Configuring a Network Side Router (OpenWRT): A Comprehensive Guide

This article provides a detailed tutorial on setting up a side router (also known as a “bypass router”) using OpenWRT. It explores the advantages and disadvantages of this network configuration, offering a balanced perspective for professionals, developers, and tech enthusiasts. The guide covers configuration steps, troubleshooting tips, and a discussion of common controversies surrounding side routers.

Understanding the Side Router Concept

A side router is a separate router, often running a custom firmware like OpenWRT, that sits alongside the main router in a network. Instead of replacing the main router, the side router handles specific tasks, such as VPN connections, ad blocking, or customized routing rules. This setup allows for flexibility and experimentation without disrupting the core network functionality.

Setting Up OpenWRT as a Side Router: Step-by-Step

The following steps outline how to configure an OpenWRT device as a side router:

Initial Setup: Flash OpenWRT onto a compatible router following standard OpenWRT installation procedures.
Connect to the Main Router: Connect the OpenWRT router to the main router via LAN ports on both devices.
Configure the OpenWRT LAN Interface:
- Assign a static IP address to the OpenWRT LAN interface within the same subnet as the main router (e.g., if the main router is 192.168.1.1, set the OpenWRT router to 192.168.1.2).
- Set the gateway to the main router’s IP address (e.g., 192.168.1.1).
- Set the DNS server to the main router’s IP address.
Disable DHCP on the Main Router: To avoid IP address conflicts, disable the DHCP server on the main router and enable it on the OpenWRT device.
Enable DHCP on OpenWRT: Configure the OpenWRT device to act as a DHCP server to assign IP addresses to devices on your network.

Ethernet cable plugged into the LAN port of a router

Configuring Custom Routing Rules

One of the primary benefits of a side router is the ability to create custom routing rules. This can be achieved through OpenWRT’s configuration files or web interface.

Access OpenWRT Interface: Access the OpenWRT web interface via its assigned IP address (e.g., 192.168.1.2).
Static IP Assignment: Assign static IP addresses to specific devices on your network, if required. This ensures these devices always receive the same IP address.
Policy Based Routing: Use the OpenWRT’s built-in firewall to selectively route traffic through the side router based on source IP address, destination IP address, or port.

Addressing Common Issues and Controversies

Side router setups can introduce complexities and potential issues. Here are some common concerns and solutions:

Asymmetrical Routing: Data packets may take different paths for outgoing and incoming traffic, leading to connection problems. Enabling “Masquerading” (NAT) on the OpenWRT router can often resolve this.
DNS Leaks: Ensure all devices are using the OpenWRT router for DNS resolution to prevent DNS leaks, especially when using VPNs.
IPv6 Configuration: Properly configure IPv6 or disable it if not needed, as incorrect IPv6 settings can bypass the side router.

Router interface showing firewall settings and NAT configuration

When is a Side Router the Right Choice?

A side router is a good option for users who want to:

Experiment with network configurations without impacting the primary network.
Implement custom routing rules for specific devices or applications.
Offload resource-intensive tasks from the main router.

However, a side router may not be suitable for:

Users who require a simple and straightforward network setup.
Complex network environments where troubleshooting can be challenging.

Alternatives to Side Routers

Consider these alternatives if a side router isn’t ideal:

Advanced Router Firmware: Some routers offer advanced firmware options that provide similar functionality to OpenWRT without requiring a separate device.
Virtualization: Running OpenWRT as a virtual machine on a server can provide similar benefits with more flexibility.

A network diagram illustrating a side router setup in a home network

Conclusion

Side routers offer a powerful way to customize and enhance network functionality. By understanding the configuration steps, potential issues, and alternatives, users can make an informed decision about whether a side router is the right solution for their needs. While it is not without its complexities and controversies, it remains a viable option for tech enthusiasts seeking greater control over their home or small business network.