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Table of Contents Link to heading

Tip
A host refers to a device that is in an IP network and has an IP address.

OSI Network Layer Link to heading

Info
The OSI network layer prepares transport layer segments for routing from one host to another.
Note
  1. Assign logical addresses to devices on the network
  2. Encapsulate the packet with necessary data for delivery
  3. Fragment the packet when it comes across a network that restricts the size of the packet
  4. Route the packet from the source to the destination through the web of connected networks
  5. Have the data decapsulated for processing by the destination host

The network layer receives segments (L4 PDU), which have been processed into a transportable size and numbered for reliability, from the transport layer. It is now up to the network layer to use protocols to add addressing and other information to the PDU and send it (L3 PDU) to the next router along the best route to the destination network.

Addressing Link to heading

Info
Each sending (source) and receiving (destination) host must have a unique network layer address, called an IP/logical address.
Info
Read more at 🔗.

Encapsulation Link to heading

Info
the process of packaging the PDUs sent between networks by filling their IP header with L3 control information, including source and destination IP addresses, and some other bits that identify the PDU as a packet (L3 PDU) so that the network can deliver it to the destination host.

When segments have been encapsulated at the network layer, they are referred to as packets.

Fragmentation Link to heading

Info
the process of a router breaking up a large IP packet into smaller pieces to fit the MTU of the underlying data link layer and the destination network that has media restrictions.

Maximum Transmission Unit (MTU) Link to heading

Info
represents the largest possible L3 packet size (including all headers and the payload) that can be transported by the current data link layer, measured in bytes.

Routing Link to heading

Note
Read at 🔗.

Decapsulation Link to heading

Info
the process of the destination router’s NIC removing the L3 encapsulation data from a packet.

When an IP packet is decapsulated, the network layer reassembles the packets into segments and hands them up to the transport layer.

Network Protocols Link to heading

Info
specify the packet structure and processing used to carry the data from one host to another.

L3 protocols used to be largely proprietary, which limited communication to a manufacturer’s specific equipment. Internet Protocol (IPv4 and IPv6), however, is open source and allows devices from various manufacturers to communicate with each other, which makes itself the most widely used L3 data-carrying protocol.

Common Network ProtocolDescription
Internet Protocol version 4 (IPv4)Most widely used network protocol
Basic protocol of the Internet.
Internet Protocol version 6 (IPv6)Currently in use in some areas
Will work with IPv4 and likely replace it.
Novell IPXPart of Novell NetWare, a widely popular internetworking protocol in the 1980s and 1990s.
AppleTalkApple Computer’s proprietary networking protocol.
Connectionless Network Service (CLNS)A protocol used in telecommunication networks that does not require established circuits.