A regional bank is dual-homed to ISP-A as primary and ISP-B as backup with two border routers sharing iBGP. Outbound traffic from all internal sites must prefer ISP-A, while inbound Internet traffic should also prefer ISP-A without affecting internal router decisions. Which BGP path-preference attribute design best meets both requirements?

Local preference is carried in iBGP throughout the autonomous system and is evaluated early for outbound best-path selection, so setting it higher on ISP-A routes makes every internal router prefer ISP-A egress without per-router weight tuning; AS-path prepending lengthens the AS-path advertised to ISP-B, making that path less attractive to remote Internet ASes for inbound return traffic while leaving local outbound policy unchanged. Configuring higher weight fails because weight is Cisco-local to a single router and is not advertised even via iBGP, so it cannot provide consistent enterprise-wide outbound preference and has zero effect on inbound Internet decisions. Using MED to steer outbound traffic reverses its direction because MED is advertised to neighbors to influence their inbound decision and is typically compared only between parallel links to the same neighboring AS, not across different ISPs that often reset it. Prepending toward ISP-A and lowering local preference on ISP-B achieves the opposite policy by depreferring the intended primary inbound and outbound paths, and internal prepending does not propagate usefully for Internet inbound control. Exam caveat: remember weight beats local preference locally but does not scale, and MED versus AS-path scope is a favorite discriminator. Practical check: verify with show ip bgp that localpref is consistent internally and that looking-glass views show longer AS-path via backup.