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

[Ralph.Grothe at itdz-berlin.de]

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