SQL*Plus connection SetUp: ORA-12154 Error - oracle

Question

Sorry for the noob question but I am new to Oracle SQL software.
I've been trying to create a connection to my database student (created on SQL Developer), but got quite confusing since I'm using a client-computer which will connect to server.
Below are the info about the connection:
Connection Name: LARGER123
Username: LARGER123
Hostname: uxkg265.admin.plent
Port: 1520
SID: ticp5076
Client-computer username: r5678
When I open the SQL Plus prompt, I tried several combinations on the username in order to establish the connection, but got the same error ORA-12154 Error.
I though that it could be the way I was setting the things on username field, so I followed the instructions from Oracle's website:
https://docs.oracle.com/database/121/ADMQS/GUID-1A15D322-B3AC-426A-86A1-EB7590930687.htm#ADMQS045
Basically it tells to "build" the username structure in that way:
nick#"dbhost.example.com/orcl.example.com"
Where: "nick" is the user; "dbhost.example.com" is the host; and "orcl.example.com" is the database.
So, following the example I put my username in that way and got errors:
LARGER123#"uxkg265.admin.plent/student"
I tried different ways, including the Port and SID but got no success.
Do you have a better idea of what's my mistake?

Answer 1

Are you quite certain somebody is listening where you are trying to connect. I would suggest you start by testing with telnet.
You say your server has the domain name “uxkg265.admin.plent”
nslookup uxkg265.admin.plent
I just checked my IP address and found:
$ nslookup $(hostname)
Server: xxx.xxx.xxx.xxx
Address: xxx.xxx.xxx.xx##53
Name: mydomain.myorg.com
Address: 192.168.56.1
I just tried to connect to my oracle instance and got:
$ telnet 192.168.56.1 1521
Trying 192.168.56.1...
Connected to 192.168.56.1
Escape character is '^]'.
^]
telnet> quit
Connection closed.
If I try to the wrong port, I get:
$ telnet 192.168.56.1 1522
Trying 192.168.56.1...
telnet: connect to address 192.168.56.1: Connection refused
I was able to connect with:
sqlplus myoracle/testpass#192.168.56.1:1521/UPGR
where UPGR is the service name.
I was also able to connect with:
sqlplus myoracle/testpass#"(DESCRIPTION=(ADDRESS=(PROTOCOL=TCP)(HOST=192.168.56.1)(PORT=1521))(CONNECT_DATA=(SID=UPGR)))"
With UPGR as the SID.
I had some trouble initially because my version of Oracle Linux had iptables enabled and that was keeping me from connecting using sqlplus. As soon as I disabled this protection, I was able to use Oracle.
sudo service iptables stop
sudo chkconfig iptables off
(Keep in mind that iptables serves a purpose. For my test system running on my PC in VirtualBox, turning it off is fine. For other systems, maybe not.)

Answer 2

ORA-12154 is TNS:could not resolve the connect identifier specified, but you likely aren't using TNS to resolve the connect identifier: have you edited the tnsnames.ora file on the client machine and created an entry for the SID you're trying to connect to? Probably not.
Instead of selecting SID, select "Service name" and put the Oracle SID there. With the "Basic" connection type, that should use the host/port and service name explicitly to build the connection rather than relying on TNS to look up (resolve) the SID.