Networking • Routing
BGP & Routing Basics: Understanding Internet Traffic Flow
The Border Gateway Protocol (BGP) is the protocol that routes traffic between autonomous systems (AS) on the internet. Understanding BGP is essential for network engineers and security-focused professionals.
What is BGP?
BGP is a standardized exterior gateway protocol used to exchange routing information across the internet. Each network operator controls an autonomous system with a unique AS number.
- Defines paths between networks
- Ensures loop-free routing
- Supports policy-based route selection
Key Concepts
- Autonomous System (AS): a collection of IP networks under one administrative domain
- Route Advertisement: a network announces the IP prefixes it can reach
- Next Hop: the IP address where traffic is sent to reach a destination
- Path Selection: BGP chooses routes based on policy, path length, and other attributes
Common Use Cases
- Interconnecting data centers
- Multi-homed internet connections
- Traffic engineering and redundancy
Basic Troubleshooting Tips
- Check BGP session status with
show ip bgp summary - Verify route advertisements and prefixes
- Monitor for route flaps and AS path changes
