What is Switch Aggregation, Its Role and Selection Advice

What is switch aggregation? Switch aggregation refers to the concept of consolidating multiple access layer switches into a single aggregation layer switch in a traditional three-tier network design. The aggregation layer serves as the convergence point for multiple access layer switches and is responsible for handling all the communication traffic from the access layer devices and providing uplink connectivity to the core layer.

What is switch aggregation? Compared to access layer switches, aggregation layer switches require higher performance, fewer interfaces, and higher switching speeds. The primary functions of this layer include:

1. Routing: Determining the optimal path for file transmission within the network.

2. Access control: Including filtering, sorting, and network security measures such as firewalls.

3. Redistribution of routing protocols, including static routing.

4. Inter-VLAN routing and support for other workgroup functionalities.

5. Definition of multicast and broadcast domains. This layer is primarily responsible for implementing network policies.

What is the role of aggregation switches?

Aggregation switches are positioned in the middle of the network architecture, similar to mid-level managers in a company. They are responsible for managing the data from the lower layer (i.e., access layer switches) and reporting it to the upper layer (i.e., core layer switches).

When an aggregation switch receives data from access switches, it performs local routing, filtering, load balancing, and QoS priority management. It also handles security mechanisms, IP address translation, multicast management, and other processes. Finally, based on the processing results, the data is forwarded to the core layer switches or undergoes local routing to ensure the smooth operation of the core layer.

Thus, aggregation switches possess various functionalities such as source and destination address filtering, real-time policies, security measures, network isolation, and segmentation. Compared to access switches, aggregation switches offer better performance and higher switching speeds.

However, in some network architectures, there may be only access and core switches without aggregation switches. This is typically the case for small and simple networks with short transmission distances. In order to reduce network costs and maintenance burdens, aggregation switches are not deployed. However, if the number of network users exceeds 200 and is expected to continue growing, it is recommended to deploy aggregation switches.

Considerations for choosing aggregation switches:

1. Backplane bandwidth and packet forwarding rate: Backplane bandwidth and packet forwarding rate are important factors to consider when evaluating a switch's ability to handle data packets. Higher backplane bandwidth and packet forwarding rate indicate stronger data processing capabilities. It is crucial to choose a suitable aggregation switch based on the actual requirements to avoid performance bottlenecks or wasteful resource allocation.

2. Port types and numbers: Since aggregation switches need to aggregate data from multiple access switches and forward it to the core switch, the port types and numbers of both upstream and downstream switches should be considered. For example, if the aggregation switch needs to connect to access switches with SFP fiber ports, it is advisable to choose an aggregation switch with downstream ports that support SFP fiber ports. The specific number of ports depends on the number of access switches to be connected, such as 24-port or 48-port aggregation switches.

3. Port speeds: The selection of port speeds for aggregation switches should consider both upstream and downstream links. The port speeds can be consistent or different. For example, both upstream and downstream links can be Gigabit Ethernet, or the port speed for the upstream link can be Gigabit Ethernet while the downstream link is 10 Gigabit Ethernet. The final determination depends on the upstream port speed of the access switches and the downstream port speed of the core switch.

4. Functional management: Unlike core switches, aggregation switches can be either Layer 2 or Layer 3 switches. When a Layer 2 switch is used as the aggregation switch, routing and management policies are determined by the core switch rather than the aggregation switch.

This article wraps up "what is switch aggregation" and suggestions for choosing an aggregation switch. By considering these factors, network administrators can make informed decisions when selecting aggregation switches that align with their network architecture, performance needs, and future growth plans.