nicolascanceill-optiver / snmp_exporter

SNMP Exporter for Prometheus

Prometheus SNMP Exporter

This exporter is the recommended way to expose SNMP data in a format which Prometheus can ingest.

To simply get started, it's recommended to use the if_mib module with switches, access points, or routers.

Concepts

While SNMP uses a hierarchical data structure and Prometheus uses an n-dimnensional matrix, the two systems map perfectly, and without the need to walk through data by hand. snmp_exporter maps the data for you.

Prometheus

Prometheus is able to map SNMP index instances to labels. For example, the ifEntry specifies an INDEX of ifIndex. This becomes the ifIndex label in Prometheus.

If an SNMP entry has multiple index values, each value is mapped to a separate Prometheus label.

SNMP

SNMP is structured in OID trees, described by MIBs. OID subtrees have the same order across different locations in the tree. The order under 1.3.6.1.2.1.2.2.1.1 (ifIndex) is the same as in 1.3.6.1.2.1.2.2.1.2 (ifDescr), 1.3.6.1.2.1.31.1.1.1.10 (ifHCOutOctets), etc. The numbers are OIDs, the names in parentheses are the names from a MIB, in this case IF-MIB.

Mapping

Given a device with an interface at number 2, a partial snmpwalk return looks like:

1.3.6.1.2.1.2.2.1.1.2 = INTEGER: 2         # ifIndex for '2' is literally just '2'
1.3.6.1.2.1.2.2.1.2.2 = STRING: "eth0"     # ifDescr
1.3.6.1.2.1.31.1.1.1.1 = STRING: "eth0"    # IfName
1.3.6.1.2.1.31.1.1.1.10.2 = INTEGER: 1000  # ifHCOutOctets, 1000 bytes
1.3.6.1.2.1.31.1.1.1.18.2 = STRING: ""     # ifAlias

snmp_exporter combines all of this data into:

ifHCOutOctets{ifAlias="",ifDescr="eth0",ifIndex="2",ifName="eth0"} 1000

Scaling

A single instance of snmp_exporter can be run for thousands of devices.

Usage

Installation

Binaries can be downloaded from the Github releases page and need no special installation.

We also provide a sample systemd unit file.

Running

Start snmp_exporter as a daemon or from CLI:

./snmp_exporter

Visit http://localhost:9116/snmp?module=if_mib&target=1.2.3.4 where 1.2.3.4 is the IP or FQDN of the SNMP device to get metrics from and if_mib is the default module, defined in snmp.yml.

Configuration

The default configuration file name is snmp.yml and should not be edited by hand. If you need to change it, see Generating configuration.

The default snmp.yml covers a variety of common hardware walking them using SNMP v2 GETBULK.

Prometheus Configuration

target and module can be passed as a parameter through relabelling.

Example config:

scrape_configs:
  - job_name: 'snmp'
    static_configs:
      - targets:
        - 192.168.1.2  # SNMP device.
        - switch.local # SNMP device.
    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.

Similarly to blackbox_exporter, snmp_exporter is meant to run on a few central machines and can be thought of like a "Prometheus proxy".

TLS and basic authentication

The SNMP Exporter supports TLS and basic authentication. This enables better control of the various HTTP endpoints.

To use TLS and/or basic authentication, you need to pass a configuration file using the --web.config.file parameter. The format of the file is described in the exporter-toolkit repository.

Note that the TLS and basic authentication settings affect all HTTP endpoints: /metrics for scraping, /snmp for scraping SNMP devices, and the web UI.

Generating configuration

Most use cases should be covered by our default configuration. If you need to generate your own configuration from MIBs, you can use the generator.

Use the generator if you need to customize which objects are walked or use non-public MIBs.

Large counter value handling

In order to provide accurate counters for large Counter64 values, the exporter will automatically wrap the value every 2^53 to avoid 64-bit float rounding. Prometheus handles this gracefully for you and you will not notice any negative effects.

If you need to disable this feature for non-Prometheus systems, use the command line flag --no-snmp.wrap-large-counters.

Once you have it running

It can be opaque to get started with all this, but in our own experience, snmp_exporter is honestly the best way to interact with SNMP. To make it easier for others, please consider contributing back your configurations to us. snmp.yml config should be accompanied by generator config. For your dashboard, alerts, and recording rules, please consider contributing them to https://github.com/prometheus/snmp_exporter/tree/main/snmp-mixin