Oracle 12c network connection issue - oracle

I face the below error when i try to connect to the database

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dbeaver connect TNS:destination host unreachable ca

Can connect to oracle database from Oracle SQL developer but cannot connect to sys as sysdb from command prompt
I wanted to connect to oracle database using dbeaver. Facing an error

While connecting to Oracle 12c DB facing error ORA-12543: TNS : destination host unreachable

I am able to connect to Oracle12C DB with with Oracle SQL Developer. but not able to connect with SQL Plus. with same credentials.
Why this is happening ?

UDL connection with Oracle database using OLEDB Provider

I am trying to connect the oracle database using universal data link(UDL) with the provider as "Oracle provider for OLEDB"
The test connection fails with the below error
Test connection failed because of an error in initializing provider. ORA-12170: TNS:Connect timeout occurred
I am able to connect to the oracle database using SQLPLUS and Oracle SQL Developer from the same machine.
Please suggest the possible root cause of the issue.

Unable to connect to the Oracle 19c from a client

I'm using Oracle 19c. I have tested the connection by the commands "ping [ip]" and "tnsping", and both were successfully connected. Now, I want to connect to the Oracle developer from a client, and it is not be able to connect.
When I was using Oracle 12c, there was no such a problem. I really don't know what's going wrong here.

Error while connecting to Oracle database from oracle SQL Developer though I've the oracle client installed

I've installed Oracle client in my machine, when I'm trying to connect to the oracle database server from Oracle SQL Developer am getting the following error:
Status : Failure -Test failed: IO Error: The Network Adapter could not establish the connection
But am able to connect to the server using sql plus and TOAD as well from my machine. What is the issue if Toad connects to the server why cant my Oracle sql developer could not connect??
checked all the possible solutions like:
tns strings checking, telnet to the server and its port,
changing the oracle home in the sqldeveloper->tools->preferences->database->advanced tab.
None solved my issue. Is this the firewall issue?
If it is so how am able to connect using TOAD/sql plus ??
UPDATE: I'm connecting to the Oracle database server using the VPN.
Any help is much appreciated.
Thanks in advance.

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