What is Layer 2 Switch?
Layer 2 switches, also known as Ethernet switches or LAN switches, are network devices that operate at the Data Link Layer (Layer 2) of the OSI (Open Systems Interconnection) model. These switches are designed to connect multiple devices within a local area network (LAN) and facilitate the efficient forwarding of Ethernet frames based on their Media Access Control (MAC) addresses.
What you need to know about layer 2 Switch
- Layer 2 switches build and maintain a MAC address table, also known as a forwarding table or Content Addressable Memory (CAM) table, which maps MAC addresses to the physical ports on the switch.
- They use the MAC address table to make forwarding decisions. When a frame is received, the switch looks up the destination MAC address in its table and forwards the frame out of the appropriate port(s) to reach the intended recipient device(s).
- They forward broadcast frames within the same VLAN (Virtual Local Area Network) to all ports except the incoming port. However, they do not propagate broadcasts between VLANs. Multicast traffic is handled similarly, with limited support within the same VLAN.
- Support VLANs, which enable logical segmentation of a physical network into multiple broadcast domains. VLANs help improve network performance, security, and manageability by isolating traffic and controlling broadcast domains.
- Layer 2 switches can implement basic traffic filtering based on MAC addresses. This enable network administrators to control the flow of traffic within the LAN.
What is layer 3 switch?
A Layer 3 switch, also known as a multilayer switch or a routing switch, is a network device that operates at both the Data Link Layer (Layer 2) and the Network Layer (Layer 3) of the OSI (Open Systems Interconnection) model. Layer 3 switches combine the functionality of traditional Layer 2 switches with that of routers, allowing them to perform routing functions in addition to switching functions.
What you need to know about layer 3 Switch
- Like Layer 2 switches, Layer 3 switches maintain a MAC address table to forward Ethernet frames within the same LAN segment based on MAC addresses.
- They can route traffic between different IP subnets or VLANs by making forwarding decisions based on the destination IP addresses in the packet headers.
- They can route traffic between different VLANs. This enable communication between devices in separate VLANs within the same network infrastructure.
- Support dynamic routing protocols such as OSPF (Open Shortest Path First), RIP (Routing Information Protocol), or EIGRP (Enhanced Interior Gateway Routing Protocol) to dynamically exchange routing information and make routing decisions.
- Usually support QoS features. This allows network administrators to prioritize certain types of traffic based on criteria such as packet classification, DSCP (Differentiated Services Code Point) markings, or IP precedence.
- They can also be configured with static routes to manually specify how traffic should be forwarded to specific destinations.
- Can implement ACLs to control the flow of traffic based on various criteria such as source/destination IP addresses, TCP/UDP port numbers, or protocol types.
- Can support multicast routing protocols such as PIM (Protocol Independent Multicast) to efficiently distribute multicast traffic within a network.
Layer 2 vs. layer 3 switches: Key Differences
| Basis | Layer 2 Switch | Layer 3 Switch |
| Functionality | Operates at the Data Link Layer (Layer 2) of the OSI model. | Operates at the Network Layer (Layer 3) of the OSI model. |
| Addressing | Works with MAC addresses for forwarding decisions. | Works with IP addresses for forwarding decisions. |
| Packet Forwarding | Forwards packets based on MAC addresses only. | Forwards packets based on both MAC and IP addresses. |
| Routing | Does not perform routing. | Can perform basic routing functions, such as IP routing. |
| VLAN Support | Supports VLANs (Virtual Local Area Networks). | Supports VLANs as well as inter-VLAN routing. |
| Traffic Management | Provides basic traffic filtering based on MAC addresses. | Can implement more sophisticated traffic management features, such as access control lists (ACLs) and Quality of Service (QoS). |
| Broadcasts | Propagates broadcast frames within the same VLAN. | Does not propagate broadcasts between VLANs. |
| Multicast Support | Generally limited multicast support within VLANs. | Can support inter-VLAN multicast routing. |
| Network Complexity | Suitable for simpler network environments with less need for routing functionality. | Suitable for more complex networks requiring routing between subnets and VLANs. |
| Cost | Typically lower cost compared to Layer 3 switches. | Generally higher cost due to additional routing capabilities. |
| Example | Cisco Catalyst 2960 Series | Cisco Catalyst 3650 Series |