Oracle: DBA_DB_LINK_SOURCES

select
   dls.source_id,
   dls.username,          -- Name of user who logged into the local database (corresponds to `username` in `v$session`)
   dls.db_name,
   dls.first_logon_time,
   dls.last_logon_time,
   dls.logon_count,
   dls.dbid,
   dls.db_unique_name,
   dls.host_name,
   dls.ip_address,
   dls.protocol,        -- ipc, sdp, tcp, tcps or NULL.
   dls.user#
from
   dba_db_link_sources dls;