Layer 2 and Layer 3 Switches Research

Layer 2 and Layer 3 Switches Research.

Layer 2 and Layer 3 Switches.

A device that is used to send a data packet in a local network is known as a Switch. A switch is preferred over a hub because a hub floods the network with the pocket and that packet can only be received by destination system. Others will just drop sue to increase in traffic. To solve this problem, a switch was introduced. Just like a hub, a switch will first learn by flooding to fill MAC. A MAC is an address table on which devices are connected. After learning how to fill MAC, the Switch sends packets to a particular host only.

Both layer 2 and layer 3 have been adopted from Open System Interconnect (OSI) model. OSI model is a reference model that is used in explaining and describing network communication. This model contains seven layers including: application, presentation, session, transport, network, data link and physical layer. Layer 3 is in the network layer while layer 2 is in the data link layer.

Traditional switches operate on Layer 2 of the Open System Interconnect (OSI) system, in which packets are sent to specific switch port based on a particular destination MAC addresses. Routing operates on layer 3 where packets are sent to a specific next-hop IP address based on IP destination address. Those devices in layer 2 do not require routing to reach local peers. The only thing required in these devices is a destination MAC address which is resolved via the Address Resolution Protocol. This is illustrated in the figure below.

In this figure, PCA wants to send traffic to PC B at an IP address PC A does not know the unique address but until it discovers it via an ARP that is broadcasted throughout layer 2. It therefore sends packets to the appropriate destination MAC address which later forwards the correct port based on MAC address table. The figure below represents Layer 2 switching:

There exist a broadcast domain within layer 2 environment. Any broadcasting traffic is forwarded to all ports exempting the port the broadcast packet arrived on. Domains contained in large Layer 2 broadcasts are susceptible to certain problems that are unintended. Such problems include the broadcast storm, the storms have the ability to cause network outage. For security and policy reasons, it’s important to separate certain clients into different domains of broadcast.

Layer 2 switch has the ability to assign VLANs to switch ports. These VLANs have different Layer 3 subnets and hence different broadcast domain. They allow for more flexibility by allowing layer 3 networks to share same layer 2 infrastructure. VLANs exist on their own layer 3 subnet and hence their routing need to occur for traffic to in between VLANs.

Differences between layer 2 and layer 3

The major difference between the two revolves around their routing functions. While layer 2 works on MAC address and doesn’t care about IP addresses, layer 3 concentrates more on the IP addresses. Layer 3 switches can perform all functions of a layer 2 switch, it does both static and dynamic routing. This means that layer 3 switch handles inter-VLAN communication, IP routing table and has MAC address table too. Switches that add static routing only are also known as Layer 2­­+ or Layer 3 Elite. Layer 3 switches have increased security and power.

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