Single-Session DoS Attack
A single-session DoS attack typically will not trigger Zone or DoS Protection profiles because they are attacks that are formed after the session is created. These attacks are allowed by the Security policy because a session is allowed to be created, and after the session is created, the attack drives up the packet volume and takes down the target device.
Configure DoS Protection Against Flooding of New Sessions to protect against flooding of new sessions (single-session and multiple-session flooding). In the event of a single-session attack that is underway, additionally Use the CLI to End a Single Attacking Session.

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