AS100 and AS200 each have two peering points in different parts of their network. AS100 would like to use one of the links and keep the other link as backup. What should be changed for the design insi

MED is an attribute advertised to external peers to influence how AS200 routes traffic into AS100, not how AS100 itself selects between two exit paths.

Weight is a Cisco-proprietary attribute that is local to a single router and not propagated via iBGP, so it cannot provide consistent path selection across all routers in AS100.

AS-PATH prepending is used to influence external ASes' routing decisions toward you, not to control internal path selection within your own AS.

Local preference is an iBGP attribute applied to routes received from external peers and propagated to all routers within AS100 via iBGP, making it the authoritative tool for choosing which of two peering links AS100 prefers as primary versus backup. A higher local preference value on routes learned via the preferred link causes all routers in AS100 to consistently use that path, while the lower local preference on the backup link keeps it inactive unless the primary fails.