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networkingNODE: #layer-3-network

OSI Layer 3: Network Layer

The OSI layer responsible for logical addressing (IP), path determination, packet forwarding, and inter-network routing.

AKA:Layer 3, L3, Network Layer, Routing Layer
#networking#osi-layers#ip#routing#packets#icmp
GRAPH_RELATIONS // CONNECTED_NODESLINKED
PART OF:
↳Open Systems Interconnection (OSI) Model
RELATED TO:
↳OSI Layer 4: Transport Layer↳OSI Layer 2: Data Link Layer

OSI Layer 3: Network Layer

Definition

The Network Layer provides functional and procedural means of transferring variable-length data sequences (called Packets) from a source host on one network to a destination host on a different network across multiple intermediary nodes (routers).

Key Functions

  1. Logical Addressing: Assigns unique global addresses (IPv4 / IPv6) to network interfaces to identify hosts across distinct subnets.
  2. Routing & Path Determination: Determines the optimal path from source to destination across multiple hops using routing algorithms (OSPF, BGP, RIP, EIGRP).
  3. Packet Forwarding: Switching packets from an incoming interface to an outgoing interface based on routing tables.
  4. Packet Fragmentation & Reassembly: Splitting packets if they exceed the Maximum Transmission Unit (MTU) of an underlying link.
  5. Quality of Service (QoS) & Congestion Control: Marking packets (DSCP/ToS) for prioritized queuing.

Common Protocols & Devices

  • IPv4 / IPv6: Core internet protocol logical addressing.
  • ICMP (Internet Control Message Protocol): Diagnostic and error reporting (e.g., ping, traceroute, unreachable messages).
  • IPsec: Network layer encryption and VPN tunneling.
  • BGP / OSPF / EIGRP: Routing protocols.
  • Hardware: Routers, Layer 3 Multilayer Switches.

Protocol Data Unit (PDU)

  • Packet

Adjacent Layers

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