I faced this issue when trying to run multiple Hadoop MR2 instances on the same node. The default value for this property is hardcoded in the ShuffleHandler.java class so it results in port conflicts. The issue is resolved if you set the property value in your conf files. But the absence of this property from *-default.xml files is confusing. So It'll be cleaner to move this property to mapred-default.xml, so its default value can be easily identified and changed if needed.