As fibre network operators (FNOs) scale their infrastructure to meet the increasing demand for high-speed broadband, selecting the right network architecture becomes paramount. A well-designed architecture not only ensures efficient packet switching but also reduces outages and operational challenges. A critical aspect of this architecture is how Internet Service Providers (ISPs) are connected to customers, often using dedicated VLANs to route traffic through a regional co-location data centre.

This article explains why switches, rather than routers, are the optimal choice for this architecture and explores the consequences of implementing the wrong approach.

The Core of FNO Architecture

Modern FNOs typically act as Layer 2 carriers, delivering connectivity between customers and ISPs. This setup involves:

Access Network: The fibre network reaching customer premises.
Aggregation Layer: Where customer traffic is aggregated and segmented into VLANs for each ISP.
Backhaul: Connections to regional co-location data centres where ISPs pick up the traffic.

The aggregation layer is critical, as it determines how efficiently customer traffic is routed to ISPs. This is where the choice between switches and routers comes into play.

Why Switches Are Better Than Routers in This Setup

1. Switches Are Designed for High-Volume Packet Switching

Switches excel at moving large volumes of traffic at Layer 2 with minimal latency. They are purpose-built to:

Segment traffic into VLANs.
Handle high-speed forwarding of packets across multiple interfaces.
Support dense port counts and high bandwidth demands.

Routers, on the other hand, operate at Layer 3 and are primarily designed for:

Making complex routing decisions.
Managing smaller traffic volumes.
Enabling WAN connectivity.

For an FNO, where most traffic stays at Layer 2 until it reaches the ISP, switches are the natural choice. Using routers for this purpose is akin to using a race car to plough a field—it’s not designed for the task.

2. Efficiency in VLAN Handling

Switches natively support VLAN tagging and trunking, which are essential for isolating ISP traffic. Features like VLAN pruning and QinQ (stacked VLANs) allow:

Scalability for multiple ISPs.
Efficient use of available bandwidth.
Routers can support VLANs, but their implementation is often limited and less efficient, making them unsuitable for managing hundreds or thousands of VLANs in a fibre network.

3. Cost and Scalability

Switches are more cost-effective than routers for aggregation and backhaul purposes:

Higher port densities at a lower price point.
Lower power consumption and simpler cooling requirements.
Easy scalability by adding more switches to the aggregation layer.

Routers are not built to handle large-scale Layer 2 forwarding, and using them in place of switches leads to unnecessary expense and operational inefficiencies.

Consequences of the Wrong Architecture

1. Increased Outages

When routers are forced into roles they weren’t designed for, they become a single point of failure:

Overloaded CPUs cause processing delays.
Inability to handle large forwarding tables leads to packet drops.
VLAN mismanagement results in incorrect routing of ISP traffic.

2. Bottlenecks in Performance

Routers can introduce latency and throughput limitations, especially when handling tasks like VLAN switching that are outside their core function. These bottlenecks can cascade into network-wide performance issues.

3. Complex Troubleshooting

Misusing routers complicates network troubleshooting. Engineers face challenges in isolating issues, as the network’s architecture does not align with the capabilities of the deployed hardware.

The Role of Regional Co-Location Data Centres

In this architecture, regional co-location data centres serve as the handoff point between the FNO and ISPs. The ideal setup includes:

Switch-Based Aggregation: Switches connect customer VLANs to the ISP’s infrastructure.
Interoperability: Standardised VLAN tagging ensures seamless communication between the FNO and ISP equipment.
Resilience: Redundant links and switches prevent single points of failure.

By leveraging switches at the aggregation layer and reserving routers for core Layer 3 tasks, FNOs can optimise their architecture for reliability and performance.

Best Practices for FNOs

Use Layer 2 Switches for Aggregation
Select high-capacity switches with features like VLAN trunking, QinQ, and redundant power supplies.
Reserve Routers for Core and Edge Functions
Deploy routers only where Layer 3 functionality is essential, such as peering and managing IP routing between regions.
Plan for Redundancy
Ensure the architecture includes failover mechanisms, such as stacked switches or redundant paths, to prevent outages.
Monitor and Optimise
Use network monitoring tools to track performance and detect anomalies in real-time, reducing the risk of cascading failures.

Wrap

The architecture chosen by fibre network operators significantly impacts the performance, reliability, and scalability of their networks. By using switches for Layer 2 aggregation and VLAN management, FNOs can build efficient, resilient networks tailored to the demands of SD-WAN and ISP interconnectivity.

Conversely, forcing routers into switching roles creates bottlenecks, increases the risk of outages, and inflates costs. A clear understanding of the strengths and limitations of each technology ensures the network can meet both current demands and future growth.

✈️Choosing the Right Architecture for Fibre Network Operators | The Case for Switches Over Routers🪂