Enterprise Routing and Switching, Specialist (JNCIS-ENT) JN0-352 Exam Questions with Experts Answers Updated Recently

Local preference is a well-known, discretionary BGP path attribute carried exclusively in IBGP UPDATE messages, and Junos assigns every route a local preference value of 100 by default whenever a route is received without an explicit LOCAL_PREF value already attached, or when the attribute has not been otherwise modified through routing policy. This default of 100 becomes the implicit baseline against which any administrator-configured local preference adjustments are compared. Because higher local preference values are always preferred over lower ones during BGP best-path selection — and this evaluation happens before AS path length, origin, or MED are ever considered — network engineers commonly use local preference specifically to steer outbound traffic leaving the autonomous system toward a preferred exit peer or upstream provider, by assigning a higher local preference to routes learned from that preferred peer relative to routes learned from alternative peers, making the third statement correct as well. Local preference is explicitly excluded from advertisement to EBGP peers under the BGP specification; it is meaningful only within the boundaries of a single AS and is stripped before a route crosses an AS boundary outward, since a neighboring AS has no reason to trust or honor another organization's internal preference values. A local preference of 0 does not have any special 'drop' semantics in BGP — it is simply the lowest possible numeric preference value and is treated like any other value during comparison, not as a discard instruction. Reference topics: Junos Enterprise Routing – BGP, Local Preference Defaults and Outbound Traffic Engineering.