Analysis of advantages and challenges of Stackable Switches

Bkjia.com comprehensive report: a stack switch connects several switches through a dedicated stack module to increase the port density of the network access layer exponentially. Some Manufacturers' switches can be managed as a network element after being stacked, which simplifies the network structure.

Advantages of Stackable Switches

Stackable switches have the advantages of rapid deployment, good value, scalability, and ease of management. They are widely used, especially in e-commerce applications.

However, evaluating a stackable switch based entirely on the price of each user port does not reflect all situations. In fact, if the vendor calculates the price per port based on the configuration that does not meet the actual conditions or makes other assertions, it may mislead users to judge a product based on the price.

Challenges facing stack Technology

Today's traffic models are becoming more diversified, such as instant communication between voice and images, which leads to a dramatic increase in client-to-client access and traffic between edge switches. These are all the problems that previous stackable switches do not face.

The first problem is stack bandwidth. We know that the forwarding capability of a vswitch usually enables line rate switching between ports. But what is the stack bandwidth between vswitches? Let's look at the vswitches on the market today. The stack bandwidth is usually 1 Gbps. The BayStack470 of the Nortel Network provides Gbps stack bandwidth. But when the traffic across vswitches is large, do we need a larger stack bandwidth?

Second, stack introduces the reliability of devices. Will the failure of one switch or one stacked cable affect the work of other switches? Will the network management fail? How long can I recover to normal? Most vswitches on the market, despite having dedicated stack modules, still follow the principle of gigabit interface interconnection. When multiple switches are connected into a ring by stacked cables, it looks like a network device, but it is like wearing them together with a gigabit interface. Due to SpanningTree, one of these stacked cables is blocked by the protocol, seriously affecting forwarding performance. When a switch or a stacked cable fails, the SpanningTree converges again, and the network will be unavailable for at least dozens of seconds, which is unacceptable to users today. In this case, key applications such as voice, video, and electronic trading will be seriously affected.

In 1995, when the BayStack450 switch came out, the Nortel Network solved these problems. BayStack450 provides a "secure stack" of 2.5 Gbps), which can be self-healing within one second in the event of a fault. This secure stack not only provides protection when a device fails, but also provides uninterrupted service protection when the user upgrades the network. As user services grow, the network scale will expand. When the access switch needs to be resized, we need to open the stack and add it to the new switch. The secure stack does not affect the switch in operation. This stack technology also enables the entire stack to use an IP address for network management, just like a network device.

The integration of voice, image, data, and storage services enables more and more businesses to be based on the network. People can do more things on their desktops, and the network edge is under increasing pressure. In addition to stack technology, edge switches are challenged in terms of performance, reliability, security, QoS, and manageability.

Features of Stackable Switches

Stack bandwidth

Currently, the biggest challenge for a stack switch is how to solve the problem of insufficient bandwidth from the hardware. Currently, most switches on the market are stacked through Gigabit expansion slots, with a stack bandwidth of only 2 Gbps, which can easily cause data flow congestion. Therefore, we recommend that you use products with high stack bandwidth. Currently, stack bandwidth can reach dozens of Gbps.

Currently, the number of stacked switches on the market can reach 6 to 9, or even higher. This high stack function can achieve flexible network expansion. However, you must note that the performance of the vswitch is not affected while implementing high stack.

Stack Mode

Stack switches generally have two stack modes: Star stack and Chrysanthemum chain stack. Chrysanthemum chain stack is a cascade-based stack technology that has no special requirements on the switch hardware. It supports port concatenation and software at a relatively high speed, finally, we can build a multi-switch cascade structure. Through the loop, we can achieve redundancy to a certain extent. The Chrysanthemum chained stack mode does not have topology management. It is applicable to a single node mechanism that requires high-density ports and can be used for network edges. The star stack mode is applicable to a single-node LAN that requires high-efficiency and high-density ports. The star stack mode overcomes the high latency impact of multi-layer forwarding in the chrysanthemum chain stack mode, but needs to provide a high-bandwidth matrix, the cost is high, and the matrix interface is generally not universal. The stacked ports of both the stack center and the member switch cannot be used to connect to other network devices.

Innovative FAST technology

The innovative FAST technology of the Nortel Network Enables two-way data transmission between switches in the stack at the same time. The bandwidth of the stack is as high as 640 Gbps. Each switch has a full duplex bandwidth of 40 Gbps between the upstream and downstream units. The FAST technology also provides an optimized data transfer-shortest path algorithm in the stack. For example, a stack has eight switches. When the third switch sends a packet to the second switch, the packet will not be sent to the fourth and then to the fifth ...... In this case, the first vswitch is used for pushing to the second vswitch. FAST technology uses the shortest path algorithm to make the data transmission between switches always use the shortest path for direct transmission on the full-duplex 40 Gbps connection between the second and third switches ). This not only improves the usage efficiency of stack bandwidth, but also reduces the latency of data transmission.

FAST technology also inherits the advantages of "secure stack. It enables smooth network upgrade without affecting user services in case of a fault. When adding a new switch to the stack, you only need to perform a simple connection. FAST technology makes it a "plug-and-play" process.

Multiple ports

Currently, many vswitches provide Ethernet ports at 10/100 Mbps. However, in the face of rapid technological development, it is recommended that you consider providing a Mbps port and a GBIC port switch to ensure future Gigabit access and optical fiber access needs. Pay attention to whether the stack link can achieve full duplex, stacking unit and uplink redundancy, and whether there is a single fault point. The star stack structure usually has a single fault point.

Availability

The stackable switch stack is used as an independent unit, which requires high availability of the device. The operation of the entire group of devices cannot be affected because of a problem with the stack unit. Therefore, selecting a stackable switch requires high availability and intelligent features such as plug-and-play.

Manageability

Many studies have demonstrated that the cost for running and managing a product during its lifecycle is higher than the initial purchase cost. Therefore, manageability is another key factor in evaluating the overall value. The inherent advantage of Stackable switches is that it is easier to manage a single logical entity than to manage multiple devices that must be configured and monitored independently. However, there are still some other factors that need to be studied, including the service quality QoS for priority data streams), the ability to execute policies, the ability to manage VLAN transmission streams, and ease of management and operation.

To simplify management, stack switches must be able to provide various Web-based management methods, as well as cross-Switch configuration and software upgrade.