BGP communities are powerful attributes in Border Gateway Protocol (BGP) that allow network operators to tag routes with specific values, enabling granular control over routing policies. Think of them as labels attached to routes that carry additional information about how these routes should be handled across networks.

The Fundamentals of BGP Communities

At their core, BGP communities are 32-bit values, typically written in the format AS:VALUE (such as 65534:100). These values can convey various meanings, from geographic location to desired routing policies. For instance, a community might indicate that a route originated from London or that it should be prepended three times when advertised to specific peers.

Types of BGP Communities

Standard Communities

The traditional 32-bit format allows for basic route tagging and policy implementation. These communities follow the AS:VALUE format and are widely supported across all network equipment.

Extended Communities

These provide additional flexibility with a larger value space and specific types like route targets for MPLS VPNs. They’re particularly useful in more complex networking scenarios where standard communities might prove limiting.

Large Communities

The newest addition to the family, large communities (RFC 8092) offer a 96-bit format (AS:FUNCTION:PARAMETER), providing significantly more flexibility for modern networking needs.

Real-world Application: Exascale IP Transit’s Community Framework

Exascale IP Transit exemplifies the powerful implementation of BGP communities in modern networking. Their extensive community framework provides customers with remarkable control over their routing policies. Some notable capabilities include:

• Geographic-based route control
• AS path prepending at specific locations
• Traffic engineering through selective route announcements
• Blackholing for DDoS mitigation

For instance, if you’re an Exascale customer wanting to reduce traffic through their Amsterdam point of presence (PoP), you can simply apply the appropriate community to your routes, and the network will adjust its routing behaviour accordingly.

Common Use Cases

Traffic Engineering

Network operators can use communities to:

• Influence path selection across different regions
• Implement load balancing across multiple links
• Control route propagation to specific peers or regions

Security Implementation

Communities play a crucial role in network security:

• Implementing RTBH (Remote Triggered Black Hole) filtering
• Managing route visibility across different security zones
• Controlling route propagation for DDoS mitigation

Regional Traffic Management

Operators can use communities to:

• Keep traffic local within specific regions
• Optimise latency by controlling route advertisements
• Implement geographic redundancy policies

Best Practices

When implementing BGP communities, consider these essential practices:

1. Document your community values thoroughly
2. Implement strict filtering on accepted communities
3. Use consistent naming conventions across your network
4. Regularly audit community usage and clean up unused values
5. Consider using large communities for new implementations

The Future of BGP Communities

As networks grow more complex and automation becomes increasingly important, BGP communities continue to evolve. The adoption of large communities and the integration with software-defined networking (SDN) platforms demonstrate how this technology adapts to modern networking requirements.

Conclusion

BGP communities remain a fundamental tool in the network operator’s arsenal, providing the flexibility and control needed in today’s complex networking environments. Whether you’re managing a small network or operating at scale like Exascale IP Transit, understanding and effectively implementing BGP communities can significantly enhance your network’s capabilities and manageability.

Remember, while communities offer powerful control over routing behaviour, they should be implemented thoughtfully with proper documentation and regular auditing to maintain a clean and efficient routing infrastructure.