Re: multicast ping

No, it is up to the impl to do what it wants in isHostReachable(). Yes, 
you cannot use raw sockets in Java, but isReachable() is supposed to use 
ICMP (but unfortunately it is not mandatory). I suggest you check with 
your VM impl and see how it is implemented.

Robert Bowen wrote:
> So can can one be sure ICMP will be used? I've been looking around and 
> most people say Java can't do it because it can't use RAW sockets, etc.
>
> Anyway, does what I said seem to be correct? That since I can't use 
> milticast I'll have to invent (hack) some kind of multi-threaded 
> application that emulates a PING, hopefully with ICMP?
>
> Thanks a bunch,
> Bob
>
> ----- Original Message ----
> From: Bela Ban <belaban@xxxxxxxxx>
> To: Robert Bowen <syg6@xxxxxxxxx>
> Cc: javagroups-users@xxxxxxxxxxxxxxxxxxxxx
> Sent: Wednesday, September 13, 2006 3:37:29 PM
> Subject: Re: [javagroups-users] multicast ping
>
> Note that InetAddress.isReachable() may or may not use ICMP, on Windows
> (SUN's JDK 5), it tries to connect via *TCP* to the echo service (port 9
> IIRC) !! So this is basically unusable.
>
> Robert Bowen wrote:
> > Well, in my case if the service isn't running I simply return a
> > "false" and keep looking for another machine. If after 3 tries I can't
> > find one (or of there are less than 3 machines) it just dies.
> >
> > The problem I am seeing is that since I can't depend on all machines
> > having 124.0.0.1 open, and even if they do, I can't install a listener
> > program on them. So it looks like I'll have to either use ICMP or a
> > simple INetAddress.isReachable() program. But in both cases it would
> > have to be multi-threaded I suppose. That way I can wake up all the
> > threads that run this program at the same time and grab the ip (or id
> > or whatever) of the thread that comes back the quickest ...
> >
> > This is getting complicated! And to think, I thought it was a simple
> > matter of PINGing ...
> >
> > Bob
> >
> > ----- Original Message ----
> > From: Bela Ban <belaban@xxxxxxxxx>
> > To: Robert Bowen <syg6@xxxxxxxxx>
> > Cc: javagroups-users@xxxxxxxxxxxxxxxxxxxxx
> > Sent: Wednesday, September 13, 2006 2:12:32 PM
> > Subject: Re: [javagroups-users] 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 
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> > 
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>
> >
> > >
> > 
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>
> >
> > >
> > > >
> > >
> > 
> <http://sel.as-us.falkag.net/sel?cmd=lnk&kid=120709&bid=263057&dat=121642 
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> > 
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> <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 
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> > 
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> <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> 
>
> > 
> <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> 
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> > 
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> <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> 
>
> > 
> <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> 
>
> > 
> <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> 
>
> > 
> <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> 
>
> > 
> <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
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