SNMP Tools

To configure Zenoss to monitor a device using SNMP, it is necessary to understand a bit about SNMP and the specific capabilities of your device. This section will walk you through using Net-SNMP, smidump, and snmpsim to learn about SNMP and your device.

Installing Net-SNMP

In the SNMP world the client is referred to as a manager and the server is referred to as the agent. Net-SNMP is software that provides both an agent that’s used in all sorts of devices, and many command line tools that act as manager. We’re only going to need the command line tools, so we’ll be installing the net-snmp-utils package.

You can install Net-SNMP’s command line tools by running the following command as root.

yum -y install net-snmp-utils

Installing libsmi

smidump is a useful command line tool for converting MIBs to other formats. We’ll be using it later in this tutorial to research what a MIB provides.

Install smidump by installing the libsmi package with the following command.

yum -y install libsmi

Installing the SNMP Simulator

When developing a ZenPack to monitor an SNMP-enabled device it can often be useful to simulate the device’s SNMP agent. There are many tools available to do this. For this guide we will be using the free snmpsim because it’s easy to install on our Zenoss host.

  1. Run the following commands as root to install snmpsim:

    yum -y groupinstall "Development Tools"
    yum -y install python-devel
    easy_install snmpsim
    mkdir -p /usr/share/snmpsim/data
    mkdir -p /var/run/snmpsim
    useradd -U snmpsim
    chown snmpsim:snmpsim /var/run/snmpsim
    
  2. Run the following command as root to install a NetBotz recording.

    wget https://goo.gl/OJe2vL -O /usr/share/snmpsim/data/public.snmprec
    
  3. Run the following command as root to run snmpsim.

    snmpsimd.py \
      --process-user=snmpsim \
      --process-group=snmpsim \
      --agent-udpv4-endpoint=172.17.42.1:161 \
      --daemonize
    
  4. Test the simulator with the following snmpwalk command.

    snmpwalk -v2c -c public 172.17.42.1 sysDescr
    

    You should see the following output.

    SNMPv2-MIB::sysDescr.0 = STRING: Linux Netbotz01 2.4.26 #1 Wed Oct 31 18:09:53 CDT 2007 ppc
    

Using snmpwalk

The tool you’ll be using most often is called snmpwalk. All SNMP values are arranged on a tree, and snmpwalk allows you to query for all data under a given branch of that tree. See the following example that walks all values under the system branch.

Run the snmpwalk command.

snmpwalk -v2c -c public 172.17.42.1 system
SNMPv2-MIB::sysDescr.0 = STRING: Linux Netbotz01 2.4.26 #1 Wed Oct 31 18:09:53 CDT 2007 ppc
SNMPv2-MIB::sysObjectID.0 = OID: SNMPv2-SMI::enterprises.5528.100.20.10.2006
DISMAN-EVENT-MIB::sysUpTimeInstance = Timeticks: (7275488) 20:12:34.88
SNMPv2-MIB::sysContact.0 = STRING: unknown
SNMPv2-MIB::sysName.0 = STRING: Netbotz01
SNMPv2-MIB::sysLocation.0 = STRING: Z1 Rack02 NetBotz01

We can see that this NetBotz device seems to be based on Linux and that we have some more-or-less useful information about the device’s name, location and administrative contact.

The second line with the sysObjectID has an unusual value. It’s a partially decoded OID. It isn’t decoded enough for us to know what it means. SNMP tools including Net-SNMP use MIB files to decode these OIDs into human readable values. In fact, we’re only able to read most of the output above because Net- SNMP has a set of standard MIBs enabled by default.

Let’s run that command again, but use the -On flag to tell snmpwalk not to decode OIDs.

snmpwalk -v2c -c public -On 172.17.42.1 system
.1.3.6.1.2.1.1.1.0 = STRING: Linux Netbotz01 2.4.26 #1 Wed Oct 31 18:09:53 CDT 2007 ppc
.1.3.6.1.2.1.1.2.0 = OID: .1.3.6.1.4.1.5528.100.20.10.2006
.1.3.6.1.2.1.1.3.0 = Timeticks: (7275488) 20:12:34.88
.1.3.6.1.2.1.1.4.0 = STRING: unknown
.1.3.6.1.2.1.1.5.0 = STRING: Netbotz01
.1.3.6.1.2.1.1.6.0 = STRING: Z1 Rack02 NetBotz01

While this data is mostly less valuable than the decoded version above, it’s more useful for a single reason. We can take that .1.3.6.1.4.1.5528.100.20.10.2006 value and search the Internet for it. It’s best to remove the leading . and search for 1.3.6.1.4.1.5528.100.20.10.2006 instead. This should lead you to the NETBOTZV2-MIB which will contain the decoding information we need to learn more about this device.

Run the following command to download NETBOTZV2-MIB.mib into /usr/share/snmp/mibs/.

wget https://goo.gl/0v4Kti -O /usr/share/snmp/mibs/NETBOTZV2-MIB.mib

Now we can run the original snmpwalk command again with the addition of the -m all option. This option tells Net-SNMP tools to use all MIBs.

snmpwalk -v2c -c public -m all 172.17.42.1 system
SNMPv2-MIB::sysDescr.0 = STRING: Linux Netbotz01 2.4.26 #1 Wed Oct 31 18:09:53 CDT 2007 ppc
SNMPv2-MIB::sysObjectID.0 = OID: NETBOTZV2-MIB::netBotz420ERack
DISMAN-EVENT-MIB::sysUpTimeInstance = Timeticks: (7275488) 20:12:34.88
SNMPv2-MIB::sysContact.0 = STRING: unknown
SNMPv2-MIB::sysName.0 = STRING: Netbotz01
SNMPv2-MIB::sysLocation.0 = STRING: Z1 Rack02 NetBotz01

Now we can see that the sysObjectID is NETBOTZV2-MIB::netBotz420ERack. This gives us a better idea of exactly what kind of device it is. We’ll see that as we look deeper into this device that the NETBOTZV2-MIB will prove more useful.

Default Net-SNMP Options

The snmpwalk usage showed three primary command line options that we tend to use most of the time. Net-SNMP allows you to specify these in a configuration file so you don’t have to type them every time. I recommend doing this.

Create /etc/snmp/snmp.conf and add the following lines.

defVersion v2c
defCommunity public
mibs ALL

These lines add the following equivalent command line options respectively:

  • -v2c
  • -c public
  • -m all

So now we can run this command.

snmpwalk 172.17.42.1 sysObjectID

And get the same results as if we ran.

snmpwalk -v2c -c public -m all 172.17.42.1 sysObjectID

This will save you time while developing this ZenPack, and others in the future.

Decoding and Encoding OIDs

Often it can be useful to turn numeric OIDs into their human-readable equivalent, or vice-versa. The snmptranslate command can be used for this. See the following examples.

OID to name:

# snmptranslate .1.3.6.1.4.1.5528.100.20.10.2006
NETBOTZV2-MIB::netBotz420ERack

Name to OID:

# snmptranslate -On NETBOTZV2-MIB::netBotz420ERack
.1.3.6.1.4.1.5528.100.20.10.2006