1. Border Gateway Protocol (BGP) Moving Data… Lighting Solutions 800.903.8906 http://www.citynet.net sales@citynet.net

2. BGP • What • Why • Who • When • Where

3. BGP Version 4 • RFC 1771 • Intelligent route selection based on most specific prefix and shortest Autonomous System (AS) path • Classless Inter Domain Routing (CIDR) • Current Internet standard for inter-domain (AS) exterior routing

4. Border Gateway Protocol (BGP) • Used for carrying routing information between AS’s • Path vector protocol • Incremental • Runs over TCP (port 179) • Conveys information about AS path topology

5. General Operation • Learns multiple paths via internal and external BGP speakers • Picks the best path and installs in the IP forwarding table • Policies applied by influencing the best path selection

6. When should I use BGP? • Dual- or multi-homed • Providing partial or full internet routing to a downstream customer • Anytime the AS path information is required

7. BGP is not needed… • … if singularly homed • … if not providing downstream routing • Use a default route!

8. Load Balancing • BGP itself does not load-balance traffic; it chooses & installs a “best” route.

9. BGP Load Balancing Problem • “Since BGP picks a ‘best’ route based upon most specific prefix and shortest AS_PATH, it becomes non-trivial to figure out how to manually direct specific portions of internal traffic (prefixes) in a distributed fashion across multiple external gateways.”

11. Asymmetric Routing Paradigm • In the Internet, it is impossible to control end-to-end routing and paths traversed • Packets may not always traverse the same downstream path as they do when forwarded upstream

12. Summary • Use BGP only when needed! • IGP and conventional BGP network problems • BGP gives flexibility and control