EZCONNECT and HOSTNAME resolution methods

EZCONNECT is the easy connect protocol, available in 10g, whenever you want to connect to a database without tnsnames and without ldap.

$ grep -iw directory_path $TNS_ADMIN/sqlnet.ora
names.directory_path=EZCONNECT
$ sqlplus scott/tiger@//srv01:1521/db01

connect to server srv01 on port 1521 for service db01

HOSTNAME was the old-fashion way to connect to a database, where hostname = sid and port = 1521. In this regard EZCONNECT is just an extension of the hostname method.

Typical HOSTNAME usage, that is the same as EZCONNECT with default port 1521.
sqlplus scott/tiger@db01
connect to server db01 on port 1521 for service db01

There is a behavior change between 10g and 11g. In 10g, the default service name defaulted to the DNS alias used to connect. In 11g, the default is null.

$ nslookup db01
Server:  ns001.example.com
Address:  198.0.0.30

Name:    srv01.example.com
Address:  198.0.0.60
Aliases:  db01.example.com

$ nslookup db02
Server:  ns001.example.com
Address:  198.0.0.30

Name:    srv01.example.com
Address:  198.0.0.60
Aliases:  db02.example.com

Both DB01 and DB02 DNS aliases point to the same server.

Let’s try with 10g

$ sqlplus -L scott/tiger@db01.example.com

SQL*Plus: Release 10.2.0.3.0 - Production on Mon Feb 7 15:46:53 2011

Copyright (c) 1982, 2006, Oracle.  All Rights Reserved.

Connected to:
Oracle Database 10g Enterprise Edition Release 10.2.0.4.0 - 64bit Production
With the Partitioning, OLAP, Data Mining and Real Application Testing options

SQL> select global_name from global_name;
GLOBAL_NAME
---------------------------------------
DB01.EXAMPLE.COM
SQL> quit
$ sqlplus -L scott/tiger@db02.example.com

SQL*Plus: Release 10.2.0.3.0 - Production on Mon Feb 7 15:47:33 2011

Copyright (c) 1982, 2006, Oracle.  All Rights Reserved.

Connected to:
Oracle Database 10g Enterprise Edition Release 10.2.0.4.0 - 64bit Production
With the Partitioning, OLAP, Data Mining and Real Application Testing options

SQL> select global_name from global_name;
GLOBAL_NAME
---------------------------------------
DB02.EXAMPLE.COM

Let’s try with 11g sqlplus

$ sqlplus -L scott/tiger@db01.example.com

SQL*Plus: Release 11.2.0.2.0 Production on Mon Feb 7 15:50:27 2011

Copyright (c) 1982, 2010, Oracle.  All rights reserved.

ERROR:
ORA-12504: TNS:listener was not given the SERVICE_NAME in CONNECT_DATA

SP2-0751: Unable to connect to Oracle.  Exiting SQL*Plus

It no longer works. Period. This is documented as Problem 556996.1 in Metalink.

A 10g tnsping will reveal

$ tnsping db01.example.com:1521

TNS Ping Utility for IBM/AIX RISC System/6000: Version 10.2.0.3.0 - Production on 07-FEB-2011 15:52:34

Copyright (c) 1997, 2006, Oracle.  All rights reserved.

Used parameter files:
/home/lsc/sqlnet.ora

Used HOSTNAME adapter to resolve the alias
Attempting to contact (DESCRIPTION=(CONNECT_DATA=(SERVICE_NAME=db01.example.com))(ADDRESS=(PROTOCOL=TCP)(HOST=198.0.0.60)(PORT=1521)))
OK (80 msec)

In 10g the service_name is the connection dns alias used

In contrary, the 11g tnsping service name is null

$ tnsping db01.example.com:1521

TNS Ping Utility for IBM/AIX RISC System/6000: Version 11.2.0.2.0 - Production on 07-FEB-2011 15:56:55

Copyright (c) 1997, 2010, Oracle.  All rights reserved.

Used parameter files:
/home/lsc/sqlnet.ora

Used HOSTNAME adapter to resolve the alias
Attempting to contact (DESCRIPTION=(CONNECT_DATA=(SERVICE_NAME=))(ADDRESS=(PROTOCOL=TCP)(HOST=198.0.0.60)(PORT=1521)))
OK (10 msec)

The tnsping works, but the service_name is empty.

How to fix this?

1) you specify the SID in easy connect (yes, this is easy!)

$ tnsping db01.example.com:1521/db01.example.com

TNS Ping Utility for IBM/AIX RISC System/6000: Version 11.2.0.2.0 - Production on 07-FEB-2011 15:59:10

Copyright (c) 1997, 2010, Oracle.  All rights reserved.

Used parameter files:
/home/lsc/sqlnet.ora

Used HOSTNAME adapter to resolve the alias
Attempting to contact (DESCRIPTION=(CONNECT_DATA=(SERVICE_NAME=db01.example.com))(ADDRESS=(PROTOCOL=TCP)(HOST=198.0.0.60)(PORT=1521)))
OK (10 msec)

2) you use 10g, or 10g behavior in 11g with patch 9271246 (available only on a limited number of plateforms, os and db versions),

3) you specify a default service for your listener

$ vi listener.ora
DEFAULT_SERVER_LISTENER=DB01
$ lsnrctl reload
$ sqlplus -L scott/tiger@db01 

Copyright (c) 1982, 2010, Oracle.  All rights reserved.

Connected to:
Oracle Database 10g Enterprise Edition Release 10.2.0.4.0 - 64bit Production
With the Partitioning, OLAP, Data Mining and Real Application Testing options

SQL> 

This is a bit confusing as if you are servicing more than one database per listener, all dns aliases will default to the same database. So I would not recommend a default service name if there is more than one service name.

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