BGP Best External is used in Active Standby BGP Topologies generally but not limited with that.BGP Best External feature helps BGP to converge much faster by sending external BGP prefixes which wouldn’t normally be sent if they are not overall BGP best path.
There are BGP best internal, BGP best external and BGP Overall best path.
BGP Best external in an active-standby scenarios can be used in MPLS VPN, Internet Business Customers, EBGP Peering Scenarios, Hierarchical large scale Service Provider backbone and many others.
But,How active-standby scenario connection with BGP is created ? In which situation people use active-standby instead of active-active connection ?
Let’s start with the below scenario.
Figure -1 BGP Active-Standby Path Selection Example