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Networking Fundamentals · Foundational

Packet

The Layer 3 PDU, consisting of an IP header plus a transport-layer payload.

Definition

A packet contains source and destination IP addresses, a TTL or hop limit, a protocol identifier and other control fields, followed by the encapsulated segment or datagram. Routers forward packets hop by hop based on the destination IP address. The term is also used loosely for any unit of network data.

Example

A ping sends ICMP echo request packets to the destination IP address.

Exam tip

In strict PDU terminology, "packet" belongs to Layer 3; use "frame" for Layer 2 and "segment" for TCP.

Related terms