Switches are an important component in every network infrastructure. They receive data packets and forward them to the desired destination in an intelligent process. Selecting a suitable switch depends on network requirements. This article shows what criteria companies need to consider when purchasing a switch for their computer centre.

Switches are a key element in ensuring that networks work reliably. They manage a MAC (Media Access Control) table for assigning addresses to ports via which they forward the data packets from the correct ports as quickly as possible to the desired destinations. Switches are normally operated on the data link layer (Layer 2) or the network layer (Layer 3) of the OSI model and support important standard protocols such as the Spanning Tree Protocol (STP) or the Multiple Spanning Tree Protocol (MSTP). Switches are managed and controlled either by means of command lines, a web interface or special control software.

Requirements determine the choice

Manufacturers such as Cisco, Juniper, etc. offer a large number of switch models at different prices. The question is: which is the right one for your company’s IT structure? The basic principle that applies here is that the requirements for specific applications in the network are decisive when it comes to choosing a suitable switch.

The following questions can assist in making the right choice:

  • Deployment location: Where is the switch going to be deployed or what equipment is going to be connected?
  • Physical ports: How many and what type of physical ports are necessary (RJ45, SF/SF+)?
  • How many users are there? How much traffic do they generate?
  • What bandwidth is required (1 GBit/s, 10 GBit/s, 100 GBit/s)?
  • What functionalities do the users need? (Layer 2 or Layer 3, VoIP etc.)
  • What protocols and security functions are to be supported (VLAN, NAC, QoS, Spanning Tree)?
  • What type of management is most practical (web interface, CLI, SNMP, central management)?
  • Power over Ethernet: Do firms need PoE/PoE+ for their clients, server, telephones, etc.?
  • How high is the current level of virtualisation in the computer centre and what will it be in future?
  • Latency: What switching method does the company prefer? (Conventional “Store-and-Forward” methods, where additional latencies occur due to the data packets being checked or faster methods such as Fast Forwarding or Cut Through Switching?)
  • Stacking: Is stacking required? With stacking, a number of physical switches are grouped to form a logical device. This simplifies management as multiple devices can be managed using one user interface. It also enables highly available network topologies.
  • Converging networks: Firms that want to unify their separate LAN/SAN networks need switch models that support LAN and SAN convergence.
  • East-West traffic: Nowadays, an increasing amount of data in the computer centre flows between virtual and physical servers, which is why firms need switches with sufficient backplane throughput capacity to prevent bottlenecks.
  • Energy consumption: To what extent do Green IT functions play a role? (Fanless design, energy-efficient power supplies, etc.)

Four types of switch

The more demanding the requirements the more likely the decision in favour of a data centre switch. In addition there are three further categories that fit the classical three-tier network model: core switches, distribution switches, access switches.

  1. Core switch: Core switches transport packets with a high throughput rate and high performance level. They are used in the backbones of high-speed networks, IP networks and in computer centres. Core switches include no redundancy checks or error correction.
  2. Distribution switch: These switches do most of the work in the distribution layer in the company network. They connect the core and access tiers with one another. Furthermore, they enforce network policies, filter data traffic by means of access lists and manage Quality of Service policies to prioritise packets.
  3. Access switch: As they interact directly with the end-user’s devices, access switches have a large number of ports. Of all the various types of switch, they usually have the lowest throughput rate per port but they provide many functions that are especially tailored to endpoints. For example, they support Power over Ethernet (PoE) for the power supply to the connected endpoints and provide security functions such as port security or 802.1X authentication.
  4. Data centre switch: These devices are mostly used in companies and at Cloud providers with a high level of virtualisation (including SDN). They provide the corresponding port capacity and port throughput to handle internal data traffic in the computer centre (East-West traffic) as well as external traffic. They link LAN and SAN and, thanks to various functions, increase the availability of business-critical applications. They also support a fabric architecture in the network with two tiers (leaf-spine topology) in which, in contrast to conventional 3-tier networks, every access switch (leaf) connects to every aggregation switch (spine). The result is larger bandwidths and shorter latencies.

Switches from Juniper and Cisco

Manufacturers such as Juniper or Cisco provide switches from all categories.

The EX Series Ethernet Switches from Juniper, for example, are available in three categories as 1 GbE Multigigabit access switches that provide network access for companies with PoE and MACsec (Media Access Control Security) encryption. They are also available as 10 GbE aggregation switches with fixed configuration for provision in enterprise campus environments. The EX9200 (also with SDN-capability) and EX9250 devices feature flexible core switching for business-critical provision in high-density enterprise campus environments.

The switches in the QFX Series safeguard and automate networks in computer centres. They form the basis for establishing flexible high-performance fabrics, improve the reliability and agility of the network and thus simplify the path to the Multicloud. Juniper divides the eight switches in the QFX Series into three categories: “Access and Leaf“, “Lean Spine” and “Core and Spine”.

Cisco too offers an extensive portfolio of switches. These include the Catalyst 9500, Catalyst 9400, Catalyst 9300, Catalyst 9200, Catalyst 3850, Catalyst 3650 data centre switches and the 9000 Series Cisco Nexus Switches with specific circuits for SDN. This increases the bandwidth, the number of ports, the size of the routing tables and that of the buffer. They also enable leaf-spine architecture.