OSI Layer 3 – Network
Layer 3 is the Network layer.
- responsible for moving data around a network of networks (internetwork)
- moves information around an internetwork using logical network and host IDs
- networks are often heterogeneous
- use a variety of physical layer media and data link protocols
- main appliance at layer 3 is the router
- each packet is given a destination network address
- packet is forwarded router by router (hop by hop) to the target network
- then the hardware address is used to deliver the packet to the target node
Info
- PDUs at the Network layer are called packets or datagrams
- messages at the Data Link layer are called frames
- But, packet is used often for PDUs at any layer
Devices Operating at the Network Layer
- Firewall — filters traffic between networks enforced by an access control list (ACL)