What is an Ethernet Network Switch?

What is an ethernet network switch? Most people network engineers would say a switch is the most trivial device needed for connecting computers. But in order to understand better it´s crucial to understand what is an ethernet switch in networking.

A switch (also known as a switching hub) is a high-speed device that uses packet switching in order to receive, process, and forward data mainly to multiple devices on a local area network. A LAN switch operates at the data link layer (Layer 2) or the network layer of the OSI Model, and as such, it can support all types of packet protocols such as Spanning Tree Protocol (STP), Multiple Spanning Tree Protocol (MSTP), Rapid Spanning Tree Protocol (RSTP), Link aggregation and Multiple MAC Registration Protocol.

Your network would not be a network without a network switch. This sounds indeed very logical. Now consider how to decide for and which network switch. What do you take into account for your decision? What is important for you? You need a reliable switch. Welcome to Black Box switches. Switches come with various rack designs, port options and features. Do you want to go for Gigabit technology or at least have the chance for upgrading to Gigabit? Do you want to have at least some control who is doing what, when and from where? Talking about the features there are many protocols and abbreviations out there.

Black Box is not hiding technology behind any IEEE Numbers. Here you have a short list of the main and important features:

• SNMP: (Simple Network Management Protocol) enables administrators to have full control anytime upon the network, its traffic and users. To fully use SNMP functions administrators need a SNMP software like HP Openview or NINO (http://nino.sf.net) SNMP functions are to display port status, fan status, temperature and many more issues of and around the switch and its functionality. Alerts (Traps) can be sent out to the SNMP software to automatically take actions needed or to display on a screen or to send out SMS alerts.
• Port Mirroring: The switch has the functionality to output all incoming traffic to one special port. This function allows system administrators to run Sniffer Software like Ethereal (http://www.ethereal.com)
• ACL: (Access Control Lists) The switch allows the administrator to open or close certain or the complete network traffic for users. Through this functionality unwanted network traffic like usage of P2P software can be blocked making the usage of unwanted software like P2P software impossible. More than that only certain computers identified by their MAC address can get access to the network.
• Bandwidth Control: The switch can be configured so that certain ports can only use a certain amount of bandwidth. This function is very useful when uplink bandwidth is limited and administrators want to reserve bandwidth for special users, services or computers.
• VLAN: (Virtual Local Area Network) The switch can be seperated into more and smaller switches with the Port Based VLAN feature. This can be used to seperate the network traffic of departments. With Tag Based VLAN (802.1q) the switch is able to communicate with other Tag Based VLAN capable switches to which Group a port belongs. This allows the Basic Port Based VLAN functionality to be expanded over a whole network.
• Spanning Tree: (STP/802.1d) The switch can detect network loops and is able to break the loop by disabling one of the uplinks. This allows administrators to build up network rings to build up redundancy concepts.
• Rapid / Fast Spanning Tree (RSTP/802.1w): While Spanning Tree (see above) is not very fast (the switch over time can be up to five minutes) the newer Fast and Rapid Spanning Tree protocols can switch over within milliseconds to keep the redundant network running when one loop fails.
• Port Trunking: (Link Aggregation/802.3ad) The switch is able to combine ports into a trunked port. This allows administrators to build up high bandwidth uplink ports between switches. Port Trunking is not like load balancing. This feature is only useful when many source and target computers are connected to the switch.
• 802.1X This authentication protocol is a security feature. The network accessing computers need to have 802.1X capability to log into the network. The switch keeps a database of known clients.
• Quality of Service (QoS): The switch is able to prioritize network traffic. This feature is used for VoIP applications where it is necessary that IP traffic for Voice over IP is being transmitted and received "just-in-time"
• Layer 3 (L3): Layer III enables system administrators to run different subnets on the network. While this is a feature for security it is also a performance feature.
• PSE (Power Sourcing Equipment): This device is providing Power over Ethernet according to 802.3af. So administrators can power Wireless and VoIP devices without additional power supplies.
• PD (Powered Device): This device can be powered by 802.3af.

For more information on managed verses unmanaged switches, check out our Black Box Explains page on The difference between managed, unmanaged, and web-smart switches.