Host down vs up

[Marc Powell]

> -----Original Message-----
> From: Joël Guened [mailto:joel at zonepro.fr]
> Sent: Friday, July 18, 2003 11:53 AM
> To: nagios-users at lists.sourceforge.net
> 
> Hi,
> 
> I have a difficulty to understand something.
> 
> When a service (eg. ftp) is down, the host is down too. And then, when a
> service comes UP, the host stay DOWN !
> 
> In my config file (hosts.cfg), I put check_command check-host-alive
> 
> How can I restore the process to up without restarting Nagios ?
> 
> Many servers have a firewall and can¹t be ping, Can be the reason ?

Yes, this is likely the reason for your difficulty. As detailed in several places in the documentation and FAQ's, Nagios does not check host status until a service on that host fails. It assumes the host is up if a service on that host is up. That is why the host *appears* up until a service failure forces a check, which would fail because it's behind the firewall. All seems well until the service recovers and nagios attempts to check the host again but it is _still_ unable to successfully check the host because of the firewall so you end up with a weird, but accurate as far as nagios is concerned, view of your host and it's services with the services up but the host down (unreachable in this case). Here are a few possible solutions, some better than others --

1) Change your check-host-alive command to something that does work through the firewall.
2) Allow ICMP ping through the firewall to your destination host from your monitoring host.
3) Change your check-host-alive command to check_dummy and have it always return OK.

--
Marc


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