layer 3 of osi model is network layer, network layer manages device addressing, tracks the location on the network, and determines the best way to move data, which means that the Network layer must transport traffic between devices that aren't locally attached.Routed protocols such as IP are used to determine logical addressing, which can identify the destination of a packet or datagram. The most common network device found at the Network layer is a router; however, Layer 3 switches may also be implemented.
A router at the Network layer follows these general steps to ensure proper data transport:
- The router checks the destination IP address of the incoming packet on the router interface.
- Packets destined for that router are processed, whereas packets destined for another router must be looked up in the routing table.
- The router determines an exit interface based on the routing table and sends the packet to the interface for framing and forwarding. If there is no route in the routing table, the packet is dropped by the router.
types packet are used at the Network layer:
- data packets : used to transport user data through the internetwork. Protocols used to support data traffic are called routed protocols; example of routed protocols are IP and IPv6.
- route update packets : used to update neighboring about the networks connected to all routers within the internetwork. protocols that send route update packets are called routing protocols(RIP, RIPv2, EIGRP, and OSPF). Route update packets are used to help build and maintain routing tables on each other.
A routing table on a router contains the following information:
- Network Address
- Interface --: Exit interface used to forward packets
- Metric --: Distance to reach a remote network
Layer 3 routed protocols include the following:
- Internet Protocol (IP)
- Internet Packet Exchange (IPX) --: Part of the IPX/SPX protocol suite created by Novell NetWare
- AppleTalk DDP --: Datagram delivery protocol used by Apple
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