What Is a BGP Prefix?
A BGP prefix is an IP address block announced by an Autonomous System (ASN) via BGP, indicating that the AS is responsible for routing traffic to those addresses. Prefixes are expressed in CIDR notation (e.g., 8.8.8.0/24) and are the fundamental unit of internet routing.
Cómo Funciona
When a network operator receives an IP address allocation from their RIR, they configure their BGP routers to announce (advertise) those prefixes to their peers. The prefix travels through BGP sessions across the internet, with each AS adding itself to the AS_PATH. Routers worldwide then know to forward traffic destined for addresses in that prefix toward the announcing AS. More specific prefixes (longer prefix length, like /24) override less specific ones (like /16) in routing decisions.
Por Qué Importa
BGP prefix announcements determine how internet traffic reaches your network. Announcing too-specific prefixes (more-specific hijacks) can attract traffic intended for others. Not announcing your prefix means your addresses are unreachable. Monitoring your prefix announcements is essential for network security and visibility.
Problemas Comunes
- Prefix not announced — network unreachable from the internet
- More-specific prefix hijack attracting traffic meant for another AS
- Prefix deaggregation (announcing many /24s instead of one /16) contributing to routing table bloat
- ROA max-length misconfiguration blocking legitimate more-specific announcements