What is the difference between stack and cascade of vswitches?

Level Expansion

The cascade expansion mode is the most common and direct extension mode. Some earlier networks are built using hubs as the cascade devices. Because the hub was already very expensive at that time, most enterprises could not choose a switch as a level-1 device. This is because most working group users require access, which is generally connected from a port on the hub to the dashboard. In this way, the access capability has been greatly improved. However, due to some interference and human factors, the overall performance is very low and only needs to be met by multiple ports, there is no time to consider the forwarding and switching function. Considering the forwarding performance and port attributes of different vswitches, the current cascading expansion mode can easily achieve multi-user access through a certain Topology Design. The typical structure of the cascade mode is shown in Figure 1.

The hierarchical connection mode is the most ideal way to build a large lan. It can combine various Topology Design Technologies and redundancy technologies to achieve a hierarchical network structure. For example, redundant Topology Design through dual-homing, the link aggregation technology is used to achieve redundancy and up link bandwidth expansion. These technologies are now very mature and widely used in various LAN and man networks.

The cascade mode uses common Ethernet ports for hierarchical interconnection, such as the 100 m FE Port, GE port, and emerging 10GE port.

The cascade mode is a mainstream technology in Ethernet extended port applications. It uses a unified network management platform to manage devices across the network, such as topology management and fault management. The hierarchical connection mode is also facing challenges. When there are many layers and a large convergence ratio exists between layers, Edge Nodes experience a lot of switching and caching, there will be a certain latency. The solution is to converge upstream ports to reduce the convergence ratio, improve the performance of the Upper-end devices, or reduce the level of connection. In the level-4 connection mode, we recommend that you do not have more than four layers to Ensure network efficiency. If the edge node of the network has a port that is extended by a radio Ethernet device such as a hub, because it is in a pass-through mode, there is no switch and it is not included in the hierarchy. However, note that, in the CSMA/CD mechanism that the hub works on, the impact on network performance caused by conflicting delivery may be much greater than that caused by SWITCH-level connections.

The hierarchical connection mode is an inevitable choice for building a structured network. The hierarchical connection uses a common cable (optical fiber), and each component can be placed in any position, which is very conducive to integrated wiring.

Stack technology expansion

Stack technology is another type of technology that currently uses a large number of port extensions on Ethernet switches. It is a non-standard technology. Different vendors do not support hybrid stack. The stack mode is determined by each vendor and does not support the topology structure. Currently, there are two popular stacking modes: Chrysanthemum chain mode and star mode. The biggest advantage of stack technology is that it provides simplified local management and manages a group of switches as an object.

Chrysanthemum chain Stack

Chrysanthemum chain stack is a stack Technology Based on the cascade structure. It 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. However, in terms of exchange efficiency, the same-level connection mode is at the same level. The Chrysanthemum chain stack usually uses one high-speed port and two high-speed ports. The structure of the two is shown in figure 2. In the mode of one high-speed port (GE), the uplink and downlink of the same port are respectively sent and received, forming a ring structure, data exchange between any two member switches takes one week. The exchange ports of all switches are inefficient, especially when many layers are stacked, stacked ports may become serious system bottlenecks. Two high-speed ports are used to implement chrysanthemum chain stacking. Because more high-speed ports are occupied, you can choose to implement ring redundancy. Compared with the cascade mode, the chrysanthemum chain stack mode does not have topology management and generally cannot be distributed. It is applicable to single-node organizations that require high-density ports and can be used on the edge of the network.

Due to the need to eliminate the broadcast storm caused by the loop, the chrysanthemum chain structure is normally at any time, A route entry from a vswitch to the master vswitch can only use one high-speed port (that is, one high-speed port cannot share the uplink data pressure of the vswitch ), all upstream switches are required for switching (see figure 3 ).

Chrysanthemum chain stack is a type of simplified stacking technology. It is mainly an extended port technology that provides centralized management, the forwarding efficiency between multiple vswitches is not improved (the efficiency in Single Port mode is much lower than that in cascade mode). More high-speed ports need to be provided by hardware, and the software achieves up link redundancy. Generally, the number of layers in the chrysanthemum chain stack should not exceed four layers. all Group members must be placed close enough (generally on the same rack ).

Star stack is an advanced stack technology. For vswitches, an independent or integrated high-speed switching center (stack Center) is required ), all stacked hosts are uplinked to the unified stack center through dedicated (or general high-speed ports) ports. The stack center is generally a hardware switching unit based on dedicated ASIC, based on its switching capacity, the bandwidth is generally between 10-32 GB, and its ASIC switching capacity limits the number of layers in the stack (see figure 4 ).

ArticleInput: CSH responsible editor: CSH