Trisul's Blog

If you’ve ever wondered how your data finds its way across the globe, the answer is BGP—the Border Gateway Protocol. After years of working with ISPs and enterprise networks, I can tell you: understanding BGP is essential for any network professional.

What is BGP?

BGP is the protocol that routes data between autonomous systems (AS)—the big networks that make up the internet. It’s how ISPs, data centers, and large organizations exchange routing information and choose the best path for your traffic.

Why BGP Matters

• Global Routing: BGP decides which path your packets take across the world.
• Redundancy: Allows for multiple connections to the internet, improving reliability.
• Traffic Engineering: Lets you control inbound and outbound routes for performance or cost.
• Security: Misconfigured or hijacked BGP routes can cause outages or security breaches.

How BGP Works: The Basics

• Routers running BGP establish peerings with other routers (neighbors).
• They exchange routing tables—lists of which networks they know how to reach.
• BGP uses attributes (AS path, local preference, MED) to select the best route.

Sample: Configuring BGP on Cisco IOS

router bgp 65001
 bgp log-neighbor-changes
 neighbor 203.0.113.1 remote-as 65002
 network 192.0.2.0 mask 255.255.255.0

BGP Best Practices

• Always filter routes—never accept or advertise everything by default.
• Use prefix lists and route maps to control what you send and receive.
• Monitor BGP sessions and logs for instability or hijacks.
• Document your AS numbers, peerings, and policies.

Conclusion

BGP is the glue that holds the internet together. Understanding its basics—and its risks—will make you a better network engineer and help you build more resilient, secure networks.

Want to dive deeper into BGP or need help with multi-homing? Reach out for expert advice!