Consider the following example. There are four routers – 2 CE routers in AS 65000 and 2 PE routers in AS 65100 (ISP). We use a route-map on router GW2 to set the BGP metric (MED) – the 6th value in the path selection process – to influence ISP router path selection to use the primary path, as it has a lower MED value (default).
Stuck-in-Active: Journal of an IT-Network Administrator 