Generally, a Layer 2 switch is one of the essential equipment used to connect all network and client devices. But for now, layer 3 switch is thriving in data centers, complicated enterprise networks, and commercial applications with the growing diversity of network applications and converged network implementations. The question arises: layer 2 vs. layer 3 switch; which is the network switch of choice?
Layer 2 Switch and Layer 3 Switch: What Are They?
Layers 2 and 3 switches are adopted in the Open System Interconnect (OSI) model, a reference model for describing and explaining network communications. The OSI model has seven layers: Application layer, Presentation layer, Session layer, Transport layer, Network layer, Data Link layer, and Physical layer, among which layer 2 and layer 3 refer to the data link layer and network layer, respectively, and the switches working in these layers are called layer 2 switches and layer 3 switches.
Layer 2 vs. Layer 3 Switch
Layer 2 and Layer 3 differ mainly in the routing function. A Layer 2 switch works with MAC addresses only and does not care about IP addresses or any items of higher layers. A layer 3 switch, or multilayer switch, can do all the jobs of a layer 2 switch and additional static and dynamic routing. That means a Layer 3 switch has both MAC address table and IP routing table and handles intra-VLAN communication and packet routing between different VLANs. There is also layer 2+ (layer 3 Lite) switch that adds only static routing. Other than routing packets, layer 3 switches also include functions that require understanding the IP address information of data entering the switch, such as tagging VLAN traffic based on IP address instead of manually configuring a port. Layer 3 switches are increased in power and security as demanded.
When lingering between Layer 2 and Layer 3 switches, you should consider where they will be used. If you have a pure Layer 2 domain, you can simply go for a Layer 2 switch. A pure Layer 2 domain is where the hosts are connected, so a Layer 2 switch will work fine there. This is usually called the Access layer in a network topology. If you need the switch to aggregate multiple access switches and do inter-VLAN routing, then a Layer 3 switch is required. This is known as the distribution layer in the network topology.
| Item | Layer 2 Switch | Layer 3 Switch |
|---|---|---|
| Routing Function | Mac address only | Supports higher routing such as static routing and dynamic routing |
| VLAN Tagging Based on IP Address | No | Yes |
| Inter-VLAN | No | Yes |
| Using Scenario | Pure Layer 2 domain | Aggregate multiple access switches |
Layer 2 vs. Layer 3 Switch: Key Parameters to Consider When Purchasing
If you are buying a Layer 2 or Layer 3 switch, there are some key parameters that you should check out, including the forwarding rate, backplane bandwidth, number of VLANs, the memory of MAC address, latency, etc.
The forwarding rate (or throughput rate) is the forwarding capabilities of a backplane (or switch fabric). When the forwarding capabilities are greater than the sum of speeds of all ports, we call the backplane non-blocking. The forwarding rate is expressed in packets per second (PPS). The following formula gives how to calculate the forwarding rate of a switch:
Forwarding Rate (pps) = number of 10Gbit/s ports * 14,880,950 pps + number of 1 Gbit/s ports * 1,488,095 pps + number of 100Mbit/s ports * 148,809 pps
For example, FS S5850-32S2Q has 32 10 Gbit/s ports and 2 40 Gbit/s ports, so its forwarding rate is:
32 * 14,880,950 pps + 2 * 4 * 14,880,950 pps = 595,238,000 pps ≈ 596 Mpps
The following parameter is the backplane bandwidth or switches fabric capacity, which is the sum of the speeds of all ports. The sum of speeds of all ports is counted twice, one for Tx direction and one for Rx direction. Backplane bandwidth is expressed in bits per second (bps or bit/s).
Backplane Bandwidth (bps) = port number * port data rate * 2
So the backplane bandwidth for S5850-32S2Q is:
(32 * 10 Gbps + 2 * 40 Gbps) * 2 = 800 Gbps
Other critical parameters are the number of VLANs that can be configured. Generally, 1K = 1024 VLANs is enough for a Layer 2 switch, and the typical number of VLANs for a Layer 3 switch is 4k = 4096. The memory of the MAC address table is the number of MAC addresses that a switch can keep, usually expressed as 8k or 128k. Latency is the delay time that a data transfer suffers. It must be as short as possible, so the latency is usually expressed in nanoseconds (ns).
What is the difference between an Ethernet splitter, an Ethernet switch, and an Ethernet hub?
An Ethernet splitter is a small gadget that allows you to make one cable act as two cables. It helps you save on the length of cable to use from the modem to the devices. However, it does not mean you can connect more devices to it. For example, you connect your modem to your device using two LAN ports, add a splitter, connect a single cable then add a splitter on the other end to connect to the devices you want to connect. The downside of this is the limited speed (100mpbs per connection) and you do not save on your Ethernet port.
An Ethernet switch allows you to add ports without affecting the speed of the network. One device can communicate directly to the other without having to go through a high-traffic network.
An Ethernet hub, on the other hand, is a thing of the past. Because the message has to go through a high-traffic network, the result is distorted and communication is slow. The number of devices working at the same time predicts the performance of the network. The more devices working, the slower the network is.
What does 10/100/1000 mean on a switch?
The 10/100/1000 mark on your Ethernet switch means it is a high-end switch because it can detect device speed from 10Mbps, 100Mbps, or 1Gbps.
What is the difference between managed and unmanaged switches?
An unmanaged switch is easier to use even for an untrained person since it’s just plug-and-play. A managed switch, on the other hand, allows you to control priority channels for better performance. In terms of security, managed switches have deeper security layers so only an authorized technician has access privileges so it’s not easily tampered with.
However, for home use and small businesses where a retainer technician can help, unmanaged switches are the best option. For large businesses that need an extra layer of security to protect their data and other related concerns, a managed switch gives you the peace of mind.
Summary
This post has explained the differences between Layer 2 vs. Layer 3 Switch. A comparison of their functions is also made in the hope of solving the problem of deciding between these devices. Also, critical parameters for measuring a Layer 2 or Layer 3 switch are discussed. It is not always the case that a more advanced device is better, but choosing the most appropriate one for your specific application and budget is important to keep in mind.