Am 22.10.2012 15:02, schrieb Leonardo Bacha Abrantes:
Hello,
I know that is possible to use another plugin to check if host is up,
however, I never did it on old version of nagios.
now I'm using nmap, and it's working.
http://systhread.net/texts/2010q3nmap_ping.php
It depends on the firewall if this solution works. NMAP tries ICMP and
if that does not work it sends a "probe" TCP packet to an arbitrary port
of the host, if it gets back anything (e.g. the host responds with RST-
no service on this port), nmap sees the host as "up". If you have a
firewall that is acutally dropping incoming packets (and not sending
back a RST/SYN/ACK), then also this technique will fail in a similar
manner as the ICMP ping. A Firewall might also ALWAYS send an RST packet
for a certain port, so nmap would assume that the host is up while it
was the firewall that sent the answer.
So, in short: it is very difficult to determine the actual status of a
host behind an arbitrary firewall/using packets sent from the monitoring
server/; in this case it is much safer to use passive checks (i.e.
sending results from the host side).
jc
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