You need to send a message that the listening daemon will understand. The
check_snmp plugin speaks the SNMP language so it knows how to construct a
packet that snmpd will understand. I imagine an OID is a requirement for
check_snmp, as well as community string or security credentials, those are
all part of the "send". If you want to use check_udp for this, then you
have to construct that packet yourself.
On the flip-side, you should know the expected response to a known query.
If you make an SNMP request for .1.3.6.1.2.1.1.4.0 you should expect a
string from the "syscontact" line from your snmpd.conf in response.
Just like you would use check_http rather than check_tcp for an Apache
service, it's probably best to use a custom program like check_dns rather
than check_udp to check a DNS service. In the case of SNMP, I prefer to
use or write scripts that are specific to what I'm polling rather than
using a generic request/response program. For instance, a program like
check_snmp_load.pl could be alot more robust than running "check_snmp -o
.1.3.6.1.4.1.2021.10.1.3.1" alone.
-f
On Thu, 5 Sep 2013, Marco Borsani wrote:
> Date: Thu, 5 Sep 2013 09:06:38 +0200
> From: Marco Borsani
> Reply-To: Nagios Users List
> To: 'Andreas Ericsson' ,
> 'Nagios Users List'
> Subject: [Nagios-users] R: check_udp error message
>
> Ok, but what can I "send" and "receive" to/from the host?
>
> I also tried old version of check_udp (that does not need any string), but I
> read :
> No data was recieved from host!
> No response from host on port XX
>
> Or simply:
> No response from host on port XX
>
> I see another strange situation.
> On port 161 I can use check_snmp (work correctly), but if I use check_udp on
> port 161 it does not work at all !
> How can be possible ?
>
> Regards
>
> -Messaggio originale-
> Da: Andreas Ericsson [mailto:a...@op5.se]
> Inviato: marted? 3 settembre 2013 15:54
> A: Nagios Users List
> Cc: Marco Borsani
> Oggetto: Re: [Nagios-users] check_udp error message
>
> On 2013-09-03 12:33, Marco Borsani wrote:
>> Hi all
>>
>> I need to control many UDP ports.
>>
>>
>>
>> I run the command:
>>
>> ./check_udp ?H ?p 88
>>
>>
>>
>> I receive following error message (with state UNKNOWN) :
>>
>> With UDP checks, a send/expect string must be specified
>>
>>
>>
>> Can anyone help me to solve it?
>>
>> Those parameters should be optional..
>>
>
> UDP is a connection-less protocol. The "expect" string could indeed be
> optional, and we could just expect to get something at all back when we send
> something, but without sending anything we won't even touch the network, so
> the remote host has no idea that we're trying to talk to it and we won't
> know if the port is up.
>
> That's why "send", at least, is not optional.
>
>
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