[Nagiosplug-help] How to format send/expect strings for check_udp against SNMP managed devices?

[Tom Nail]

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Ralph,

Why not use the check_snmp plugin and check for a standard OID that is
supposed to be there, such as "SNMPv2-MIB::sysDescr.0". This confirms
that you have an SNMP agent up and responding on the port (your required
output). and leaves you free to work on more important things.

I mean, your wheel is undoubtedly shiny, but there's already one doing
this job.


Cheers,

- -=Tom Nail

Ralph.Grothe at itdz-berlin.de wrote:
> Hello,
> 
> I am struggling a bit with check_udp.
> 
> I wish to define a check command that can be run against a
> hostgroup snmp_hosts
> which should serve as a kind of check_icmp or check_host for all
> SNMP managed 
> devices which have a UDP listening socket at port 161.
> 
> This check should merely verify a willing to respond snmp agent 
> without querying any special OID(s) via e.g. check_snmp.
> I will assume for simplicity that only SNMPv1 is involved and
> that
> the checking manager can authenticate by a simple community
> string of "public".
> 
> Since UDP checks are a bit tricky I guess the check must coax the
> agent into
> sending a response PDU.
> Because I know next to nothing about the SNMP I looked at RFC1157
> to find out what the protocol requires minimally to be
> implemented.
> I also looked at a tcpdump in wireshark from my regular SNMP
> check of a known device
> to see that the used CPAN module adheres to the RFC.
> 
> So from what I saw in wireshark I naively tried this approach
> 
> 
> $ check_udp -v -H sensor_r01 -p 161 -E -s "version: version-1
> (0)\ncommunity: public" -e "version: version-1"
> Using service UDP
> Port: 161
> flags: 0x2
> Send string: version: version-1 (0)
> community: public
> server_expect_count: 1
>         0: version: version-1
> received 26 bytes from host
> #-raw-recv-------#
> 0
> #-raw-recv-------#
> looking for [version: version-1] anywhere in [0]
> couldn't find it
> UDP WARNING - Unexpected response from host/socket:
> 0|time=0.022995s;;;0.000000;10.000000
> 
> 
> Assuming that -m relates to the SNMP payload and thus only caring
> for the first 18 bytes of the response
> also doesn't work.
> 
> 
> $ check_udp -v -H sensor_r01 -p 161 -E -s "version: version-1
> (0)\ncommunity: public" -m 18 -e "version: version-1"
> Using service UDP
> Port: 161
> flags: 0x2
> Send string: version: version-1 (0)
> community: public
> server_expect_count: 1
>         0: version: version-1
> received 26 bytes from host
> #-raw-recv-------#
> 0
> #-raw-recv-------#
> looking for [version: version-1] anywhere in [0]
> couldn't find it
> UDP WARNING - Unexpected response from host/socket:
> 0|time=0.005487s;;;0.000000;10.000000
> 
> 
> 
> What do I need to change to get an OK from check_udp?
> 
> Regards
> 
> Ralph
> 
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