This notification-only value carried in packet-mirroring traps is the unique identifier (UID) of the secure policy governing a CLI-trigger-based mirroring configuration, complementing the human-readable juniPacketMirrorPolicyName. An admin uses this stable numeric ID when correlating trap data with the router's internal policy database, since names could theoretically be reused over time. For example, matching juniPacketMirrorPolicyId across multiple traps confirms they all pertain to the exact same underlying secure policy even if its name were later changed.