Chapter 15. Troubleshooting and Monitoring

In this chapter we will learn how to use tools to debug and monitor VPN tunnels. We will also learn how to scan and test the connectivity of a (VPN) server with standard Linux command-line tools. In the second part we will deal with the following graphical monitoring tools:

  • Ntop
  • Munin
  • Nagios
  • OpenVPNgraph

Testing network connectivity

In our typical OpenVPN setup, we have connected two networks ( and through two Linux servers that are connected to the Internet through a default gateway. Between the two Linux servers is a tunnel that uses virtual interfaces with the IPs and

In the connected local networks there are two Linux machines that we will use to ...

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