Anycast vs Unicast vs Multicast: Traffic Routing Explained

How traffic moves across a network is determined by its routing model. Unicast, multicast, and anycast each define how packets are delivered from source to destination.

Choosing the correct routing approach directly affects performance, scalability, fault tolerance, and operational complexity.

This article explains how unicast, multicast, and anycast work, where each excels, and how they are used in real-world infrastructure.

1. Unicast: One-to-One Communication

Unicast is the most common traffic model on IP networks. A single source sends packets to a single destination.

Web browsing, API calls, SSH connections, and database queries all rely on unicast communication.

2. Strengths and Limits of Unicast

Unicast is simple, predictable, and easy to secure. However, it does not scale efficiently for one-to-many delivery.

• Each client requires a separate connection
• Bandwidth usage increases linearly with users
• Server load grows quickly at scale

3. Multicast: One-to-Many Delivery

Multicast allows a source to send traffic to multiple receivers using a single transmission.

Network devices replicate packets only where necessary, significantly reducing bandwidth usage.

4. Common Multicast Use Cases

• Live video and IPTV streaming
• Financial market data distribution
• Routing protocol communication

Despite its efficiency, multicast is complex to manage and rarely exposed to the public Internet.

5. Anycast: One-to-Nearest Destination

Anycast allows multiple servers to share the same IP address. Routing protocols direct traffic to the closest or best available instance.

This model is widely used to improve performance, reduce latency, and increase resilience.

6. Where Anycast Is Used

• DNS root and resolver infrastructure
• Content delivery networks (CDNs)
• DDoS mitigation and edge services

Anycast enables global services to scale horizontally while remaining simple for clients.

7. Comparing the Three Models

Each routing model serves a different architectural goal:

• Unicast: Precision and simplicity
• Multicast: Efficient group delivery
• Anycast: Performance and redundancy

Final Thoughts

Modern networks rarely rely on a single routing model. Instead, they combine unicast, multicast, and anycast to meet different performance and scaling requirements.

Understanding these models is essential for designing reliable, high-performance networked systems.