void checkForDisallowedDefaults() {
    if (Boolean.getBoolean(GeodeGlossary.GEMFIRE_PREFIX + "disallowMcastDefaults")) {
      if (getMcastPort() != 0) { // it is not disabled
        if (getMcastAddress().equals(DistributionConfig.DEFAULT_MCAST_ADDRESS)
            && getMcastPort() == DistributionConfig.DEFAULT_MCAST_PORT) {
          throw new IllegalStateException(GeodeGlossary.GEMFIRE_PREFIX
              + "disallowMcastDefaults set and default address and port are being used");
        }
      }
    }
  }
For dunit tests we do not allow use of the default multicast address/port. Please use
AvailablePort.getRandomAvailablePort(AvailablePort.JGROUPS) to obtain a free port for your
test.
geode-core/src/main/java/org/apache/geode/distributed/internal/DistributionConfigImpl.java