SNMP Exporter

SNMP is one of the most prevalent (and clunky) protocols still widely used on network-attached devices. But it’s a good general-purpose way to get data from lots of different makes of products in a similar way.

But Prometheus doesn’t understand SNMP. The solution is a translation service that acts a a middle-man and ’exports’ data from those devices in a way Prometheus can.

Installation

Assuming you’ve already installed Prometheus, install some SNMP tools and the exporter. If you have an error installing the mibs-downloader, check troubleshooting at the bottom.

sudo apt install snmp snmp-mibs-downloader
sudo apt install -t testing prometheus-snmp-exporter

Change the SNMP tools config file to allow use of installed MIBs.

sudo sed -i 's/^mibs/# &/' /etc/snmp/snmp.conf

Preparation

We need a target, so assuming you have a switch somewhere and can enable SNMP on it, let’s query the switch for its name, AKA sysName. Here we’re using version “2c” of the protocol with the read-only password “public”. Pretty standard.

# Note: app
snmpwalk -v 2c -c public some.switch.address sysName

SNMPv2-MIB::sysName.0 = STRING: Some-Switch

Note: If you get back an error or just the ‘iso’ prefixed value, double check your MIBs are installed.

Configuration

To add this switch to the Prometheus scraper, add a new job to the prometheus.yaml file. This job will include the targets as normal, but also the path (since it’s different than default) and an optional parameter called module that specific to the SNMP exporter. It also does something confusing - a relabel_config

This is because Prometheus isn’t actually taking to the switch, it’s talking to the local SNMP exporter service. So we put all the targets normally, and then at the bottom ‘oh, by the way, do a switcheroo’. This allows Prometheus to display all the data normally with no one the wiser.

...
...
scrape_configs:
  - job_name: 'snmp'
    static_configs:
      - targets:
        - some.switch.address    
    metrics_path: /snmp
    params:
      module: [if_mib]
    relabel_configs:
      - source_labels: [__address__]
        target_label: __param_target
      - source_labels: [__param_target]
        target_label: instance
      - target_label: __address__
        replacement: 127.0.0.1:9116  # The SNMP exporter's real hostname:port.

Operation

No configuration on the exporter side is needed. Reload the config and check the target list. Then examine data in the graph section. Add additional targets as needed and the exporter will pull in the data.

http://some.server:9090/classic/targets

These metrics are considered well known and so will appear in the database named sysUpTime and upsBasicBatteryStatus and not be prefixed with snmp_ like you might expect.

Next Steps

If you have something non-standard, or you simply don’t want that huge amount of data in your system, look at the link below to customize the SNMP collection with the Generator.

SNMP Exporter Generator Customization

Troubleshooting

The snmp-mibs-downloader is just a handy way to download a bunch of default MIBs so when you use the tools, all the cryptic numbers, like “1.3.6.1.2.1.17.4.3.1” are translated into pleasant names.

If you can’t find the mibs-downloader its probably because it’s in the non-free repo and that’s not enabled by default. Change your apt sources file like so

sudo vi /etc/apt/sources.list

deb http://deb.debian.org/debian/ bullseye main contrib non-free
deb-src http://deb.debian.org/debian/ bullseye main contrib non-free

deb http://security.debian.org/debian-security bullseye-security main contrib non-free
deb-src http://security.debian.org/debian-security bullseye-security main contrib non-free

deb http://deb.debian.org/debian/ bullseye-updates main contrib non-free
deb-src http://deb.debian.org/debian/ bullseye-updates main contrib non-free

It may be that you only need to change one line.