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Networking Fundamentals · Foundational

Ephemeral Ports

Short-lived client-side source ports assigned by the operating system for outgoing connections, typically 49152-65535.

Definition

IANA defines 49152-65535 as the dynamic or private range, and Windows uses it by default, while many Linux systems use 32768-60999. Each outbound connection gets a unique ephemeral port so return traffic reaches the right process. Firewalls must allow return traffic to these ports, which stateful inspection handles automatically.

Example

A browser opening three connections to one server uses three different ephemeral source ports.

Exam tip

The server's port is fixed and well known; the client's source port is random and ephemeral.

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