This notification-only string carried in packet-mirroring traps identifies the specific trigger value (such as a username or IP address) that caused mirroring to be invoked, with its category identified by the companion juniPacketMirrorTriggerType field. An admin reads this to know exactly which user, address, or session attribute matched the mirroring policy and set off the trap. For example, a juniPacketMirrorTrigger value of "jdoe" alongside juniPacketMirrorTriggerType=username(3) tells the admin the mirroring event was triggered by that specific subscriber's login.