BGP uses a path-vector algorithm to exchange routing information between ASNs. In this manner, each BGP router determines its own loop-free, best path toward a particular destination.
The loop-free mechanism is achieved because BGP routers won’t accept routes with an AS-Path with it’s own AS in the path attribute.
BGP shares routes only with neighbors that are explicitly defined, after a TCP connection has been established. Updates are sent to neighbors only when changes to the route table are detected; there are no periodic routing updates.
An administrator can influence path selection by altering BGP attributes, because sometimes it is warranted to choose a sub-optimal route. These reasons may include avoiding a transit AS, or avoiding a slow or congested link.
Stuck-in-Active: Journal of an IT-Network Administrator 