What Is BGP? Border Gateway Protocol

BGP (Border Gateway Protocol, RFC 4271) is the Internet's routing protocol, connecting the world's 100,000+ autonomous systems (AS). It is a policy-based path-vector protocol and the only technology capable of handling 950,000+ IPv4 routes. It is critical to the Internet.

Terminology

• AS (Autonomous System): routing domain identified by an ASN
• eBGP: between different ASes
• iBGP: within the same AS (full mesh or RR)
• NLRI: advertised routing information
• Peering: BGP session between 2 routers

Path Attributes (Selection)

• Weight (Cisco-local): higher value preferred
• Local Preference: within the AS
• AS_PATH: shorter path preferred
• Origin: IGP > EGP > Incomplete
• MED: inter-AS
• eBGP > iBGP

Use Cases

• ISP/service provider: full Internet table
• Enterprise multihoming: 2 ISPs
• Data center: eBGP spine-leaf underlay
• Cloud: Azure Virtual WAN, AWS Direct Connect
• Customer MPLS VPNs: VPNv4

Best Practices

• MD5 or TCP-AO authentication
• Max-prefix limits
• Systematic inbound/outbound filtering
• BFD for <1s convergence
• RPKI validation for security

Order from OPTINOC

Enterprise + ISP BGP configuration. Cisco ASR/IOS, Juniper MX, FortiGate. BGP training. Quote within 48 hours.