# 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 using the `public_v2` auth module,
which should be a read-only access community on the target device.

Note, community strings in SNMP are not considered secrets, as they are sent
unencrypted in SNMP v1 and v2c. For secure access, SNMP v3 is required.

# 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](http://www.oidview.com/mibs/0/IF-MIB.html).

## 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](https://github.com/prometheus/snmp_exporter/releases) page and need no
special installation.

We also provide a sample [systemd unit file](examples/systemd/snmp_exporter.service).

## Running

Start `snmp_exporter` as a daemon or from CLI:

```sh
./snmp_exporter
```

Visit <http://localhost:9116/snmp?target=192.0.0.8> where `192.0.0.8` is the IP or
FQDN of the SNMP device to get metrics from. Note that this will use the default transport (`udp`),
default port (`161`), default auth (`public_v2`) and default module (`if_mib`). The auth and module
must be defined in the `snmp.yml` file.

For example, if you have an auth named `my_secure_v3` for walking `ddwrt`, the URL would look like
<http://localhost:9116/snmp?auth=my_secure_v3&module=ddwrt&target=192.0.0.8>.

To configure a different transport and/or port, use the syntax `[transport://]host[:port]`.

For example, to scrape a device using `tcp` on port `1161`, the URL would look like
<http://localhost:9116/snmp?auth=my_secure_v3&module=ddwrt&target=tcp%3A%2F%2F192.0.0.8%3A1161>.

Note that [URL encoding](https://en.wikipedia.org/wiki/URL_encoding) should be used for `target` due
to the `:` and `/` characters. Prometheus encodes query parameters automatically and manual encoding
is not necessary within the Prometheus configuration file.

## 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](#generating-configuration).

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

## Prometheus Configuration

The URL params `target`, `auth`, and `module` can be controlled through relabelling.

Example config:
```YAML
scrape_configs:
  - job_name: 'snmp'
    static_configs:
      - targets:
        - 192.168.1.2  # SNMP device.
        - switch.local # SNMP device.
        - tcp://192.168.1.3:1161  # SNMP device using TCP transport and custom port.
    metrics_path: /snmp
    params:
      auth: [public_v2]
      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](https://github.com/prometheus/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](https://github.com/prometheus/exporter-toolkit/blob/master/docs/web-configuration.md).

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](snmp.yml).
If you need to generate your own configuration from MIBs, you can use the
[generator](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>.
