General tcp_check question

[Jakob Curdes]

>
> CRITICAL - Socket timeout after 60 seconds
>  I suspect that it is an firewall issue at that site so I wanted to 
> know that what is underlying command of tcp_check and how can I allow 
> or disallow tcp_check command to run on my system if I am the system 
> administrator on that system.
Well, unfortaunately it is not so easy. If you get a timeout this just 
means that in the 60 seconds nothing came back. Probably there is some 
network obstacle in between, but we occasionally observe that also with 
loaded servers that just take longer to respond. The fact that nothing 
came back tells you just that - it is hard to conclude WHY nothing came 
back.

What nagios does is essentially

telnet host portnumber

You can do this by hand, e.g. telnet site2 9002 - if you get a repsonse 
at all (empty window), you have a connection to that port. If telnet 
hangs for a long time and then closes, you have the case that nagios 
sees: nothing comes back and after some time you get a network timeout. 
If it closes immediately this probably means that nothing is listening 
at that port; although even this answer can come from a firewall.

HTH.,

Jakob Curdes

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