ASUS Router Operations

Facts verified as of 2026-07.

Authoritative guidance for configuring and hardening ASUS routers — stock Asuswrt and Asuswrt-Merlin firmware — via the web UI and SSH/nvram. Covers security hardening, encrypted DNS, VPN, network segmentation, AiMesh, AiProtection, and JFFS scripting.

Safety first. Changes here can lock you out or drop the network. Test during low-usage windows, document the before value, and know how to undo. Cite official docs, not folklore.

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Stock Asuswrt vs Asuswrt-Merlin

	Stock Asuswrt	Asuswrt-Merlin
Base	ASUS official	Community fork of ASUS source (same core, more control)
Scripting	Limited	JFFS custom scripts, cron, services-start, firewall-start, nat-start
DNS control	Basic	DNS Director (per-client/global DNS redirection, DoT)
VPN	OpenVPN/WireGuard server+client	+ VPN Director (policy/split-tunnel routing)
Best for	Most users	Power users wanting scripts, fine-grained DNS/VPN routing

Never mix stock and Merlin nodes in the same AiMesh network. Keep the firmware family consistent across mesh nodes.

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Security hardening checklist

Do these on every new router, in order:

1. Change defaults immediately — both the admin/login password and the WiFi password.
2. Disable WPS — it's a brute-force surface.
3. Disable UPnP unless an app genuinely needs it (it creates unpredictable port forwards).
4. Use explicit port forwarding, never DMZ — DMZ exposes the entire device.
5. Disable remote WAN admin access — use a VPN to manage remotely instead.
6. Enable AiProtection (two-way IPS + malicious-site blocking) where available.
7. Set up a guest network with intranet access disabled (proper isolation).
8. Enable firewall logging for security monitoring; forward to syslog if you have a collector.
9. Apply ingress filtering (BCP38/84 anti-spoofing) where supported.
10. Keep firmware current — security fixes land in point releases.

See references/hardening-and-network.md for the full hardening rationale, VLAN/IoT segmentation, AiMesh backhaul tuning, QoS, and dual-WAN.

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DNS privacy stack

Layer	What	Notes
Transport	DoT (DNS over TLS) or DoH (DNS over HTTPS)	Stops plaintext port-53 hijacking. Merlin DNS Director can enforce DoT
Provider	Cloudflare (1.1.1.1), NextDNS, ControlD, AdGuard	Choose for filtering/analytics needs
Validation	DNSSEC	Validates record authenticity
Per-client policy	DNS Director (Merlin)	Different DNS per device/profile; split-horizon
Rebinding protection	On by default	Can break local services (Plex, smart home) — whitelist specific domains rather than disabling wholesale

Avoid plain DNS (port 53) — unencrypted and hijackable. Move to DoT/DoH.

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VPN decision table

Need	Use
Fast modern tunnel, low overhead	WireGuard server/client (preferred where supported)
Maximum compatibility / legacy clients	OpenVPN server/client
Route only some clients/traffic through VPN	VPN Director (Merlin) — policy-based split tunnel
Remote admin of the router	VPN in, then manage on LAN (never expose WAN admin)

Common clients: NordVPN, Surfshark, Mullvad via OpenVPN/WireGuard config import.

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Network segmentation

Goal	Approach
Visitor isolation	Guest network with "Access Intranet" off
IoT containment	Dedicated guest/VLAN SSID; block lateral movement to main LAN
Consistent guest across mesh	Enable guest on AiMesh deliberately; mind "Access Intranet" per node
Smart-home discovery	mDNS/Bonjour may need controlled cross-VLAN allowances — scope narrowly
Segmented routing	VLAN segmentation + routing policies (capability varies by model)

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Patterns to avoid

Anti-pattern	Why	Instead
DMZ mode	Exposes the whole device to the internet	Explicit per-port forwarding
UPnP globally on	Unpredictable auto port forwards	Enable only when required, understand the risk
Plain DNS (port 53)	Plaintext, hijackable	DoT/DoH
Mixing stock + Merlin in AiMesh	Inconsistent behavior	Keep firmware family uniform
Disabling DNS rebind protection wholesale	Reopens rebinding attacks	Whitelist the specific local domains that break
Wireless mesh backhaul on congested channels	Throughput collapse	Wired backhaul or dedicated DFS 5GHz channel
Default admin/WiFi credentials	Trivial compromise	Change both immediately
Remote WAN admin enabled	Major attack surface	Manage via VPN

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Operating principles

1. Reversibility — record the current value before changing; know the undo path.
2. Testability — change during low-usage windows; verify before walking away.
3. Trade-offs — note privacy-vs-functionality costs (rebind protection vs local services).
4. Verification — confirm via system log, client-side test (e.g. DNS leak test), or nvram get.
5. Cite official docs — avoid unverified tweaks.

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SSH / JFFS scripting (Merlin)

Merlin runs user scripts from JFFS at lifecycle points. Enable JFFS custom scripts and configs (Administration → System) first.

Script	Runs at	Use for
services-start	After services start	Start custom daemons
firewall-start	After firewall (re)builds	Add custom iptables rules (survives firewall restarts)
nat-start	After NAT rules load	Custom NAT/port rules
dnsmasq.postconf	Before dnsmasq starts	Inject dnsmasq config

Inspect/set persistent config with nvram get <key> / nvram set <key>=<val> + nvram commit (commit sparingly — it writes flash).

The assets/firewall-start.sh template shows the canonical safe shape for custom firewall rules. See references/hardening-and-network.md for placement and gotchas.

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Assets

File	Use
assets/firewall-start.sh	Annotated Merlin /jffs/scripts/firewall-start template — idempotent custom iptables rules with safe-by-default examples

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See also

• net-ops — general networking: subnets, DNS, TLS, firewalls, packet inspection

Key external resources

• Asuswrt-Merlin project · docs · wiki
• Merlin features (DNS Director, VPN Director)
• ASUS router security hardening FAQ
• ASUS firewall intro · Network Services Filter · IPv6 firewall
• AiProtection overview · setup
• Cloudflare DoH · ControlD ASUS setup
• SNBForums community