Re: managing Devices that don't allow SNMP Queries

Now, that's an interesting issue, just my thing! Assuming you have a way 
of gatering data (as you indicate) using a script, you can make that 
data snmp readable using snmpd and the "pass" or "pass_persist" feature.

What you need to do:

1 - Edit /etc/snmp/snmpd.conf and add the following line:

pass .1.3.6.1.3.x /path/script.php

Adjust the x and the script/program to suit your needs. the x can be any 
number, since .1.3.6.1.3 is the SNMP experimental tree free for you to 
use much like RFC 1918 IP addresses (10.0.0.0/8, 172.16.0.0/12 and 
192.168.0.0/16). I used my phone number as x in a project:)

While you're there, set up an SNMP community that can be used to read 
your new private tree:

rocommunity public 0.0.0.0/0
(more lines may be needed depending on config and version)

2 - Write a program/script to serve OID values. The script should take 
two arguments. The first is query type and the second the requested OID.

Query type is -g for get and -n for get next so basically the script 
could be run manually like this:

# script.php -g .1.3.6.1.3.12345.1.0
.1.3.6.1.3.12345.1.0
integer
0

So, the output NEEDS to be:
OID (with leading dot...)
type
value

Not that hard to accomplish as long as your data can be processed by the 
script. I have used a MySQL database to store the data gathered and then 
used that dB to read values using the PHP script.


If you need read performance exceeding more than a few snmpreads per 
second you need to consider the "pass_persist" feature. We can do 8 
reads per second with the "pass" script, and spawning the new process 
for each read is probably what takes so much time. I originally 
implemented it for a low-rate reading application, but then "they" kept 
increasing the demands on read performance... Surely there are lots of 
examples out there with pass_persist.


How will you be reading data from your device? Telnet/SSH/HTTP/...? 
"expect" is a function we all "love to hate" with its TCL syntax, but 
very usable for automatically telnetting/SSHing into a switch or 
whatever and do things automagically. After getting the data, putting it 
in a database or file in a structured way readable by the "pass" script 
is the next task for you, but then, you're done! I even monitor a Dell 
server using the "ipmitool" program from Dell that is supposed to be 
interactive, but "expect" does the interactivity for me once evey minute...


pass_persist:
http://www.net-snmp.org/wiki/index.php/Tut:Extending_snmpd_using_shell_scripts

Expect:
http://www2.tcl.tk/11583

/Fredrik


Craig Taylor skrev 2014-04-03 17:30:
>
> I want to proactively monitor a small storage system with Net SNMP, 
> but the storage doesn't allow querying with snmpget commands.  Can I 
> create an external script to get the string another way and pass that 
> string onto the tool like it came from an snmpget command?
>
> If yes, any help on how to do this would be appreciated.
>
> Thanks,
>
> Craig D. Taylor
> m: 630.485.9975
> e:  [email protected]
>
>
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