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Networking Fundamentals · Foundational

Decapsulation

The reverse of encapsulation, in which each layer on the receiver removes and processes its header before passing data up.

Definition

As a frame arrives, the Data Link layer checks the FCS and strips the frame header and trailer, the Network layer reads and removes the IP header, the Transport layer reassembles segments and delivers data to the correct port. Each layer acts only on information meant for its peer layer. Routers decapsulate up to Layer 3 and re-encapsulate in a new frame for each hop.

Example

A router removes the incoming Ethernet header, reads the IP header, and builds a new frame for the outgoing interface.

Exam tip

Routers rewrite the Layer 2 header at every hop while the IP source and destination stay the same (absent NAT).

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