Routing

Internet Routing Architecture

BGP (Border Gateway Protocol)

The protocol of the internet. It exchanges reachability information between Autonomous Systems (AS). What is BGP? (Cloudflare).

• ASN (Autonomous System Number): Unique identifier for a network (e.g., Cloudflare is AS13335).
• Peering: Direct interconnection between two networks to exchange traffic (settlement-free).
• Transit: Paying an upstream provider to carry traffic to the rest of the internet.
• Path Selection: BGP prefers the shortest AS_PATH, but policies (Local Pref, MED) often override this for business/performance reasons.

Anycast Routing

A network addressing and routing methodology where a single destination address has multiple routing paths to two or more endpoint destinations. What is Anycast? (Cloudflare).

• Mechanism: The same IP prefix is advertised via BGP from multiple geographic locations (PoPs).
• Result: The internet routing infrastructure (BGP) automatically directs traffic to the “topologically closest” location.
• Cloudflare Context: All Cloudflare services run on Anycast IPs. A user in London hits the London data center; a user in Sydney hits Sydney.
• Benefits:
  • Latency: Minimized RTT.
  • DDoS Mitigation: Attack traffic is distributed across the global network surface, preventing any single PoP from being overwhelmed.