Understanding BGP Basics

BGP Fundamentals

BGP (Border Gateway Protocol) is a standardized exterior gateway protocol designed for routing across administrative domains. It serves as the primary routing protocol of the Internet.

Key BGP concepts:

  • Path Vector Protocol: BGP tracks the sequence of Autonomous Systems (ASes) that routes traverse, using this information for routing decisions.

  • Autonomous Systems: Networks managed by a single entity under a common routing policy. Each AS has a unique Autonomous System Number (ASN).

  • BGP Peers: BGP routers establish TCP-based connections with other BGP routers to exchange routing information.

BGP Use Cases in OpenStack

Red Hat OpenStack Platform specifically supports ML2/OVN dynamic routing with BGP in both control and data planes. In this environment, BGP enables:

  1. Control Plane High Availability: Advertises control plane Virtual IPs to external routers, directing traffic to OpenStack services.

  2. External Connectivity: Connects OpenStack workloads to external networks by advertising routes to floating IPs and provider network IPs.

  3. Multi-cloud Connectivity: Links multiple OpenStack clouds together through route advertisement.

  4. High Availability: Provides redundancy by rerouting traffic during network failures.

  5. Subnet Failover: Enables failover of entire subnets for public provider IPs or floating IPs from one site to another.

Benefits of Dynamic Routing with BGP

BGP offers significant advantages for OpenStack environments:

  • Scalability: New networks and floating IPs can be routed without manual configuration.

  • Load Balancing: Supports equal-cost multi-path routing (ECMP) to distribute traffic efficiently.

  • Redundancy: Automatically reroutes traffic during network failures, critical for controllers deployed across multiple availability zones.

  • Interoperability: Works with diverse networking equipment and cloud platforms.

  • Simplified L3 Architecture: Enables pure Layer 3 data centers, avoiding Layer 2 issues like large failure domains, broadcast traffic, and slow convergence.

  • Distributed Network Architecture: Distributes L2 provider VLANs and floating IP subnets across L3 boundaries with no requirement to span VLANs across racks (for non-overlapping CIDRs).

  • Improved Data Plane Management: Provides better control and management of data plane traffic.

  • Next-Generation Fabric Support: Enables integration with next-generation data center and hyperscale fabric technologies.