The tnsnames.ora file is located in ORACLE_HOME\network\admin. In an Oracle Database 11g Release 2 instance running ASM or RAC, the tnsnames.ora file is read by default from the grid infrastructure home directory at Grid_home\network\admin.
If you are using an Oracle Database 11g Release 2 instance running ASM or RAC, set the Replication Agent asm_tns_filename parameter to Grid_home\network\admin\tnsnames.ora.
By default, the tnsnames.ora file at Grid_home\network\admin contains an incomplete ASM entry that lacks information in the DESCRIPTION and SERVICE_NAME fields. If you are using an Oracle Database 11g Release 2 instance running ASM, set the Replication Agent asm_tns_connection parameter to the ASM connection name specified in this incomplete ASM entry. Replication Agent completes the DESCRIPTION and SERVICE_NAME fields, and you can then use the tnsnames.ora file in Grid_home\network\admin to connect to the ASM instance server.