Jira is not able to a database server

[Rajesh]

I have installed the Jira and it was working fine but all of a sudden it was not able to connect with the database, so I have tried to uninstall and re-install it back.
But the installation fails with the same below error as "not able to connect with the database". The database server is up and running and I tried to install the Jira on the server where database is running.
Please help me to solve this issue.

[Suhas P]

Check if the you can reach to Database server from application server by ping. 

Also Check the IP tables entries if it allows the traffic from database server.

[Vasiliy Zverev]

In my case this usually happends because of firewall settings or proxy filters.