You cannot assign different firewall rules to WAN and LAN traffic on a single physical Ethernet port of a Teltonika router because the hardware lacks the isolation required for distinct network zones. A standard RJ45 interface acts as a simple Layer 2 bridge or switch port, meaning all ingress and egress traffic shares the same broadcast domain and security context. To achieve separate security policies, you must use two distinct physical ports or implement VLAN tagging on an upstream managed switch that separates the logical networks before they reach the router’s single interface.
The Hardware Limitation of Single-Port Segmentation
The core misunderstanding in this configuration request is assuming that software firewall rules can create physical network boundaries where none exist at the hardware level. When you plug a cable into the
ETH0 port (or any generic Ethernet port) on devices like the TRB140 or RUTX series, the router treats it as a unified interface. It does not inherently know which packets are "WAN" and which are "LAN" based solely on the physical connector. Instead, it relies on IP addressing schemes and routing tables to determine traffic direction.
If you connect both your ISP modem and your internal office switch to the same port via a passive splitter (which is physically impossible with standard copper wiring) or a hub, all devices will be on the same subnet. Firewalls operate on interfaces or subnets, not individual wires within a single interface. Therefore, applying a strict "deny all" rule to the WAN zone would inadvertently block your local LAN devices if they share the same physical entry point. This architectural constraint ensures that network segmentation requires either multiple physical ports or external logical separation through VLANs.
For users looking to optimize their overall network layout after realizing these limitations, understanding how to properly segment traffic across available ports is crucial. You might find our guide on
Reworking Home Network: Improving LAN/WAN Reach with Firewall, Router, and Server helpful for structuring your internal zones once you have established proper physical separation.
Why Physical Separation is Mandatory
In networking, the term "WAN" typically refers to the untrusted external network, while "LAN" refers to the trusted internal network. The firewall's primary job is to filter traffic between these trust levels. If both networks enter through the same hole in the wall, the router sees only one stream of data. Without VLAN tagging from an upstream device, there is no way for the Teltonika firmware to distinguish a packet coming from the ISP versus a packet coming from your desktop computer. They are indistinguishable at the MAC address layer until they are routed.
Attempting to force this behavior without proper infrastructure leads to security vulnerabilities. If you configure the same port for both roles using complex IP masquerading tricks, you risk exposing internal services to the public internet because the boundary between "inside" and "outside" becomes blurred. This is why Teltonika designs its routers with dedicated WAN and LAN ports on most models, or provides multiple Gigabit Ethernet ports that can be logically assigned to different zones.
Alternative Solution: Using Multiple Ports
The most reliable method to apply different firewall rules is to utilize the additional Ethernet ports available on your Teltonika model. Most industrial routers, such as the RUTX11 or FMB920, come with at least two or more Ethernet ports. You can assign one port exclusively to the WAN connection and another to the LAN uplink.
In the TronOS web interface, navigate to
Network > Interfaces. Here you will see a list of available interfaces. Create a new interface for your LAN by selecting an unused Ethernet port (e.g., ETH1). Assign it a static IP address within your private range, such as
192.168.10.1/24. Then, ensure your existing WAN interface (usually ETH0 or PPPoE) remains configured for the external connection. Once separated, you can go to
Firewall > Zones and define strict rules. For example, allow all outbound traffic from the LAN zone to the WAN zone, but restrict inbound traffic from WAN to LAN to specific forwarded ports only. This setup guarantees that even if the WAN side is compromised, the attacker cannot directly access the LAN subnet because the firewall explicitly blocks inter-zone communication unless permitted.
Advanced Alternative: VLAN Tagging with Managed Switches
If you are strictly limited to a single physical cable running from the wall to the router, you must introduce a managed switch between the wall outlet and the router. This approach requires support for IEEE 802.1Q VLANs on both the switch and the Teltonika router.
First, configure your managed switch to tag traffic from the ISP with VLAN ID 100 (WAN) and traffic from your local devices with VLAN ID 200 (LAN). Then, connect the switch to the Teltonika router via a trunk port. In the router’s
Network > Interfaces, you will need to create virtual interfaces for these VLANs. For instance, create an interface named
vlan100 on top of the physical ETH0 port, tagged with ID 100, and assign it the WAN PPPoE or DHCP settings. Similarly, create
vlan200 with ID 200 for your LAN DHCP server.
Once these virtual interfaces are created, the firewall treats them as distinct entities. You can now apply zone-based firewall rules exactly as you would with separate physical ports. However, note that not all Teltonika models support VLAN tagging on all firmware versions, and this setup adds significant complexity. For most home or small business users, adding a second cable or using a second router is far more stable than managing VLANs on industrial hardware. If you are dealing with multiple routers sharing a single WAN source, consider reading
Sharing One WAN Source with Two WiFi Routers: Different LANs, Different Passwords for a simpler architectural alternative.
Common Pitfalls in Configuration
When attempting to split traffic, many users mistakenly try to use MAC filtering or IP whitelisting on a single interface to simulate security zones. This is ineffective because MAC addresses can be spoofed, and IP ranges can overlap. True security comes from the firewall zone definition, which requires logical separation. Another common error is enabling NAT twice. If you have a VLAN setup, ensure that only the WAN-facing virtual interface performs NAT for the internal VLANs. Double NAT can cause connectivity issues and makes troubleshooting difficult. Always verify your routing table in
System > Diagnostics > Ping to ensure packets are flowing correctly between the virtual interfaces and the external gateway.
Frequently Asked Questions
Can I use a USB-to-Ethernet adapter to create a second WAN port?
Yes, most Teltonika routers running TronOS support USB Ethernet adapters, allowing you to add an extra physical interface. You can then assign this new interface to the WAN zone in the firewall settings, providing true physical separation from your existing LAN port.
What happens if I connect my PC and Modem to the same port via a cheap hub?
Both devices will end up in the same broadcast domain and subnet. The firewall cannot distinguish between them, so any rule applied to the interface affects both equally. This creates a severe security risk where internal devices are exposed to the same threats as the external network.
Does the RUTX50 support dual WAN on a single port?
No, the RUTX50 has only one Ethernet port. It supports dual WAN functionality only if you use a secondary connection type, such as cellular (4G/LTE) alongside the Ethernet WAN. You cannot split the single Ethernet port into two independent network segments without external VLAN equipment.
Is it possible to isolate guests on the same Wi-Fi SSID as the main LAN?
Yes, but this is done via Client Isolation features, not by changing the WAN/LAN port configuration. In the Wireless settings, you can enable "Client Isolation" or create a separate Guest SSID that routes to a different VLAN or firewall zone, keeping guests off the main LAN while using the same physical radio.
Why did my internet stop working after creating a VLAN interface?
This usually occurs because the VLAN tag was not stripped before reaching the ISP modem, or the modem expects untagged traffic. Ensure that the VLAN interface on the router is configured correctly, and check if your ISP requires specific tagging (like VLAN 10 for fiber providers) which should be applied to the WAN virtual interface, not the LAN one.