BGP Techniques (Practical & Real-World)

BGP Techniques (Practical & Real-World)

🔹 1. Path Selection Control

Used to influence which route BGP prefers.

• Weight (Cisco-specific, highest wins)
• Local Preference (higher preferred inside AS)
• AS Path Prepending (make paths less attractive)
• MED (lower preferred between ASes)
• Origin type (IGP > EGP > Incomplete)

📌 Most commonly used: Local Preference (inbound), AS Path Prepending (outbound)

🔹 2. Route Filtering

Control which routes are advertised or accepted.

• Prefix lists (preferred over ACLs)
• Route maps for advanced filtering
• Max-prefix limits to prevent route floods

📌 Prevents route leaks and improves stability.

🔹 3. Traffic Engineering

Steer traffic for performance or cost control.

• Inbound traffic: AS Path prepending, MED
• Outbound traffic: Local Preference, Weight
• Multi-homed optimization

🔹 4. BGP Peering Types

• eBGP – Between different AS numbers
• iBGP – Within the same AS
• Route Reflectors – Reduce iBGP full-mesh
• Confederations – Scale large networks

🔹 5. BGP Stability & Convergence

Improve reliability and reduce flapping.

• Route dampening
• BFD for fast failure detection
• Graceful restart
• Keepalive & hold timers tuning

🔹 6. Security Techniques

Protect BGP sessions and routing information.

• MD5 authentication
• Prefix filtering (anti-route leak)
• TTL security (GTSM)
• RPKI (route origin validation)

🔹 7. Scalability Techniques

• Aggregation (route summarization)
• Communities for policy control
• Selective route advertisement
• Default route injection