I think you have two problems:
1. Your local (client) tnsnames.ora thinks that PIPPO is running on your local machine (host = 127.0.0.1 means localhost). So you need to specify the host where the database (and listener) reside.
2. You're doing this over a firewall. You have a listener running on port 1521 but are using 1551 in your tnsnames.ora.
If you have other Oracle clients on the non-trusted network then maybe you just need to fix the hostname. If that doesn't work, then you've a more challenging problem.
If you have control over your client's network location in respect to the firewall, then put it on the server (secure) side of the firewall, change your hostname, and change the port to 1521.
This will test your Oracle-side configuration, without the complication of your firewall. Once you get tnsping to work from there, move your client back to the non-secure side.
You may need to update your port back to 1551, but there's not enough information on your post to comment about firewall, port-forwarding, port-tunneling, or anything else along these lines.