What is a Soft Router?

A soft router, also known as a software router or virtual router, is a computer program that performs the functions of a traditional hardware router. Unlike physical routers which have dedicated hardware and firmware, a soft router runs as a software application on a general-purpose computer or server.

The main purpose of a soft router is to route and forward data packets between different networks, just like a hardware router does. It examines incoming packets, determines the best path for each packet based on its destination IP address, and forwards the packets to the appropriate outgoing interface.

Advantages of Soft Routers

Soft routers offer several advantages over traditional hardware routers:

1. Cost-effective: Soft routers can be run on commodity hardware, making them much more affordable than dedicated hardware routers. There’s no need to purchase expensive, proprietary hardware.

2. Flexible: Software can be easily modified and updated, allowing for greater flexibility and customization. New features and protocols can be added through software updates.

3. Scalable: Soft routers can scale up by adding more computing resources (CPU, memory, storage) to the host system. This is often easier and cheaper than upgrading to a higher-end hardware router.

4. Multi-purpose: The host computer can run other network services and applications alongside the soft router, making efficient use of hardware resources.

5. Remote management: Soft routers can be easily managed remotely via SSH, web interfaces, or APIs, without requiring physical access to the device.

How Does a Soft Router Work?

A soft router performs the same basic functions as a hardware router, but does so entirely in software running on a general-purpose operating system like Linux.

Key Components

1. Network Interfaces: A soft router needs at least two network interfaces to connect different networks. These can be physical interfaces (Ethernet, Wi-Fi) or virtual interfaces (VLAN, tunnel).

2. Routing Table: The routing table is a database that contains information about network destinations and the best paths to reach them. The soft router uses this to make forwarding decisions.

3. Forwarding Engine: This is the part of the soft router that actually moves packets from incoming to outgoing interfaces based on the routing table. It’s implemented entirely in software.

4. Routing Protocols: Soft routers can run routing protocols like OSPF, BGP, RIP to exchange routing information with other routers and build the routing table dynamically.

Packet Flow

Here’s a simplified view of how a packet flows through a soft router:

1. A packet arrives on one of the soft router’s network interfaces.
2. The forwarding engine examines the packet’s destination IP address.
3. The forwarding engine consults the routing table to find the best path (outgoing interface and next hop) for that destination.
4. The forwarding engine forwards the packet out the appropriate outgoing interface.
5. If no matching route is found, the packet is dropped.

This process is repeated for every incoming packet, allowing the soft router to efficiently move traffic between networks.

Setting Up a Soft Router

Setting up a basic soft router is relatively straightforward. You’ll need a computer with at least two network interfaces (Ethernet NICs are most common) and a Unix-like operating system (Linux is the most popular choice).

Hardware Requirements

• A computer with a multi-core 64-bit CPU (x86-64)
• At least 4GB of RAM (more for higher throughput)
• Two or more Gigabit Ethernet interfaces
• Sufficient storage for the OS and software (SSD recommended)

Software Requirements

• A Linux distribution (Debian, Ubuntu, CentOS, etc.)
• Linux kernel 4.x or later with forwarding enabled
• IP routing utilities (iproute2)
• Routing software (Bird, FRR, Quagga)

Basic Configuration Steps

1. Install your chosen Linux distribution on the hardware.
2. Configure the network interfaces with appropriate IP addresses and bring them up.
3. Enable IP forwarding in the kernel:
   echo "net.ipv4.ip_forward=1" >> /etc/sysctl.conf
sysctl -p
4. Configure static routes or install and configure routing protocol software.
5. Configure the firewall to allow forwarding between the interfaces.
6. Test connectivity and routing between the connected networks.

There are also pre-built soft router distributions like VyOS and OpenWRT that bundle all necessary components into a ready-to-use system, which can simplify setup for common use cases.

Use Cases for Soft Routers

Small Office/Home Office (SOHO) Routing

Soft routers are a cost-effective solution for routing in small office and home networks. A spare PC or even a Raspberry Pi can be used to route between the local network and the internet, while also running services like DHCP and DNS.

Virtual Private Networks (VPNs)

Soft routers are often used to terminate VPNs and route traffic between the VPN and local networks. Popular VPN protocols like OpenVPN, WireGuard, and IPsec are well supported on Linux-based soft routers.

Lab and Education

Soft routers are ideal for learning and experimenting with routing and networking concepts. Students and researchers can easily set up complex network topologies using virtual machines and soft routers, without needing expensive hardware.

Cloud Networking

In cloud environments, soft routers are used extensively for connecting virtual networks, VPNs, and hybrid cloud setups. Cloud platforms often provide managed soft router instances, but users can also deploy their own on virtual machines.

Software-Defined Wide Area Networking (SD-WAN)

SD-WAN solutions often use soft routers at branch sites to connect to the WAN and enforce policies. The centralized SD-WAN controller communicates with the soft routers to push configurations and monitor performance.

Limitations of Soft Routers

Performance

Soft routers are limited by the performance of their host hardware. A busy soft router may struggle to keep up with line rate on multiple gigabit interfaces, especially if it’s also running other services. Dedicated hardware routers have specialized ASICs and FPGAs that can process packets much faster.

Reliability

Soft routers are as reliable as the hardware they run on. A hardware failure or OS crash will take down the router. In contrast, hardware routers are purpose-built for reliability with features like redundant power supplies and hot-swappable components.

Scalability

While soft routers can scale by adding more hardware resources, there are practical limits. Very high bandwidth (10+ Gbps) and high packet rates (millions of pps) are still the domain of hardware routers. Soft routers are better suited for small to mid-scale deployments.

Feature Support

While soft routers are very flexible, they may not support all the advanced features found in high-end hardware routers, such as hardware-accelerated encryption, deep packet inspection, or complex QoS hierarchies. The feature set depends on the software used and the underlying OS and hardware capabilities.

FAQ

1. Can a soft router replace a hardware router completely?

In many cases, yes. Soft routers are a viable alternative to hardware routers in small to medium scale deployments where their performance and reliability limitations are acceptable. However, hardware routers are still the best choice for very high bandwidth, high availability, and advanced feature requirements.

2. What hardware should I use for a soft router?

The hardware requirements depend on your performance needs. A simple soft router for a home network can run on a Raspberry Pi or an old PC. For higher throughput, a multi-core server with good NICs and plenty of RAM is recommended. Always overprovision hardware to leave headroom for spikes.

3. What software should I use for a soft router?

There are many options, depending on your needs and expertise:
– Linux with IP routing utilities: The most basic and flexible setup. Requires manual configuration.
– Specialized soft router distros: Vyos, OpenWRT, pfSense, etc. Easier to set up and manage.
– Containerized routing software: Run FRR, Bird, Quagga in Docker containers for easy deployment.
– Cloud-native solutions: Use cloud instances with routing software for cloud networking.

The best choice depends on your specific requirements and environment.

4. How do I ensure high availability with soft routers?

High availability requires redundancy at the hardware, software, and network levels. Some strategies:
– Use redundant hardware and power supplies.
– Set up multiple soft routers in a failover or load-sharing configuration (e.g., using VRRP).
– Use monitoring and failover scripts to detect and recover from failures.
– Regularly back up configurations and use version control.

However, for mission-critical applications, purpose-built hardware routers with built-in redundancy features are still the gold standard for high availability.

5. Can I run other services on a soft router?

Yes, one of the advantages of soft routers is the ability to run other network services and applications on the same hardware. Common examples include firewalls, VPN servers, DNS and DHCP servers, and network monitoring tools. However, be careful not to overload the router with too many services, which could impact its routing performance. It’s a good idea to monitor resource usage and offload services to other servers if needed.

Conclusion

Soft routers are a powerful and flexible alternative to traditional hardware routers in many scenarios. Their software-based nature allows for easy customization, scalability, and integration with other network services. However, they also have limitations in terms of performance, reliability, and feature support compared to dedicated hardware routers.

When deciding whether to use a soft router, consider your specific requirements for bandwidth, packet rate, availability, and features. Soft routers are a great fit for small to medium-sized networks, lab and education environments, and cloud networking. For very high performance and availability needs, hardware routers are still the best choice.

Regardless of the scale of your deployment, understanding the principles and trade-offs of soft routing is valuable knowledge for any network professional in today’s software-defined networking landscape. Hopefully this guide has given you a solid foundation to start exploring and implementing soft routers in your own projects. Happy routing!