oott/README.md

OOTT

Easy to setup and use network device discovery and alert system

Licensed under AGPL v3. See LICENSE.

• What is OOTT?
• Getting started
  • Simple installation with Docker
  • Using the mobile apps
• Deeper dive
  • Installing OOTT as a Nix flake
  • Full list of configuration options
  • Using HTTPS and domain names with the mobile apps
• Things to keep in mind
  • Storage considerations
  • Privileges and network ports

What is OOTT?

OOTT runs behind the scenes and monitors your local network, notifying you when something changes. Its most relevant features are:

• Scans the network regularly using ARP probes, with additional mDNS, SSDP, DHCP and (optionally) SNMP discovery
• Notifies you when a new device is found
• Notifies you when a device changes its IP address or network interface vendor (based on its MAC address)
• Notifies you when a device comes back online after a configurable period of being offline

You configure and browse the data it collects through a companion app available on the web, desktop, iOS and Android.

Getting started

Simple installation with Docker

This is the quickest way to get OOTT running. OOTT is published on Docker Hub as a pre-built image, rzuasti/oott, and the steps below get you to a running service with the smallest possible configuration.

You need somewhere on the host to store the configuration file and the database (OOTT uses SQLite, so the database folder should be on local — not remote — storage):

mkdir -p /docker/oott/config
mkdir -p /docker/oott/db

The user that runs Docker needs read access to the config folder and read/write access to the db folder. You can use any paths you like as long as you keep the volume mappings below in sync.

Create a minimal oott.toml at /docker/oott/config/oott.toml:

[database]
path = "/db/oott.db" # Must be "/db/oott.db" for the Docker image (the mounted volume)

[web_server]
api_key = "CHANGE_ME" # API key the app uses to talk to the backend — change this!

[notifications]
method = "pushover" # Use "none" to only log notifications instead of sending them

[notifications.pushover]
token = ""    # Your Pushover application token
user_key = "" # Your Pushover user key

This is enough to start the service; every other option falls back to a sensible default. See Full list of configuration options for everything you can tune, and the full sample config for a commented, all-options file.

Create a docker-compose.yml at /docker/oott/docker-compose.yml:

name: oott

services:
  oott:
    image: rzuasti/oott:latest
    volumes:
      - /docker/oott/config:/config
      - /docker/oott/db:/db
    network_mode: host

Host networking is required so OOTT can see the multicast and broadcast traffic its scanners rely on (see Privileges and network ports).

Start the service from where you placed the compose file:

docker compose up -d

That's it. Check that everything is running with docker ps, and follow the logs with docker logs CONTAINER_ID -f.

Using the mobile apps

The OOTT app (web, desktop, iOS and Android) talks to the backend exclusively over its REST API on port 3000. Open the app's settings and point it at your backend's address on the local network over HTTP, for example http://192.168.1.50:3000, using the API key you set in web_server.api_key.

This is the simplest setup and needs no extra infrastructure, but it only works while your phone is on the same local network as the backend.

Important

On iOS, the direct HTTP connection only works when you use the backend's private-range IP address (192.168.x.x, 10.x.x.x, 172.16–31.x.x) or a *.local (mDNS/Bonjour) name. A custom internal domain (e.g. oott.mylan.com) served over plain HTTP is blocked by iOS App Transport Security, even when it resolves to a private IP. Use the IP address directly, or set up HTTPS.

Note

The first time the iOS app reaches your backend on the local network, iOS shows a one-time "find devices on your local network" prompt. This is expected — tap Allow to continue.

To use a domain name, or to reach the backend from outside the local network, set up TLS as described in Using HTTPS and domain names with the mobile apps.

Deeper dive

Installing OOTT as a Nix flake

OOTT comes with a pre-built NixOS flake that you can integrate into your configuration. If you are not using flakes you can use the flake code as a baseline and write your own derivation.

To integrate the OOTT flake into your config you generally do three things: add OOTT to your inputs, add its module and overlay, then enable and configure the service.

1. Add OOTT to your inputs — in your flake.nix inputs section:

inputs = {
  ...
  oott = {
    url = "github:rzuasti/oott";
    inputs.nixpkgs.follows = "nixpkgs";
  };
  ...
};

2. Add the OOTT module and overlay — in your flake.nix modules section:

...
modules = [
  ...
  oott.nixosModules.oott
  ({pkgs, ...}: {
    nixpkgs.overlays = [
      oott.overlays.default
      ];
  })
  ...
];
...

3. Enable and configure OOTT — in your configuration.nix (or an imported file). Set all options through the service definition; the keys mirror the config file options listed below:

{
  pkgs,
  ...
}
: {
  environment.systemPackages = with pkgs; [
    oott
  ];

  services.oott = {
    enable = true;
    database.path = "/var/lib/oott.db";
    # networking.interface = "eth0"; # Optional: auto-detected if not set
    log.level = "warn";
    arp_scanner.wait_between_scans = "30m";
    arp_scanner.sender_timeout = "1m";
    arp_scanner.scan_duration = "10m";
    notifications.method = "pushover";
    notifications.notify_when_not_seen_for = "1w";
    notifications.pushover.token = "YOUR API TOKEN GOES HERE";
    notifications.pushover.user_key = "YOUR USER TOKEN GOES HERE";
    retention.window = "365d";
    device_events.deduplication_window = "1m";
  };
}

Full list of configuration options

The system configuration lives in a single config file, which you can write in TOML, JSON or YAML. With Docker, TOML is recommended — the full sample config lists every supported option with comments. With the Nix flake, set the same options through the service definition (see above).

Options marked Required have no built-in default and must be set in your config file. Everything else falls back to the default shown if you omit it.

Option	Default value	Description
database.path	Required	Location of the system database. Must be /db/oott.db when using the Docker image.
networking.interface	auto-detected	Network interface to use for scans. Optional — if not set, the first non-loopback connected interface is used automatically.
log.level	warn	Log level to use (off, error, warn, info, debug, trace)
web_server.ip_address	Required	Address the API and web UI bind to. Use 0.0.0.0 to bind all interfaces.
web_server.port	Required	Port the API and web UI listen on.
web_server.api_key	Required	API key the app must present to use the backend.
arp_scanner.enabled	true	Whether to run the ARP scanner. The whole [arp_scanner] section is optional; omit it to use the defaults below. Set to false to turn it off.
arp_scanner.wait_between_scans	30m	Time to wait between each network scan (you can express it in seconds, minutes, hours, etc. as a suffix - for example: 30s, 10m, 1h)
arp_scanner.sender_timeout	1m	If the ARP sender process takes longer than this it will be stopped (for a class C network - 254 IPs - it should take less than a minute)
arp_scanner.scan_duration	10m	How long to wait for response packets on each scan (5m to 10m is a good timeframe for a class B or C network)
mdns_scanner.enabled	true	Whether to run the mDNS/Bonjour scanner. Set to false to turn it off.
mdns_scanner.probe_timeout	2s	When an mDNS-discovered IP is not in the OS ARP cache, how long to wait for a targeted ARP probe reply to resolve its MAC address
ssdp_scanner.enabled	true	Whether to run the SSDP/UPnP scanner. Set to false to turn it off.
ssdp_scanner.probe_timeout	2s	When an SSDP/UPnP-discovered IP is not in the OS ARP cache, how long to wait for a targeted ARP probe reply to resolve its MAC address
dhcp_scanner.enabled	true	Whether to run the DHCP scanner. Set to false to turn it off.
snmp_scanner.enabled	false	Whether to run the SNMP scanner. The whole [snmp_scanner] section is optional and the scanner stays off unless you add it; once the section is present it defaults to true.
snmp_scanner.target	Required	SNMP agent to poll, as host:port (e.g. your gateway: 192.168.1.1:161). The scanner reads the agent's ARP table over SNMPv2c — no local probing. Required when the [snmp_scanner] section is present.
snmp_scanner.community	Required	SNMPv2c read-only community string. Use a read-only community and never commit a real secret. Required when the [snmp_scanner] section is present.
snmp_scanner.wait_between_scans	10m	Time to wait between polls. Keep it well under the agent's ARP cache timeout so active devices aren't missed.
snmp_scanner.timeout	5s	Per-poll SNMP request timeout.
notifications.method	Required	For now just pushover, you can set this to "none" to avoid sending notifications (it will just log)
notifications.notify_when_not_seen_for	Required	Send a notification if a device comes back online after not being seen for this timeframe (you can use hours, weeks, etc.)
notifications.pushover.token	Required	Your pushover token goes here, just copy&paste from their website after creating the app (may be left empty when method is none)
notifications.pushover.user_key	Required	User key goes here, this is the account wide code for pushover (may be left empty when method is none)
retention.window	365d	How long to retain device events and notifications. Records older than this are purged daily. Accepts duration strings (e.g. 90d, 1y, 6m).
device_events.deduplication_window	1m	Suppress duplicate device events: if the same scanner sees the same device (same MAC and IPv4) again within this window, only one event is recorded. Accepts duration strings (e.g. 30s, 1m, 5m).

Using HTTPS and domain names with the mobile apps

To reach the backend through a domain name, or from outside the local network, put it behind a reverse proxy (nginx, Caddy, Traefik, …) that terminates TLS with a valid certificate from a trusted CA (for example Let's Encrypt), then point the app at the HTTPS URL (e.g. https://oott.example.com). This works on every platform — including iOS — with no further configuration.

Connect using the domain name the certificate is issued for, not an IP address. Self-signed certificates are not supported unless they are manually trusted on the device.

Things to keep in mind

Storage considerations

OOTT stores a timestamped event in the database for every device detected on every scan. Storage therefore scales with three factors: number of active devices, scan frequency, and the retention window.

Estimates by network size

The figures below assume a 1-minute scan duration (arp_scanner.scan_duration = 1m) with a 1-minute wait between scans (arp_scanner.wait_between_scans = 1m), giving 720 scans per day, and a 365-day retention window. Assume all devices are continuously online (worst case).

Network size	Active devices	Storage / year
Home network	20–50	~1–2 GB
Homelab	50–100	~2–4 GB
Small office	100–200	~4–7 GB
Medium office	200–500	~7–18 GB

The rough formula behind these numbers is:

storage ≈ devices × scans_per_day × 145 bytes × retention_days

where 145 bytes covers the database row and its index entry, and scans_per_day = 86400 / (scan_duration_seconds + wait_between_scans_seconds).

Tuning scan timings and retention to control storage

Storage is directly proportional to scan frequency and retention window. The two main levers are:

Scan interval — arp_scanner.wait_between_scans is the most effective knob. Increasing it reduces scans per day linearly:

wait_between_scans	Scans/day (with 1m scan)	Storage vs. 1m+1m
1m	720	1× (baseline)
4m	288	0.4×
15m	90	0.12×
30m	48	0.07×

A 15-minute wait (the default) cuts storage to about one eighth of the worst-case figures above — the medium office drops from up to 18 GB to roughly 2 GB per year.

Event deduplication — device_events.deduplication_window caps how often the same scanner can record an event for the same device. With several scanners (ARP, mDNS, SSDP, DHCP) reporting overlapping sightings, this collapses near-identical rows into one per scanner per device per window, trimming storage without changing scan timings. Widen it to keep fewer events; narrow it (or set it very small) to keep a finer-grained history.

Retention window — retention.window sets how far back history is kept. Halving the window halves the storage. Useful reference points:

retention.window	Use case
30d	Minimal footprint, recent activity only
90d	A quarter's worth of history
180d	Six months — good middle ground
365d	One year (default)

Recommended starting points by network type:

Network	wait_between_scans	retention.window	Approx. storage
Home	15m	365d	~100–250 MB
Homelab	5m	180d	~350–700 MB
Small office	5m	90d	~175–350 MB
Medium office	15m	90d	~175–450 MB

Privileges and network ports

OOTT binds to the following ports on the host where it runs:

Port	Protocol	Configurable	Used by
3000	TCP	Yes (web_server.port)	REST API and web UI
5353	UDP (multicast)	No — fixed	mDNS/Bonjour scanner
1900	UDP (multicast)	No — fixed	SSDP/UPnP scanner
67	UDP (broadcast)	No — fixed	DHCP scanner

The mDNS (UDP 5353), SSDP (UDP 1900) and DHCP (UDP 67) ports are fixed by their respective protocols and cannot be changed. They must be available on the server where OOTT runs.

OOTT binds these sockets with address/port reuse, so it can run alongside other responders already listening on them (for example avahi on 5353, minidlna on 1900, or a DHCP server/relay on 67). However, the ports must not be blocked by a host firewall, and the corresponding multicast/broadcast traffic must be allowed to reach the host — otherwise the scanners will not discover any devices.

Important

OOTT needs elevated privileges: the ARP scanner requires raw-socket access, and port 67 is a privileged port. The pre-built Docker image and NixOS module already run with what they need.

Under Docker, the scanners require host networking (or an equivalent setup that exposes the host's multicast and broadcast traffic to the container), as shown in the Docker installation above.