The protocol that holds the internet together.
WHAT IT DOES
Exchanges reachability information between autonomous systems.
WHAT IT ADVERTISES
Address prefixes, and the path of autonomous systems to reach them.
WHAT MAKES IT UNUSUAL
It selects paths by policy, not by measured performance.
WHAT THAT MEANS
BGP does not know or care which path is faster.
WHAT INFLUENCES PATH SELECTION
Local preference, set by you, which dominates Path length, counted in autonomous systems Origin and other attributes Multi-exit discriminators, suggesting a preference to a neighbour
WHAT LOCAL PREFERENCE CONTROLS
Which way traffic leaves your network.
WHAT PATH PREPENDING DOES
Makes a path appear longer, discouraging its use.
WHAT THAT CONTROLS
Which way traffic arrives, imperfectly.
WHY IMPERFECTLY
You influence, but do not control, what other networks choose.
WHAT TO UNDERSTAND
Outbound traffic is yours to control; inbound is a matter of influence.
WHAT IT REQUIRES TO RUN
Your own address space, an autonomous system number, and at least two providers.
WHAT IT PROVIDES
Provider independence, and failover between them.
