BGP.KMCD.DEV

Global Routing Telemetry

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Understanding BGP

The Border Gateway Protocol (BGP) is the routing protocol of the internet. It acts like the postal service for the web, allowing different networks (Autonomous Systems or ASes) to announce which IP addresses they control and discover the most efficient paths to send data to each other. Because BGP relies on trust, it is vulnerable to misconfigurations or malicious attacks known as Route Hijacks.

1. Announcing

The Origin AS 'announces' its IP space. Routers propagate this information so that every network knows the path back to the origin.

UserOrigin AS

2. Routing

Data follows the established paths. BGP selects the shortest route to reach the destination AS.

UserDestination

3. Withdrawals

When a prefix is no longer reachable, a 'withdrawal' message is sent. If an origin AS goes dark, its upstream peers detect the lost session and propagate the withdrawal to the rest of the internet.

UserOrigin

4. Asymmetric Routing

In BGP, the path taken to reach a destination may differ from the path taken for return traffic. This is normal but can complicate troubleshooting.

UserDestination

5. Multipath (ECMP)

Equal-Cost Multi-Path (ECMP) allows a router to distribute traffic across multiple best-paths simultaneously for better load balancing.

UserDestination

6. Anycast Routing

Multiple servers announce the exact same IP address. BGP naturally routes user traffic to the topologically closest destination, enabling global CDNs and root DNS.

Global Transit (Longer Path)User (EU)User (Asia)Origin (1.1.1.1)Origin (1.1.1.1)

Reference & Standards

Advanced BGP Topics

Explore the complex protocols and architectural standards built on top of BGP's extensible framework.

Path & Scalability

  • Route Reflection (RFC 4456)

    Eliminates the need for a full iBGP mesh by using reflectors to propagate internal routes.

  • BGP ADD-PATH (RFC 7911)

    Allows advertising multiple paths for the same prefix to enable better ECMP and faster convergence.

  • BGP PIC

    Prefix Independent Convergence allows millisecond failover by using pre-calculated backup paths.

  • Confederations (RFC 5065)

    Dividing a large AS into smaller sub-ASs to simplify management and reduce peering overhead.

Security & Integrity

  • BGPsec (RFC 8205)

    Full path signing. Rarely deployed due to high CPU load; RPKI is the preferred modern alternative.

  • BGP OPSEC (RFC 7454)

    Best practices for securing BGP sessions including TTL security and prefix filtering.

  • RPKI Validation

    Cryptographic verification that an AS is authorized to originate specific IP prefixes.

Traffic Engineering & Resiliency

Modern Overlays