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Nagios, 2nd Edition by Wolfgang Barth

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10.6 Indirect Checks

NRPE executes not just local plugins, but any plugins that are available. If you use network plugins via NRPE, these are referred to as indirect checks, as illustrated graphically in Figure 10-1.

Indirect checks with NRPE

Figure 10-1. Indirect checks with NRPE

If every network service was tested directly across the firewall, it would have to open all the required ports. In the example, these would be the ports for SMTP, HTTP, LDAP, PostgreSQL, and SSH. If the checks are performed indirectly from a computer that is behind the firewall, on the other hand, then it is sufficient just to have the port for NRPE (TCP port 5666) open on the firewall. As long as ...

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