Which of the following is NOT considered an option of import policies?

BGP import policies are applied to routing updates received from a BGP peer. Their primary functions are to filter which routes are accepted into the local BGP RIB (Routing Information Base) and to modify attributes to influence the local Autonomous System's (AS) path selection. Setting the Multi-Exit Discriminator (MED) value is an action performed on routes being advertised to an external peer to influence that peer's routing decisions. Therefore, setting the MED is a function of an export policy, not an import policy.

A. Preventing unwanted NLRI (Network Layer Reachability Information) from entering the AS is a fundamental purpose of an import policy, acting as a security and stability filter.
B. Filtering NLRI using criteria like AS Path or prefix-lists is the specific mechanism by which an import policy decides which routes to accept or reject.
C. Modifying the Local Preference attribute on incoming routes is a common import policy action used to influence the preferred exit point from the local AS.

1. Nokia 7750 SR OS Router Configuration Guide, Release 22.10.R1, Section: "Route Policies", Subsection: "Route Policy Action Statements".

The documentation specifies that the metric (MED) action "sets the MED attribute for routes advertised to a BGP peer." This confirms it is an export policy action.

Conversely, the local-preference action is described as being applied to accepted routes to influence path selection within the local AS, which is a typical import policy function.

2. RFC 4271 - A Border Gateway Protocol 4 (BGP-4), Section 5.1.3: "MULTIEXITDISC".

The RFC states, "This attribute MAY be used on external (inter-AS) links to discriminate among multiple exit or entry points to the same neighboring AS." This implies the attribute is set by the advertising router (in an export policy) to influence the receiving router.

3. RFC 4271 - A Border Gateway Protocol 4 (BGP-4), Section 5.1.5: "LOCALPREF".

The RFC describes LOCALPREF as an attribute used "to inform other BGP speakers in the receiver's own autonomous system of the sending speaker's degree of preference for an advertised route." This confirms it is set upon receipt of a route (in an import policy) for internal use.