Since all the server instances to be monitored are on the same machine, you must change the default SNMP adapter ports for the server instances to avoid port conflicts. Use the following asadmin commands.
asadmin set standalone-instance1.property.snmp-adapter-port=10162 asadmin set clustered-instance1.property.snmp-adapter-port=10163 asadmin set clustered-instance2.property.snmp-adapter-port=10164
If the server instances are already running, you must restart them for these port changes to take effect. For more information about changing the SNMP adapter ports, see the Sun GlassFish Enterprise Manager SNMP Monitoring 1.0 Installation and Quick Start Guide.