By Default Oracle ASM don’t allow remote sysdba connection since ASM instance is in NOMOUNT state. You Might get ORA-12528: TNS:listener: all appropriate instances are blocking new connections error when you are trying to connect ASM instance remotely. To bypass this error you need to add UR=A in the tns files like example below and connect as sysdba:
ASM =
(DESCRIPTION =
(ADDRESS = (PROTOCOL = TCP)(HOST = xxxxx)(PORT = 1521))
(CONNECT_DATA =
(SERVER = DEDICATED)
(SERVICE_NAME = +ASM)
(UR =A)
)
)