Border Gateway Protocol (BGP) is the routing protocol that holds the internet together, and understanding it is critical for data center operators who need reliable multi-homed connectivity. BGP allows organizations to announce their own IP address space through multiple upstream providers, providing redundancy and traffic engineering capabilities.
BGP Multihoming Fundamentals
To implement BGP multihoming, you need your own Autonomous System Number (ASN) and a provider-independent IP address block, typically at least a /24 for IPv4. Each upstream provider establishes a BGP peering session with your border routers, through which you advertise your prefixes and receive their routing tables.
Route filtering is essential for safe BGP operation. Configure prefix lists and route maps to control which routes you accept and advertise. Use AS-path prepending to influence inbound traffic distribution across your upstream links, making one provider preferred over another for specific prefixes.
Implement BGP communities to tag routes and simplify policy management. Monitor your BGP sessions with tools like bgpmon or RIPE RIS to detect route leaks and hijacks. Regular testing of failover scenarios ensures that traffic reroutes correctly when a provider link goes down.