect a server on a lan. So there
> >> will be some 30 clients on the same lan as a single server and when
> >> they start I want them to be able to find the server and automatically
> >> connect to it for using RMI.
> >>
> >> My idea was to have them send out a UDP packet to the broadcast address
> >> and then have the server respond saying, "Here I am!", but I'm having
> >> difficulty figuring out how to send a UDP packet to the broadcast
> >> address of the lan.
> >>
> >> I tried just sending it to "255.255.255.255", but this didn't work. Is
> >> there a way to detect the broadcast address? Is there a way to send a
> >> packet to it? Is there a simpler way to do what I'm trying to do?
> >
> > You can't just try to connect to the server?
>
> That's the thing.. I don't know its IP address. I want to detect it.

You might look into zeroconf/bonjour:

<http://en.wikipedia.org/wiki/Multicast_DNS>

--
John B. Matthews
trashgod at gmail dot com
<http://sites.google.com/site/drjohnbmatthews>

Ken T. wrote:
> On Wed, 01 Jul 2009 21:28:57 -0700, Knute Johnson wrote:
>
>> Ken T. wrote:
>>> I would like to have the client detect a server on a lan. So there
>>> will be some 30 clients on the same lan as a single server and when
>>> they start I want them to be able to find the server and automatically
>>> connect to it for using RMI.
>>>
>>> My idea was to have them send out a UDP packet to the broadcast address
>>> and then have the server respond saying, "Here I am!", but I'm having
>>> difficulty figuring out how to send a UDP packet to the broadcast
>>> address of the lan.
>>>
>>> I tried just sending it to "255.255.255.255", but this didn't work. Is
>>> there a way to detect the broadcast address? Is there a way to send a
>>> packet to it? Is there a simpler way to do what I'm trying to do?
>>>
>>> Thanks.
>> You can't just try to connect to the server?
>
> That's the thing.. I don't know its IP address. I want to detect it.
>
>
>
>

OK, I understand what you are asking now. The UDP packet idea sounds
pretty simple. Just have the server broadcast to a specific address and
port with its IP address. The clients can read the UDP packets and
connect to the sent address. There is a range for multicast addresses,
take a look at the class MulticastSocket. It has all the details and if
you know how to do UDP datagrams in Java you should be good to go.

--

Knute Johnson
email s/nospam/knute2009/

--
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On Thu, 02 Jul 2009 11:59:11 +0100, Nigel Wade wrote:

> Ken T. wrote:
>
>> I would like to have the client detect a server on a lan. So there
>> will be some 30 clients on the same lan as a single server and when
>> they start I want them to be able to find the server and automatically
>> connect to it for using RMI.
>>
>> My idea was to have them send out a UDP packet to the broadcast address
>> and then have the server respond saying, "Here I am!", but I'm having
>> difficulty figuring out how to send a UDP packet to the broadcast
>> address of the lan.
>>
>> I tried just sending it to "255.255.255.255", but this didn't work. Is
>> there a way to detect the broadcast address? Is there a way to send a
>> packet to it? Is there a simpler way to do what I'm trying to do?
>
> Use the rmiregistry. That's what it's for.

That just pushes the problem one more step away...

How do I find the rmiregistry?

--
Ken T.
http://www.electricsenator.net

There are 10 types of people in this world: those who understand
binary and those who don't.