Purpose

The Python script in this repository will read all static DHCP mappings of an Ubiquiti EdgeRouter X and store them in a dnsmasq compatible hosts file.

This means you can add new DHCP static mappings to the EdgeRouter X, run this script to update the hosts file and therefor the DNS server / records. Of course you can also schedule this script by cron, so you no longer have run anything manually. Just add a new static mapping on the EdgeRouter X and the DNS will automatically be updated within a minute.

If configured properly, you can now add static DHCP mappings and your DNS service will resolv them properly.

Installation

Copy the script

Make sure you've a copy of the update script script and placed it on the filesystem of the EdgeRouter X.
We recommend you copy the script manually to /config/scripts/update-static-hosts.py or run:

sudo curl -o /config/scripts/update-static-hosts.py https://raw.githubusercontent.com/confirm/edgerouter-dnsmasq-updater/master/update-static-hosts.py

IMPORTANT: If you install the script in this path, the script will be left untouched by upgrades etc.

Running the script

To create or update the hosts file, you can simply run the following command:

sudo /config/scripts/update-static-hosts.py /config/user-data/hosts.static-mappings

In case the static mappings changed, the script will update the defined hosts file (i.e. /config/user-data/hosts.static-mappings ) and reload dnsmasq via SIGHUP.

IMPORTANT: The script will REPLACE the defined file, so you shouldn't define /etc/hosts as your static hosts file.

Configuration

Persistence

Please note, everything you touch on the filesystem directly, will be lost after an OS update or a config restore.
To make things persistent, you've to update the EdgeRouter X config by following these steps:

SSH into the EdgeRouter X
Enter the config mode by executing configure
Add the commands described below
Commit and save them by executing commit, followed by save

This ensures that your dnsmasq & cron config stays in place, even after an OS update or config restore.

HINT: You can also update this configuration in the EdgeRouter X WebUI under the Config Tree tab.

Task scheduler configuration

To keep the hosts file up-to-date, you want to add a cronjob which runs the script every minute:

set system task-scheduler task update-static-hosts crontab-spec "* * * * *"
set system task-scheduler task update-static-hosts executable path /config/scripts/update-static-hosts.py
set system task-scheduler task update-static-hosts executable arguments /config/user-data/hosts.static-mappings

DNS configuration

Before the EdgeRouter X resolves your new mapped hosts, you need to configure dnsmasq to use your newly created file.
We recommend the following configuration:

# Don't use the default /etc/hosts file.
set service dns forwarding options no-hosts

# Use /config/user-data/hosts.static-mappings for lookups.
set service dns forwarding options addn-hosts=/config/user-data/hosts.static-mappings 

# Never forward plain names (without a dot or domain part).
set service dns forwarding options domain-needed

# Never forward addresses in the non-routed address spaces.
set service dns forwarding options bogus-priv

# Add the domain to hostname lookups without a domain.
set service dns forwarding options expand-hosts
set service dns forwarding options domain=<your domain>

# Don't forward the local domain.
set service dns forwarding options local=/<your domain>/

If you want an additional file for host lookups (e.g. aliases), simply add a new hosts file with an additional addn-hosts option.