Problems connecting remotely to a RAC DB via sqlplus
Remote SYSDBA login uses password file authentication. A 11g RAC database uses local password files on each node in the local filesystem ($ORACLE_HOME/dbs). When you grant SYSDBA to a user, or change the password of this user, the password file is automatically updated on the node where the command was executed, but not on the other nodes. You need to manually copy the updated password file to the other nodes as well, otherwise you will not be able to log in to the other nodes.

Starting with 12c, the database password file can be stored in ASM, and it is not needed to perform such manual maintenance steps anymore.