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Reverse DNS

Setting up better name discovery with Reverse DNS

If you are running a DNS server, such as AdGuard, set up Private reverse DNS servers for a better name resolution on your network. Enabling this setting will enable NetAlertX to execute dig and nslookup commands to automatically resolve device names based on their IP addresses.

Tip

Before proceeding, ensure that name resolution plugins are enabled.
You can customize how names are cleaned using the NEWDEV_NAME_CLEANUP_REGEX setting.
To auto-update Fully Qualified Domain Names (FQDN), enable the REFRESH_FQDN setting.

Example 1: Reverse DNS disabled

jokob@Synology-NAS:/$ nslookup 192.168.1.58 ** server can't find 58.1.168.192.in-addr.arpa: NXDOMAIN

Example 2: Reverse DNS enabled

jokob@Synology-NAS:/$ nslookup 192.168.1.58 45.1.168.192.in-addr.arpa name = jokob-NUC.localdomain.

Enabling reverse DNS in AdGuard

  1. Navigate to Settings -> DNS Settings
  2. Locate Private reverse DNS servers
  3. Enter your router IP address, such as 192.168.1.1
  4. Make sure you have Use private reverse DNS resolvers ticked.
  5. Click Apply to save your settings.

Specifying the DNS in the container

You can specify the DNS server in the docker-compose to improve name resolution on your network. 

services:
  netalertx:
    container_name: netalertx
    image: "ghcr.io/jokob-sk/netalertx:latest"
    restart: unless-stopped
    volumes:
      -  /home/netalertx/config:/app/config
      -  /home/netalertx/db:/app/db
      -  /home/netalertx/log:/app/log
    environment:
      - TZ=Europe/Berlin
      - PORT=20211
    network_mode: host
    dns:           # specifying the DNS servers used for the container
      - 10.8.0.1
      - 10.8.0.17

Using a custom resolv.conf file

You can configure a custom /etc/resolv.conf file in docker-compose.yml and set the nameserver to your LAN DNS server (e.g.: Pi-Hole). See the relevant resolv.conf man entry for details.

docker-compose.yml:

version: "3"
services:
  netalertx:
    container_name: netalertx
    image: "ghcr.io/jokob-sk/netalertx:latest"
    restart: unless-stopped
    volumes:
      - ./config/app.conf:/app/config/app.conf
      - ./db:/app/db
      - ./log:/app/log
      - ./config/resolv.conf:/etc/resolv.conf                          # Mapping the /resolv.conf file for better name resolution
    environment:
      - TZ=Europe/Berlin
      - PORT=20211
    ports:
      - "20211:20211"
    network_mode: host

./config/resolv.conf:

The most important below is the nameserver entry (you can add multiple):

nameserver 192.168.178.11
options edns0 trust-ad
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