SUB-ALIGATOR

A simple internal web application for tracking and automatically allocating IPv4 subnets.

Purpose

This application is intended solely for internal tracking and automatic allocation of IPv4 subnets. It is not a general IPAM, monitoring tool, device inventory, VLAN manager, or network topology viewer.

It is designed to run only inside a LAN/VPN. The application does not include authentication and must be placed behind a firewall/reverse proxy in a trusted network.

Features

• Manage one or more IP pools manually through the web UI.
• First-run setup wizard: create the first pool before allocating subnets.
• Automatic subnet allocation using a first-fit algorithm for prefixes /20 through /30.
• Atomic allocation writes using SQLite BEGIN IMMEDIATE transactions.
• Retro TUI/terminal-style web UI, server-side rendered with Askama.
• Dynamic preview of the next free subnet via HTMX.
• Allocation history with filtering, search, and pagination.
• Release subnets (status released) with a mandatory note, directly from the history table or detail page.
• Released subnets free up address space and can be reused by the first-fit algorithm.
• Delete pools without losing their allocations: the subnets stay in history and keep blocking the address range if the same or an overlapping pool is added again.
• Light and dark (amber terminal) theme, switchable in the page header and remembered per browser.
• Audit log of all operations.
• Markdown, CSV, and JSON exports.
• SQLite migrations run automatically on startup.
• Backup and restore scripts.

Architecture

• Rust edition 2024
• Axum + Tokio
• SQLx with SQLite
• Askama for HTML templates
• HTMX from a local static file
• Custom CSS without external frameworks
• CIDR/IP calculations using ipnet

Quick start

cd sub-aligator
cp .env.example .env
docker compose up -d --build

Open a browser at:

http://SERVER_IP:8080

On first launch you will be asked to create the first pool. The default port can be changed in .env via the APP_PORT variable.

Persistent data

Docker Compose creates local directories:

• ./data – SQLite database
• ./exports – generated exports (Markdown, CSV, JSON)
• ./backups – database backups

These directories are bind-mounted into the container, so data persists even if the container is removed.

Backup and restore

Backup

./scripts/backup.sh

The script creates a consistent database backup using sqlite3 .backup with a UTC timestamp in the filename. Backups are stored in ./backups.

Restore

./scripts/restore.sh ./backups/subnet-allocator.db.20240930T120000Z.backup

Warning: restore overwrites the current database. Stop the container and back up the current state before restoring.

Automating backups

On the host you can use a systemd timer or cron. Example cron entry:

0 2 * * * /path/to/sub-aligator/scripts/backup.sh >> /var/log/subnet-allocator-backup.log 2>&1

Exports

After every successful allocation or release, read-only exports are regenerated:

• /app/exports/allocations.md
• /app/exports/allocations.csv
• /app/exports/allocations.json

They are also available for download via endpoints:

• GET /exports/allocations.md
• GET /exports/allocations.csv
• GET /exports/allocations.json

The Markdown export contains a separate section for each pool with a table of active and reserved allocations. CSV and JSON include all allocations, including released ones.

Security notes

• The application has no authentication. Use it only behind a VPN/LAN/firewall.
• CSRF tokens are required for POST forms.
• Security headers are set: X-Content-Type-Options, X-Frame-Options, Referrer-Policy, Content-Security-Policy.
• The application has no default Internet exposure; port binding is handled by Docker Compose.
• /healthz returns only {"status":"ok"}.

Adding authentication later via Caddy + Authentik

The application is prepared for authentication through a trusted reverse proxy. The function get_actor_from_request() in src/audit.rs currently returns local, but can be updated to read a header such as X-Authentik-Username.

Example Caddy configuration with Authentik:

subnet.example.com {
    reverse_proxy /outpost.goauthentik.io/* http://authentik:9000
    forward_auth http://authentik:9000 {
        uri /outpost.goauthentik.io/auth/caddy
        copy_headers X-Authentik-Username X-Authentik-Groups X-Authentik-Email
    }
    reverse_proxy subnet-allocator:8080
}

After updating get_actor_from_request(), the audit log will record the real user.

First-fit allocation example

1. First request /30 receives 10.91.0.0/30.
2. Next request /24 receives 10.91.1.0/24 (avoids the occupied /30).
3. Another request /30 fills the gap and receives 10.91.0.4/30.

The algorithm always respects CIDR alignment and finds the first free space large enough.

Endpoints

• GET / – main page
• GET /healthz – healthcheck
• GET /setup – first-run pool setup
• GET /pools – pool management
• POST /pools/new – create a new pool
• GET /partials/pools/{slug}/preview?prefix_length=24 – HTMX preview
• POST /allocations – create an allocation
• GET /allocations/{id} – allocation detail
• POST /allocations/{id}/release – release an allocation
• GET /exports/allocations.{md,csv,json} – exports

Troubleshooting

Container does not start

docker compose logs -f subnet-allocator

Database is locked

If the process terminates unexpectedly, a -wal or -shm file may remain. Stop the container and check ./data.

Exports are not generated

Check the permissions of the ./exports directory and the APP_EXPORTS_DIR variable.

Licence

MIT. See the LICENSE file.