Add DD-WRT installation rule with JFFS setup and configuration

Co-authored-by: tuanductran <69758022+tuanductran@users.noreply.github.com>

Author: Copilot

skills/nextdns-cli/SKILL.md

@@ -20,6 +20,7 @@ metadata:
 | [advanced-features](rules/advanced-features.md) | conditional forwarder, MAC address, subnet | Advanced routing and filtering |
 | [monitoring](rules/monitoring.md) | log, cache-stats, discovered clients | Monitor and debug DNS queries |
 | [platform-specific](rules/platform-specific.md) | router, OpenWrt, pfSense, Synology | Platform-specific configurations |
+| [ddwrt-installation](rules/ddwrt-installation.md) | DD-WRT, JFFS, NTP, router, time sync, DNSMasq | DD-WRT router installation and setup |
 | [troubleshooting](rules/troubleshooting.md) | diagnostic, connection test, DNS leak | Troubleshoot DNS issues |
 
 ## Efficiency Rules

skills/nextdns-cli/rules/ddwrt-installation.md

@@ -0,0 +1,114 @@
+---
+title: DD-WRT Installation
+impact: HIGH
+impactDescription: Without proper JFFS setup and installation procedures, NextDNS CLI will fail to persist on DD-WRT routers, causing DNS configuration loss after reboots and potential certificate errors due to time sync issues.
+type: capability
+tags: DD-WRT, JFFS, router, NTP, time sync, DNSMasq, SSH, router installation
+---
+
+# DD-WRT Installation
+
+**Impact: HIGH** - Essential setup for NextDNS CLI on DD-WRT routers with persistent configuration
+
+NextDNS CLI has no native GUI support on DD-WRT and must be installed on JFFS storage to ensure persistence across reboots. Proper setup requires enabling JFFS, configuring time synchronization, and protecting custom DNS settings.
+
+## Pre-requisites
+
+- NextDNS CLI has no native GUI support on DD-WRT
+- Must be installed on JFFS (JFFS2 filesystem) for persistence
+- Requires SSH access to the router
+- Router must have sufficient JFFS storage space
+
+## JFFS Enablement
+
+JFFS must be enabled and properly wiped before installing NextDNS CLI:
+
+1. Navigate to **Administration** > **Management** in the DD-WRT web GUI
+2. Locate the **JFFS2 Support** section
+3. Enable the following options:
+    - **Enable JFFS2**: Set to **Enable**
+    - **Clean JFFS2**: Set to **Enable** (only for initial setup or when wiping data)
+4. Click **Apply Settings**
+5. Wait for the router to process the changes
+6. After the flash storage is wiped, disable **Clean JFFS2** and click **Apply Settings** again
+7. Reboot the router to ensure JFFS is mounted properly
+
+**Important**: The "Clean JFFS2" option should only be enabled once during initial setup. Leaving it enabled will erase JFFS contents on every reboot.
+
+## Installation and Upgrade
+
+Connect to your DD-WRT router via SSH and run the universal installer:
+
+```bash
+sh -c "$(curl -sL https://nextdns.io/install)"
+```
+
+The installer will:
+- Detect DD-WRT as the platform
+- Install NextDNS CLI to `/jffs/nextdns/`
+- Configure the service to start automatically
+- Set up integration with DNSMasq
+
+### Upgrading
+
+To upgrade an existing NextDNS CLI installation, re-run the same installer command:
+
+```bash
+sh -c "$(curl -sL https://nextdns.io/install)"
+```
+
+The installer automatically detects existing installations and performs an upgrade.
+
+## Time Sync Workaround
+
+DD-WRT may experience x509 certificate errors during boot due to incorrect system time. To prevent this, configure an NTP forwarder:
+
+```bash
+/jffs/nextdns/nextdns config set forwarder 2.pool.ntp.org
+```
+
+This ensures that NTP queries for `2.pool.ntp.org` are forwarded to your upstream DNS, preventing certificate validation failures during the boot sequence when the system clock hasn't synchronized yet.
+
+## DNSMasq Persistence
+
+NextDNS CLI modifies the default DNSMasq configuration. To protect custom DNSMasq settings and ensure they persist across NextDNS updates:
+
+1. Create a persistent DNSMasq configuration file:
+
+    ```bash
+    mkdir -p /jffs/etc
+    touch /jffs/etc/dnsmasq.conf
+    ```
+
+2. Add your custom DNSMasq settings to `/jffs/etc/dnsmasq.conf`:
+
+    ```conf
+    # Example custom settings
+    dhcp-option=option:router,192.168.1.1
+    dhcp-option=option:dns-server,127.0.0.1
+    ```
+
+3. This file will be preserved when NextDNS CLI updates or modifies the main DNSMasq configuration
+
+**Why this matters**: NextDNS CLI edits the default DNSMasq configuration during installation and updates. Using a separate persistent file ensures your custom settings are not overwritten.
+
+## Troubleshooting
+
+If you encounter issues during installation, run the installer in debug mode to get detailed diagnostic output:
+
+```bash
+DEBUG=1 sh -c "$(curl -sL https://nextdns.io/install)"
+```
+
+Common issues and solutions:
+
+- **JFFS not mounted**: Verify JFFS is enabled in Administration > Management and reboot the router
+- **Installation fails**: Ensure you have sufficient JFFS storage space using `df -h /jffs`
+- **Certificate errors**: Apply the NTP forwarder workaround described above
+- **DNSMasq conflicts**: Check `/tmp/dnsmasq.conf` for conflicts with existing rules
+
+## Reference
+
+- [NextDNS CLI GitHub](https://github.com/nextdns/nextdns)
+- [NextDNS CLI Wiki](https://github.com/nextdns/nextdns/wiki)
+- [DD-WRT Documentation](https://wiki.dd-wrt.com/)