<html> <head> <meta content="text/html; charset=ISO-8859-1" http-equiv="Content-Type"> </head> <body bgcolor="#FFFFFF" text="#000000"> <div class="moz-cite-prefix">Am 22.10.2012 15:02, schrieb Leonardo Bacha Abrantes: </div> <blockquote cite="mid:CAG+8EEYKtbFaBwRen+18G_eY-Y0g_8tEWaQ-j-U3cL+25oe7RA@mail.gmail.com" type="cite">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. <a moz-do-not-send="true" href="http://systhread.net/texts/2010q3nmap_ping.php">http://systhread.net/texts/2010q3nmap_ping.php</a> </blockquote> 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 </body> </html>