Differences Between Layer 2 and Layer 3 Switches

Layer 2 vs Layer 3 Switches

Network switch is a device, which connects end stations or end users at data link layer level. Switches came to market as an intelligent solution for network hubs, which provide high-speed networking facilities. At layer 2 level, switches communicate using Media Access Control (MAC) address, and it provides same functionalities of a multiport bridge. It can be seen as a full-duplex version of the hub. Ethernet switches can dynamically learn the MAC address attached to various switch ports by looking at the source MAC address on frames coming in to a port. As an example, if switch port Fa 0/1 receives a frame with source MAC address aaaa.aaaa.aaaa , the switch can recognize that the MAC address has come from the port Fa 0/1, and if a frame arrives to the switch, to direct to the same MAC address the switch will forward it to Fa 0/1 port.

Layer 2 Switch

Inside switches, VLANS are created to divide a switch in to smaller broadcast domains where we can assign different ports for different subnets. Switches use VLANs to control broadcast, multicasts, unicast, and unknown unicast with layer 2 devices. Different traffics like HTTP, FTP ,SNMP can be efficiently handled from a layer 2 switch. When it comes to network security, layer 2 switches provide simple but strong security facilities like port security. At layer 2 level, techniques like STP are used to keep redundancy inside a network while preventing loops. In network design, layer 2 switches are mostly used at access layer level. In inter VLAN routing between layer 2 switches, we have to use a router, which provides layer 3 facilities.

Layer 3 Switch

To overcome a lot of boundaries like broadcast overload and lack of multiple links, layer 3 switches like cisco Catalyst 3550, 3560, 3750, 4500, 6500 series were introduced, which implement packet forwarding logic of a router in hardware. Layer 3 switches provide both data link layer and network layer facilities within the same device, which will reduce the cost of buying another router to get layer 3 facilities. At the same time, converting a layer 2 port in to a layer 3 port is useful when one port is available. Routing protocol like EIGRP, and sometimes, OSPF can be used to route a routed port where we assigned an IP address after disabling the layer 2 functions of a port using “no switchport” command. Layer 3 switches are mostly used in distribution layer and core layer at a hierarchical network design.

What is the difference between Layer 2 and Layer 3 Switches?

Inabilities to handle more BGP functions in inter Autonomous System routing and many other efficient features are some disadvantages when we use a layer 3 switch as a substitute for a router. If we can develop these weak areas routers can become an old story in networking world.

When considering the cost, layer 2 devices are less expensive, but it’s always intelligent to buy  both layer 2 and layer 3 functioning devices (like layer 3 switch), if the company is going to be expanded in future. Further layer 3 switch is capable of handling more traffic and can be described as an efficient and intelligent choice for a medium size or large company where layer 2 devices become handy mostly in small companies.

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