Information:
Oracle Listener runs on database server to receive the incoming connection request and provide the connectivity with database server.
Listener can be configured on multiple listening address and its configuration can be stored in listener.ora
The default listener configuration with name LISTENER and listen on TCP/IP port 1521.
(ADDRESS=(PROTOCOL=TCP)(HOST=hostname)(PORT=1521))
It can be configured in two ways statically and dynamically. Statically registration can be done in listener.ora file where as dynamic registration is called service registration. This dynamic registration has been performed by PMON process.
SERVER=
(DESCRIPTION=
(ADDRESS_LIST=
(ADDRESS=(PROTOCOL=tcp)(HOST=doping)(PORT=1521))
(ADDRESS=(PROTOCOL=ipc)(KEY=extproc) (queuesize=100))))
SID_LIST_LISTENER=
(SID_LIST=
(SID_DESC=
(SID_NAME=KS1)
(ORACLE_HOME=/usr/oracle/12202)
(PROGRAM=extproc)))
This example shows that the listener is registered with name SERVER in listener.ora
