Re: multicast ping

Hmmm. I don't know much about ICMP. Would you mind elaborating a bit on what you mean by "use ICMP"? I did find a Java implementation of it over at koders.com, but I'm still poking around ...

I read in the java forums that it probably makes more sense to query a particular service on a machine rather than try to send a PING. After all, if the machine is up but Tomcat or our servlet is down, it's of no use to the app.

But regardless, if I want to send a multicast message, using Java's MulticastSocket or JGroups, the machines have to have port 124.0.0.1 open and some kind of Multicast client listening, otherwise they won't get the message, correct?

Is there no way to define an Array (or Vector, like JGroups) of ips and send a multicast message to all of them, *without* them having a client running? If I were able to create a Java class that sends an ICMP message to each ip in my list (assuming each machine responds to ICMP) that would be the way to go, no? The "client" on each machine would be an ICMP listener.

Perhaps I can make this a requirement, that all machines that want be be clients have to listen for ICMP packets. I have to look into this some more ...

Many thanks!
Bob

----- Original Message ----
From: Bela Ban <belaban@xxxxxxxxx>
To: Robert Bowen <syg6@xxxxxxxxx>
Cc: javagroups-users@xxxxxxxxxxxxxxxxxxxxx
Sent: Wednesday, September 13, 2006 12:38:45 PM
Subject: Re: [javagroups-users] multicast ping

I think your only hope then is to use ICMP. However, machines are no t
obliged to respond to ICMP. The official ping address for hosts is
224.0.0.1 and for routers 224.0.0.2 IIRC.

Robert Bowen wrote:
> Thanks for your responses. There's a little detail I left out of my
> last email (because I didn't know it ...) -- these machines that I
> want to PING are *not* ours. They are machines that our app will send
> requests to but we don't have any control over them. Which means I
> can't put a JGroups client on each machine that listens for PINGs and
> responds.
>
> So I guess I am stuck with Bela's recommendation, to make some "simple
> multicasting code", without JGroups, because the other recommendations
> -- using MessageDispatcher.castMessage() or using JGroups with
> bare-bones.xml -- both require a JGroups client listening on each machine.
>
> So I guess I'll just start searching for plain-old java.net code. :(
>
> This is the second time I've tried to work JGroups into this project
> and each time, because of project specs, we haven't used it. Bummer.
>
> Thanks,
> Bob
>
> ----- Original Message ----
> From: Bela Ban <belaban@xxxxxxxxx>
> To: Robert Bowen <syg6@xxxxxxxxx>
> Cc: javagroups-users@xxxxxxxxxxxxxxxxxxxxx
> Sent: Tuesday, September 12, 2006 10:10:41 PM
> Subject: Re: [javagroups-users] multicast ping
>
> You could do this with simple multicasting code, or you could use
> JGroups (with the bare-bones.xml config) to simply send out a multicast
> and wait for the first reply. So, no, you don't need to rip out some
> JGroups-internal code and use it in your project, but you could simply
> use a JChannel to do that.
>
> Robert Bowen wrote:
> > Hello all.
> >
> > I've been out of the JGroups loop for a while but diligently perusing
> > the mailing list.
> >
> > I had a question about an app I need to write. What I need to do is,
> > in a given moment send out a multicast "ping" and return the ip of the
> > first machine that answers. I know that internally this is what
> > JGroups does to keep an updated list of "alive" machines. My question
> > is, can I use the same internal mechanism JGroups uses? I don't think
> > so, not without deconstructing the code.
> >
> > The other option is to send out my own multicast message, but if I'm
> > not mistaken, multicast messages don't send back responses.
> >
> > Any thoughts?
>
> --
> Bela Ban
> Lead JGroups / Manager JBoss Clustering Group
> JBoss - a division of Red Hat
>
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--
Bela Ban
Lead JGroups / Manager JBoss Clustering Group
JBoss - a division of Red Hat


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