Multicast issues, Server droping out of the cluster

If you are using weblogic cluster you need to make sure that you do not have any multicast issues. This is very significant If your application is using session replication or has

any distributed destination.

You can confirm that multicast traffic is working using simple multicast test using utility shipped with weblogic installation.

The MulticastTest utility helps you debug multicast problems when configuring a WebLogic Cluster. The utility sends out multicast packets and returns

information about how effectively multicast is working on your network.

Here is the syntax of multicastTest utility

java utils.MulticastTest -N name -A address

You need to run this test in each boxes with unique name identifier(-n) and a common multicast address. Make sure that multicast address used is unique in subnet and this should be

different from the one weblogic cluster is configured to use

Example.

For instance if you want to test multicast traffic between machine A and B

set the classpath using setDomainEnv.sh

$. ./setDomainEnv.sh (this is located under domain/bin)

run following command in Box A

$ java utils.MulticastTest -N serverA -A 237.155.155.1

Set up to send and receive on Multicast on Address 237.155.155.1 on port 7001

Will send a sequenced message under the name serverA every 2 seconds.

Received message 506 from serverA

Received message 533 from serverB

I (serverA) sent message num 507

Received message 507 from serverA

Received message 534 from serverB

I (serverA) sent message num 508

Received message 508 from serverA

Received message 535 from serverB

run following command in Box B once you set the classpath

$ java utils.MulticastTest -N serverB -A 237.155.155.1

If the multicast is traffic is working fine you can see the multicast messages being exchanged between these 2 nodes as shown above. You need to involve

your network system admistrator to investigate rootcause if the muticast traffic is not working.