EOR and TOR Switching from the Perspective of EOR and TOR Architecture

NADDOD Neo Switch Specialist Jan 13, 2023

The traditional three-layer network structure is divided into the access layer, aggregation/distribution layer and core layer, and the cabling architecture based on the three-layer network structure includes EOR, MOR and TOR, of which the MOR architecture only has a slight difference in the deployment location of EOR, and they have the same advantages and disadvantages. So what is the difference between the remaining EOR and TOR architectures? What are the differences between switches used in the two architectures?

EOR Architecture and EOR Switches

What is EOR Architecture?
EOR architecture is equipped with network cabinets at the side ends of each row of cabinets (maybe one, or one at the beginning and one at the end) to provide a unified network access point. The server NICs on the server cabinets are connected to the patch panel of the same cabinet through short distance network patch cables, DACs, and fiber optic patch cables, and the cables on the patch panel are bundled through cable ties and connected to the network cabinets at the far end of each row through the trunking or floor.

What is an EOR Switch?
A switch installed in an EOR architecture is called an EOR switch and is placed centrally in a network cabinet. the EOR architecture is managed on a per-row basis rather than per cabinet, which places higher demands on the EOR switch. If an EOR switch fails, it will affect a row of servers. In general, chassis switches are more suitable for use in an EOR architecture than fixed switches. Chassis switches have significant advantages in the following aspects:

  • Greater flexibility, as chassis switches can be configured with different rates and different numbers of interface boards, providing flexible options for access to servers in different data centers.
  • Higher reliability, with frame switches featuring multiple power modules, multiple fan modules, and multiple switch boards, providing higher reliability in the face of access volumes for entire rows of cabinets.
  • Stronger scalability, the frame switch can replace rate interfaces, when the data center access rate is upgraded, only the rate board is replaced, reducing equipment replacement costs.

TOR Architecture and TOR Switches

What is TOR Architecture?
TOR architecture is an extension of EOR architecture, which deploys 1-2 access switches on each server cabinet. The servers are connected to the switches in the cabinet through cables, and the uplink ports of the switches are connected to the aggregation switches in the network cabinet through cables.

What is a TOR Switch?
A switch installed in a TOR architecture is called a TOR switch. Although literally a TOR switch is a switch installed on top of a cabinet, in reality a TOR switch can be installed on top of the cabinet, in the middle or at the bottom, because it is most convenient to install on top, so it is more common to install on top. Since the smaller the size the better, TOR switches are usually 1U-2U fixed switches because they are installed inside the server cabinet.

Selection of TOR Switches in TOR Architecture

Although the TOR architecture is more suitable for new data centers, in order to avoid the problems of low switch port utilization and difficult configuration management and maintenance, parameters such as the number of ports, uplink rate and features of the switch should also be considered when selecting a TOR switch.

● The number and rate of TOR switch ports are closely related to the server port rate. When the server port rate is GE port, you can choose a switch with 24 or more downlink GE ports and 10G or higher uplink rate.
Note: For the port utilization problem, if the switch ports of one server cabinet are not fully utilized, try cross wiring with adjacent server cabinets, which can reduce port waste to a certain extent.

● To reduce the difficulty of configuration management for high-volume TOR switches, it is best to choose a switch with ZTP function. The switch can obtain the version file from a USB flash drive or file server and load it automatically to achieve field-free configuration of the device, which can enhance the efficiency of deployment.


Is TOR architecture always applicable to modern data centers? In fact, it is not. In recent years, the network structure of data center has changed a lot, and the Layer 2 network structure represented by the spine leaf network topology is becoming the new favorite of data center at a rapid pace. The good thing is that TOR switches can still act as leaf switches in the spine leaf architecture and connect to the backbone switches to achieve a perfect transition from Layer 3 to Layer 2 network structure.