java org.javagroups.VersionYou should see the following output (more or less) if the class is found:
Version: 2.0.2
CVS: $Id: INSTALL.html,v 1.15 2003/03/28 20:26:41 belaban Exp $
History: (see doc/history.txt for details)
java org.javagroups.demos.Drawtwice. 2 whiteboard windows should appear. If you started them simultaneously, they should initially show a membership of 1 in their title bars. After some time, both windows should show 2. This means that the two instances found each other and formed a group.
When drawing in one window, the second instance should also be updated. As the default group transport uses IP multicast, make sure that - if you want to start the 2 instances in different subnets - IP multicast is enabled. If this is not the case, the 2 instances won't 'find' each other and the sample won't work.
You can change the properties of the demo to for example use a different
transport if multicast doesn't work (it should always work on the same
machine). Please consult the documentation to see how to do this.
route add -net 224.0.0.0 netmask 224.0.0.0 dev loThis means that all traffic directed to the 224.0.0.0 network will be sent to the loopback interface, which means it doesn't need any network to be running. Note that the 224.0.0.0 network is a placeholder for all multicast addresses in most UNIX implementations: it will catch allmulticast traffic. This is an undocumented feature of /sbin/route and may not work across all UNIX flavors. The above instructions may also work for Windows systems, but this hasn't been tested. Note that not all systems allow multicast traffic to use the loopback interface.
Typical home networks have a gateway/firewall with 2 NICs: the first (eth0)
is connected to the outside world (Internet Service Provider), the second
(eth1) to the internal network, with the gateway firewalling/masquerading
traffic between the internal and external networks. If no route for multicast
traffic is added, the default will be to use the fdefault gateway, which
will typically direct the multicast traffic towards the ISP. To prevent
this (e.g. ISP drops multicast traffic, or latency is too high), we recommend
to add a route for multicast traffic which goes to the internal network
(e.g. eth1).
java org.javagroups.tests.McastReceiverTest -mcast_addr 224.10.10.10 -port 5555Then start McastSenderTest:
java org.javagroups.tests.McastSenderTest -mcast_addr 224.10.10.10 -port 5555You should be able to type in the McastSenderTest window and see the output in the McastReceiverWindow. If not, try to use -ttl 32 in the sender. If this still fails, consult a system administrator to help you setup IP multicast correctly. If you are the system administrator, look for another job :-)
Other means of getting help: there is a public forum on javagroups.sf.net for questions. Also consider subscribing to the javagroups-users mailing list to discuss such and other problems.
In this case we have to use a sledgehammer (running only under JDK 1.4. and higher): we can enable the above sender and receiver test to use all available interfaces for sending and receiving. One of them will certainly be the right one... Start the receiver as follows:
java org.javagroups.tests.McastReceiverTest1_4 -mcast_addr 228.8.8.8 -use_all_interfaces
The multicast receiver uses the 1.4 functionality to list all available
network interfaces and bind to all of them (including the loopback
interface). This means that whichever interface a packet comes in on, we
will receive it.
Now start the sender:
java org.javagroups.tests.McastSenderTest1_4 -mcast_addr 228.8.8.8 -use_all_interfaces
The sender will also determine the available network interfaces and send each packet over all interfaces.
This test can be used to find out which network interface to bind to when previously no packets were received. E.g. when you see the following output in the receiver:
bash-2.03$ java org.javagroups.tests.McastReceiverTest1_4 -mcast_addr 228.8.8.8 -bind_addr 192.168.168.4
Socket=0.0.0.0/0.0.0.0:5555, bind interface=/192.168.168.4
dd [sender=192.168.168.4:5555]
dd [sender=192.168.168.1:5555]
dd [sender=192.168.168.2:5555]
you know that you can bind to any of the 192.168.168.{1,2,4} interfaces to receive your multicast packets. In this case you would need to modify your protocol spec to include bind_addr=192.168.168.2 in UDP, e.g. "UDP(mcast_addr=228.8.8.8;bind_addr=192.168.168.2):..." .
Alternatively you can use McastDiscovery1_4 (runs only on JDK 1.4). Start
this program simultaneously on multiple machines. Binding to all available
interfaces, this program tries to discover what other members are available
in a network and determines which interfaces should be used by UDP. After
some time (e.g. 30 seconds), press <enter> on each program. The program
will then list the interfaces which can be used to bind to. There may be
one or multiple interfaces. When there are multiple interfaces listed, take
the one with the highest number of responses (at the top of the list). The
UDP protocol spec can then be changed to explicitly bind to that interface,
e.g.
"UDP(bind_addr=<interface>;...)"
Another source of problems might be the use of IPv6, and/or misconfiguration
of /etc/hosts. If you communicate between an IPv4 and an IPv6 host,
and they are not able to find each other, try the java.net.preferIP4Stack=true
property, e.g.
java -Djava.net.preferIPv4Stack=true org.javagroups.demos.Draw -props
file:c:\\default.xml
JDK 1.4.1 uses IPv6 by default, although is has a dual stack, that is,
it also supports IPv4. Here's more
details on the subject.