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Networking Fundamentals · Foundational

Network Layer (L3)

OSI Layer 3, which provides logical addressing and routing of packets between different networks.

Definition

The Network layer handles end-to-end logical addressing (IPv4 and IPv6), path selection and packet forwarding across multiple hops. Its PDU is the packet. Routers and multilayer switches operate at Layer 3, and protocols here include IP, ICMP and IPsec.

Example

A router reads the destination IP address of a packet and forwards it toward the next hop.

Exam tip

ICMP is a Layer 3 protocol even though it rides inside IP, so ping tests reachability at the Network layer.

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