Distributed Systems for Practitioners/

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The Network Layer

The Network Layer

Learn about the network layer, the protocols it follows, and the limitations it encounters.

We'll cover the following...

While the link layer is responsible for transferring packets between nodes that are directly linked, the network layer transfers packets between nodes that are not directly linked and might belong to different networks.

Functionalities that help to provide network layer service

The functionalities that help the network layer transfer packets between nodes, which are not directly linked and may belong to different networks, can be divided into two main areas: the control plane and the data plane.

Control plane

The control plane is the part of the network layer that gathers all the necessary meta-information, which is needed to route data packets between nodes.

Data plane

The data plane is the part of the network layer that routes data packets between nodes, while leveraging information provided by the control plane.

Protocols

Note: There are many different protocols that are followed inside the network layer, but it is impractical to cover them all in this lesson. Hence, we will focus on the most central ones in this course.

Every network interface comes with a MAC address, which is used to address the frames at the link layer. However, this address is assigned statically and is not hierarchical, which makes it unsuitable for routing packets in a network. As a result, the network layer introduces a second form of address, called the IP (Internet Protocol) address.

Internet protocol

The IP addresses are assigned statically, either by an administrator or dynamically by the network.

IP addresses are also hierarchical, which means that each address is part of a network that can contain multiple addresses and where the network can also be part of a larger network.

The IP protocol evolved with time to address user needs, and the structure of IP addresses changed along with it. The resultant changes are:

  • An IP v4 address is a 32-bit number.
  • An IP v6 address is a 128-bit number.

Note: The adoption of IP v6 is an ongoing process. Therefore, we will give examples using IP v4. We will refer to it as IP for the sake of brevity.

Structure

IP addresses are represented with dot-decimal notation, consisting of four decimal numbers that represent 8 bits and a ...