Re: multicast ping

224.0.0.1/2 are IANA defined addresses, for multicast discovery. But 
most hosts discard packets anyway. Yes, if you know you have a service 
running, you can of course probe its port, e.g. 8080 for JBoss. But what 
if you service (e.g. echo service on port 9) is not running ?

Robert Bowen wrote:
> 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 not
> 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
> >
> > 
> -------------------------------------------------------------------------
> > Using Tomcat but need to do more? Need to support web services, 
> security?
> > Get stuff done quickly with pre-integrated technology to make your job
> > easier
> > Download IBM WebSphere Application Server v.1.0.1 based on Apache 
> Geronimo
> > 
> http://sel.as-us.falkag.net/sel?cmd=lnk&kid=120709&bid=263057&dat=121642 
> <http://sel.as-us.falkag.net/sel?cmd=lnk&kid=120709&bid=263057&dat=121642> 
>
> > 
> <http://sel.as-us.falkag.net/sel?cmd=lnk&kid=120709&bid=263057&dat=121642 
> <http://sel.as-us.falkag.net/sel?cmd=lnk&kid=120709&bid=263057&dat=121642>>
> > _______________________________________________
> > javagroups-users mailing list
> > javagroups-users@xxxxxxxxxxxxxxxxxxxxx
> > https://lists.sourceforge.net/lists/listinfo/javagroups-users
> >
> > ------------------------------------------------------------------------
> >
> > 
> -------------------------------------------------------------------------
> > Using Tomcat but need to do more? Need to support web services, 
> security?
> > Get stuff done quickly with pre-integrated technology to make your 
> job easier
> > Download IBM WebSphere Application Server v.1.0.1 based on Apache 
> Geronimo
> > 
> http://sel.as-us.falkag.net/sel?cmd=lnk&kid=120709&bid=263057&dat=121642 
> <http://sel.as-us.falkag.net/sel?cmd=lnk&kid=120709&bid=263057&dat=121642>
> > ------------------------------------------------------------------------
> >
> > _______________________________________________
> > javagroups-users mailing list
> > javagroups-users@xxxxxxxxxxxxxxxxxxxxx
> > https://lists.sourceforge.net/lists/listinfo/javagroups-users
> >  
>
> -- 
> Bela Ban
> Lead JGroups / Manager JBoss Clustering Group
> JBoss - a division of Red Hat
>
>
> -------------------------------------------------------------------------
> Using Tomcat but need to do more? Need to support web services, security?
> Get stuff done quickly with pre-integrated technology to make your job 
> easier
> Download IBM WebSphere Application Server v.1.0.1 based on Apache Geronimo
> http://sel.as-us.falkag.net/sel?cmd=lnk&kid=120709&bid=263057&dat=121642 
> <http://sel.as-us.falkag.net/sel?cmd=lnk&kid=120709&bid=263057&dat=121642>
> _______________________________________________
> javagroups-users mailing list
> javagroups-users@xxxxxxxxxxxxxxxxxxxxx
> https://lists.sourceforge.net/lists/listinfo/javagroups-users
>
> ------------------------------------------------------------------------
>
> -------------------------------------------------------------------------
> Using Tomcat but need to do more? Need to support web services, security?
> Get stuff done quickly with pre-integrated technology to make your job easier
> Download IBM WebSphere Application Server v.1.0.1 based on Apache Geronimo
> http://sel.as-us.falkag.net/sel?cmd=lnk&kid=120709&bid=263057&dat=121642
> ------------------------------------------------------------------------
>
> _______________________________________________
> javagroups-users mailing list
> javagroups-users@xxxxxxxxxxxxxxxxxxxxx
> https://lists.sourceforge.net/lists/listinfo/javagroups-users
>   

-- 
Bela Ban
Lead JGroups / Manager JBoss Clustering Group
JBoss - a division of Red Hat


-------------------------------------------------------------------------
Using Tomcat but need to do more? Need to support web services, security?
Get stuff done quickly with pre-integrated technology to make your job easier
Download IBM WebSphere Application Server v.1.0.1 based on Apache Geronimo
http://sel.as-us.falkag.net/sel?cmd=lnk&kid=120709&bid=263057&dat=121642