How to externally monitor the operation of the Internet connection without an external IP?

Question

Computer networks

There is a small company that is connected to the Internet without using a white external address. You need to somehow monitor the availability of the Internet connection from the outside in order to find out about the disconnection immediately, and not by calling the phone. Outside there is a Nagios server, mb, there is a plugin for such a task. Or some other solution.

Answer 1

Ping some monitoring thread from outside, which will raise an alarm if a ping does not come at the right time.
You can set up your monitoring on any VPS or look for ready-made services (a similar question ran through the toaster recently). If you have Nagios outside, then you can write a script yourself that will periodically send him a simple "ok", and on Nagios already set up after how many minutes of no response to raise an alarm.

Answer 2

write a script that, for example, will send certain packets to an external server.
for example send packets
echo 12323123 | netcat 127.0.0.1 15666
and the server to listen
netcat -l 15666
When a packet is received, the listening ends and the received line is displayed.
If there were no packets for a long time, then display a message

Answer 3

There was a similar issue. Zabbix in an organization without an external IP using web verification sent messages that were received by a script running on a free hosting. If messages were not received for a long time, alerts were sent.