Guide
What Is BGP and Why Does It Matter?
BGP is the routing system that helps networks exchange reachability information on the internet. For organizations with public routing needs, planning matters.
By Austin Hadley, Founder and Chief Executive Officer Published Updated
BGP is the routing system that helps networks exchange reachability information on the internet. For organizations with public routing needs, planning matters.
What BGP does
The Border Gateway Protocol, or BGP, lets independently operated networks exchange information about which IP address prefixes they can reach. Those networks are identified by autonomous system numbers. A BGP router selects paths using policy and route attributes; it does not simply choose the geographically shortest route.
An organization that advertises its own public address space can use BGP to tell upstream providers where that space is reachable. The design must account for what routes are accepted, what prefixes are announced, and how traffic should behave when a connection or provider fails.
- Prefixes describe ranges of IPv4 or IPv6 addresses.
- An autonomous system number identifies the routing domain presenting its own policy.
- Inbound and outbound policies determine which routes are accepted, preferred, and advertised.
When businesses use it
Public BGP is most relevant when an organization has provider-independent address space, connects to more than one internet provider, operates network services from multiple sites, or needs direct control over public route announcements. Many smaller networks do not need to run BGP and are better served by provider-assigned addresses and simpler failover.
Multiple providers can improve resilience, but BGP alone does not make applications highly available. DNS, firewalls, stateful sessions, power, physical paths, and the applications themselves must also tolerate failure. Define the availability goal first, then decide whether public routing is an appropriate part of the solution.
- Clarify whether the goal is address portability, provider diversity, traffic policy, or all three.
- Confirm address-space, autonomous-system, provider, and registry requirements.
- Model application behavior during circuit, router, provider, and site failures.
Common risks
A configuration error can advertise routes that should remain private, accept an unexpectedly large routing table, or send traffic toward the wrong path. Use explicit import and export filters, maximum-prefix limits, controlled change procedures, configuration backups, and monitoring of both sessions and announcements.
Public routing security also depends on coordination outside the router. Keep Internet Routing Registry records and Route Origin Authorizations current where they apply, protect registry and provider accounts, monitor externally visible announcements, and maintain accurate contacts for routing incidents.
- Filter routes by expected prefix and prefix length in both directions.
- Use maximum-prefix limits and alerts to contain unexpected route volume.
- Validate intended announcements from an external vantage point after changes.
Planning questions
Before implementation, document the autonomous system, address space, upstream providers, circuit handoffs, router capacity, accepted route scope, desired inbound and outbound policy, and failure behavior. Decide whether the routers will receive only a default route, a limited set of routes, or full internet tables, because each choice changes capacity and operational requirements.
Create diagrams and a change plan that another qualified operator can follow. Include validation commands, rollback steps, provider escalation contacts, out-of-band access, and maintenance windows. Exercise failure scenarios periodically; an untested backup session may be established yet still fail to carry production traffic correctly.
- Define route policy in writing before translating it into vendor configuration.
- Confirm hardware resources, software support, telemetry, and out-of-band management.
- Test convergence, return paths, application health, and rollback under controlled conditions.