Interpreting important technical parameters of vswitch Devices

Next, I will introduce the important technical parameters of vswitches, so that users can compare different products of different manufacturers when purchasing vswitches. Each parameter affects the performance, functions, and different integration features of the vswitch.

I. Basic parameters

1. forwarding technology: Does a vswitch adopt direct forwarding or storage forwarding technology?
2. latency: How long is the switch's data exchange latency?
3. Management function: How many manageable functions does a vswitch provide?
4. Single/Multi-MAC address type: Is each port a single MAC address or multiple MAC addresses?
5. External monitoring support: Does the vswitch allow external monitoring tools to manage all traffic of ports, circuits, or vswitches?
6. Extended tree: Does a switch provide an extended tree algorithm or other algorithms to detect and limit the Topological Ring?
7. Full Duplex: Does the switch allow simultaneous receiving/sending of ports and full duplex communication?
8. High-speed port integration: Does the switch provide a high-speed port to connect to a key service server or upstream trunk?
The following describes parameters one by one:

(1) forwarding technology: Forwarding Technologies)

The forwarding technology refers to the forwarding mechanism used by the switch to decide how to forward data packets. Each forwarding technology has its own advantages and disadvantages.

Forward through technology: Cut-through)

Once the switch interprets the destination address of the data packet, it starts to send the data packet to the destination port. Generally, when the switch receives the first six bytes of the data packet, it knows the destination address and can decide which port to forward the data packet. The advantage of direct-through Forwarding is that the forwarding rate is fast, the delay is reduced, and the overall throughput is improved. The disadvantage is that the switch has started data forwarding before completely receiving and checking the correctness of the data packets. In this way, in an environment with low communication quality, the switch will forward all the complete data packets and error data packets, which actually brings a lot of junk communication packets to the entire switching network, the switch is misunderstood as a broadcast storm. In short, direct forwarding applies to network environments with good network link quality and fewer error packets.

Storage and forwarding technology: Store-and-Forward)

The storage and forwarding technology requires the switch to decide how to forward after receiving all data packets. In this way, the switch can check the integrity and correctness of data packets before forwarding. The advantage is that there is no incomplete data packet forwarding, which reduces the potential unnecessary data forwarding. Its disadvantage is that the forwarding rate is slower than that of direct forwarding. Therefore, the storage and forwarding technology is more suitable for the network environment with common link quality.

Collision avoidance forwarding technology: Collision-avoidance)

Some vendors 3Com) Switch also provides this vendor-specific forwarding technology. The collision avoidance forwarding technology reduces network error propagation and selects a compromise solution between high forwarding rate and high accuracy rate.

(2) latency: Latency)

Switch latency refers to the interval between the time when the switch receives the data packet and the time when it begins to copy the data packet to the destination port. There are many factors that affect the latency, such as forwarding technology. Vswitches using the forward-through technology have fixed latency. Because a pass-through switch determines the forwarding direction based on the destination address regardless of the overall data packet size. Therefore, the latency is fixed, depending on the rate at which the switch interprets the destination address in the first six bytes of the data packet. Because a vswitch using the storage and forwarding technology must receive complete data packets before it starts to forward data packets, its delay is related to the packet size. If the data package is large, the latency is large; if the data packet is small, the latency is small.
(3) management functions: Management)

The management function of a vswitch refers to how the vswitch controls the user's access to the vswitch and how visible the user is to the vswitch. Generally, vswitch vendors provide management software or remote management switches that meet the requirements of third-party management software. A general switch supports the snmp mib I/MIB II statistical management function. In addition, complicated vswitches support the active monitoring function of RMON by using the built-in RMON group mini-RMON. Some switches also allow external RMON probes to monitor the network conditions of the available ports.

(4) Single/Multi-MAC address type: Single-versus Multi-MAC)

Each port of a single MAC switch has only one MAC hardware address. Each port of a Multi-MAC switch is bound with multiple MAC hardware addresses. A single MAC switch is designed to connect an end user, share resources on the network, or use a non-bridging router. They cannot be used to connect a hub or a network segment containing multiple network devices. Multiple MAC switches have enough storage bodies to remember multiple hardware addresses on each port. Each port of a Multi-MAC switch can be considered as a hub, while a multi-MAC switch can be considered as a hub of a hub. The Buffer capacity of each vendor's switch varies. The Buffer capacity limits the swap address capacity that the switch can provide. Once the address capacity is exceeded, some switches discard other address data packets, and some switches copy data packets to each port for no exchange.

(5) external monitoring support: Extendal Monitoring)

Some switch manufacturers provide "monitoring port" monitoring port), allowing external network analyzers to directly connect to the switch to monitor network conditions. However, the implementation methods vary from vendor to vendor.
(6) extended tree: Spanning Tree)

Because the switch is actually a multi-port transparent bridge device, the switch also has an inherent problem with the bridge device-Topology Loops ). When a data packet in a network segment is transmitted to another network segment through a bridge device, the returned data packet returns the source address through another bridge device. This phenomenon is called "Topological Ring ". Generally, a switch uses the extended Tree Protocol algorithm to let every bridging device in the network know each other and automatically prevents topological loops. A vswitch disconnects a port in the detected "Topological Ring" to eliminate the "Topological Ring" and maintain the integrity of the topology tree in the network. In network design, "Topological Ring" is often recommended for selecting redundant backup links for key data links. Therefore, vswitches with support for the extended Tree Protocol can be used to connect to the swap redundancy of key resources in the network.
(7) Full Duplex: Full Duplex)

The full-duplex port can send and receive data at the same time, but the switch and connected devices must support full-duplex operation. Vswitches with full duplex function have the following advantages:

1. High Throughput): two times the communication Throughput in the ticket mode.
2. Avoid Collision Avoidance): no sending/receiving Collision.
3. Breakthrough length restriction Improved Distance Limitation): Because there is no collision, the length of the CSMA/CD link is not limited. The length limit of the communication link is only related to the physical media.

Full-duplex communication protocols are supported: Fast Ethernet, Gigabit Ethernet, and ATM.
(8) high-speed port Integration: High-Speed Intergration)

A vswitch can provide high-bandwidth "pipe" fixed ports, optional modules, or multi-link tunnels) to meet the switch traffic switching requirements with the upper-level trunk. Prevents trunk communication bottlenecks. Common High-Speed ports include:

FDDI: The application is earlier and has a wide range. However, there is a cost for protocol conversion.
Fast Ethernet/Gigabit Ethernet: easy to connect, low protocol conversion costs, but limited by the network size.

ATM: provides high-speed switching ports, but the protocol conversion costs are high.
Ii. ATM SwitchingATM Switch)

With the development of the ATM switching technology, more and more enterprise networks are using the ATM Switching Technology in the backbone or EDGE networks of high-speed networks. According to the development requirements of existing enterprise computing and to adapt to the technical trend of data network exchange, it is necessary for us to understand ATM. ATM data exchange is composed of a fixed length of ATM cells. Each ATM cell is a 53-byte, 5-byte-long header and a 48-byte-long body ). The header includes virtual path VP, virtual circuit VC, and other address information. The ATM determines the sending source address and receiving destination address of the Cell Based on the VP and VC.

The connections in an ATM switch are divided into permanent virtual circuit PVC and switch virtual circuit SVC. PVC is a permanent hardware circuit connection between the source address and the target address. SVC is a temporary switching circuit connection established according to real-time switching requirements. The biggest difference between the two is that PVC is connected regardless of whether there is data transmission. SVC is automatically disconnected after data transmission is complete. The difference between the two is that in common ATM exchanges, some PVC is used to maintain signal and Management Information Communication and permanent connection, while SVC is mainly used for transmission of a large amount of specific data.

Another feature of ATM switching is that ATM itself is full duplex. Send and receive data simultaneously in different virtual circuits to maintain bidirectional high-speed communication. To meet the communication requirements of Ethernet frame Frames) and ATM Cell Cells, the ATM protocol standard specifies the ATM adapter Layer for data applications ), it works between frame switching and Element Switching, and converts the address information of the Logical Circuit layer of the ethereum into the virtual circuit VC and virtual path VP address information, complete frame-cell conversion and Object-Frame Conversion.

The wide application of ATM Switching brings new challenges to the network monitoring and management of the switching network.
Iii. Virtual LANVLAN)

The development of exchange technology has also accelerated the application speed of the new switch technology VLAN. By dividing an enterprise network into virtual network vlan cidr blocks, network management and network security can be enhanced to control unnecessary data broadcast. In a shared network, a physical network segment is a broadcast domain. In a switched network, a broadcast domain can be a virtual network segment consisting of a group of randomly selected l2 network address MAC addresses. In this way, the division of working groups in the network can break through the geographic location restrictions in the shared network, but is completely divided according to the management function. This workflow-based grouping mode greatly improves the management functions of network planning and restructuring.

The workstations in the same VLAN communicate with each other on an independent hub, regardless of the vswitch they are actually connected. Broadcast in the same VLAN can only be heard by members in the VLAN, instead of transmitted to other VLANs, which can control the generation of unnecessary broadcast storms. In addition, different VLANs cannot communicate with each other without routing, which increases the security of different departments in the enterprise network. Network administrators can configure routes between VLANs to comprehensively manage information exchange between different management units in an enterprise. A vswitch divides VLANs Based on the MAC address of a user's workstation. Therefore, users can freely move their offices in the enterprise network. No matter where they access the exchange network, they can freely communicate with other users in the VLAN.

A VLAN can be composed of devices of a hybrid network type, such as 10 M Ethernet, 100 M Ethernet, Token network, FDDI, and CDDI, it can be workstation, server, hub, and network upstream backbone.

VLAN management requires complex specialized software. It comprehensively manages management objects such as users, MAC addresses, switch port numbers, and VLAN numbers, to enable VLAN division, monitoring, and other functions of the entire network, as well as other extended management functions. Now, the common VLAN division method is based on MAC addresses. However, some manufacturers' switches provide more VLAN Division Methods: MAC addresses, Protocol addresses, switch ports, network application types, and user permissions.

When selecting a vswitch, you should carefully examine the VLAN functions of the selected vswitch, and select a vswitch that meets the requirements and is easy to manage according to your enterprise's actual needs. At the same time, note that most of the VLANs of switches of different manufacturers are incompatible.