Included with Coherence is a Multicast Test utility, which helps you determine if multicast is enabled between two or more computers. This is a connectivity test, not a load test, each instance will by default only transmit a single multicast packet once every two seconds. For network load testing please see the Datagram Test.
To run the Multicast Test utility use the following syntax from the command line:
|-local||True|| The address of the NIC to transmit on, specified as an IP address
|-group||True|| The multicast address to use, specified as IP:port.
|-ttl||True|| The time to live for multicast packets.
|-delay||True|| The delay between transmitting packets, specified in seconds.
|-display||True|| The number of bytes to dispaly from unexpected packets.
For ease of use, multicast-test.sh and multicast-test.cmd scripts are provided in the Coherence bin directory, and can be used to execute this test.
Note: prior to Coherence 3.1 the following syntax was used, and scripts were not provided:
Let's say that we want to test if we can use multicast address 220.127.116.11, port 9000 (the test's defaults) to send messages between two servers - Server A with IP address 18.104.22.168 and Server B with IP address 22.214.171.124.
Starting with Server A, let's determine if it has multicast address 126.96.36.199 port 9000 available for 188.8.131.52 by first checking the machine or interface by itself as follows:
From a command session, type in:
After pressing ENTER, you should see the Multicast Test utility showing you how it is sending sequential multicast packets and receiving them as follows:
Once you have seen a number of these packets sent and received successfully, you can hit CTRL-C to stop further testing.
If you do not see something similar to the above, then multicast is not working. Also, please note that we specified a TTL of 0 to prevent the multicast packets from leaving Server A.
You can repeat the same test on Server B to assure that it too has the multicast enabled for it's port combination.
Now to test multicast communications between Server A and Server B. For this test we will use a non-zero TTL which will allow the packets to leave their respective servers. By default the test will use a TTL of 4, if you believe that there may be more network hops required to route packets between Server A and Server B, you may specify a higher TTL value.
Start the test on Server A and Server B by entering the following command into the command windows and pressing ENTER:
You should see something like the following on Server A:
and something like the following on Server B:
You can see that both Server A and Server B are issuing multicast packets and seeing their own and each other's packets. This indicates that multicast is functioning properly between these servers using the default multicast address and port.
Note: Server A sees only its own packets 1-4 until we start Server B and it receives packet 1 from Server B.
If you are unable to establish bidirectional multicast communication please try the following:
Where eth1 is the device which will be designated to transmit multicast traffic.
If multicast is not functioning properly, you will need to consult with your network administrator or sysadmin to determine the cause and to correct the situation.