Viewpoint: measure the test taker's knowledge about the parameters and performance characteristics of the backbone switch.

I believe that many users are not very familiar with the parameters and performance of the backbone switch. According to the current situation in the exchange market, the demand for the backbone switch is not very good. Users also choose to purchase the switch based on their own needs, and product performance. Ethernet Switching is a very active part of network development, especially with the continuous development of ASIC Technology, the product performance and price ratio have been greatly improved, so that the Ethernet switch technology has a broader development space. A backbone Switch is based on a powerful ASIC chip. It retains the basic features of a common LAN Switch and uses an Ethernet forwarding chip as the basis for forwarding.

1. Important Technical Parameters

1. Support for more VLANs

In a backbone switch, Ethernet technology can be used to easily implement VLANs. The number of VLANs supported is also larger than that supported by common Ethernet switches. Generally, 4 K VLANs are supported. Some backbone switches can even support port VLANs, so that the number of VLANs is no longer limited to the limit of up to 4 K VLANs in the 802.1q protocol, supports n × 4 K (n indicates the number of ports) VLANs. In some backbone switches, dual (multiple) VLAN tags are also supported, which makes VLAN-based forwarding hierarchical and breaks through the limit of 4 k vlan numbers.

2. Larger MAC Address Table

Ethernet Forwarding is mainly based on the MAC address table. Among the backbone Switch parameters, the port density is relatively high, and multiple common LAN switches can be mounted to the backend Switch, for example, all users in the entire enterprise network or users in the whole community. Therefore, the number of MAC address tables is usually above 10 KB, generally between 32 KB and 32 KB ~ 256 k. Therefore, when selecting a backbone switch, the number of MAC address forwarding tables is an important indicator.

3. Support for layer-3 Switching

As a backbone switch, it must also have a layer-3 Switch capability, which is a notable feature of the backbone switch. Common LAN Switch switches support layer-2 MAC address forwarding, and some support layer-3 forwarding to implement limited layer-3 routing. However, as a backbone switch, it is necessary to support cross-VLAN forwarding. This is inseparable from the network location where the backbone switch is located in the enterprise network, campus network, and Metro interface. Therefore, a layer-3 switch must have a layer-3 interface. Generally, layer-3 interfaces are divided by VLAN as the basic unit of layer-3 logical interfaces. Each VLAN must have its own independent subnet address. Therefore, in the parameter settings of the backbone switch, the number of subnet Gateway Addresses supported by the VLAN is also an important indicator.

4. Support for more protocols

"One-time routing and multiple-times switching" is the guiding ideology of vswitches for Route switching. However, this three-layer forwarding method is time-consuming for first packet forwarding, especially on backbone layer switches. This forwarding mechanism restricts the forwarding rate. Now, the backbone switch basically uses hardware to implement the maximum matching forwarding mechanism, so that it can process layer-3 forwarding at wire speed. At the same time, the support for the three-tier forwarding table is also an important indicator of the backbone switch. Generally, the number of Route tables supported by the backbone switch and the backbone router is the same. Backbone switches also support a wide range of routing protocols, including RIP, OSPF, IS-IS, and BGP. The support for these routing protocols can fully ensure that backbone switches can run on not only the enterprise network, but also the carrier's junction layer and backbone layer.

5. stream classification and QoS

The support for stream classification and QoS protection are also an important feature of backbone switch parameters. The number of users connected to backbone switches is large, and the network requirements of users are also complicated. Therefore, the backbone switch should be able to provide QoS and Filter Based on stream classification for different users and different network environments. The number of stream categories will greatly affect the business capabilities of backbone switches at the junction points and meet the increasing business needs of users and their security assurance capabilities. Therefore, the current backbone switches should support QoS and bandwidth Assurance Based on stream classification.

6. Higher security requirements

Backbone switches are also different from general switches in terms of security design, and often have higher security and reliability. In terms of design, the manufacturer also tries its best to follow the telecom-level design scheme. For example, the redundant backup design of the power supply, the Dual Backup design of the main control routing board, the hot swapping design of the circuit board without interrupting the business, and the dual backup design of the Network Board. VRRP technology is preferred in backbone switches for high reliability.

7. More centralized network management

In terms of network device management, backbone switches also have their own characteristics. Because backbone switches are often on the operator's network equipment side, the number of access layer devices is large, and the maintenance workload is huge, it is urgent to provide devices with unified management and maintenance measures. Currently, cluster management protocols are generally supported in backbone switch parameters.

In cluster management, a single management IP address can be used to maintain a large number of network devices, and provides various convenient network maintenance methods, such as device topology discovery, device failure and link failure alarms, and unified device configuration, therefore, it has gradually become the main means of network device management.

Ii. Business Characteristics of backbone switches

1. the multicast service will be rapidly developed in the fields dominated by backbone switches.

Although there are still many difficulties to overcome to achieve large-scale multicast applications, the prospect of multicast applications is still optimistic, especially in the case of in-depth development of Ethernet technology and increasing multimedia services, coupled with the emergence of backbone LAN switches, multicast has a huge market potential and has gradually become an indispensable service in broadband networks. As a parallel transmission method with unicast, multicast not only reduces the occupation of network resources, but also improves scalability, it is also convenient to provide some new services by using the multicast feature of the network. With the increasing number of multimedia services in the network, the superiority and importance of multicast become more and more obvious.

2. The three-in-one service will be applied in backbone switches.

With the development of IP technology, it has become possible that voice, data, and video are uniformly carried on the IP network. Especially, VoIP is widely used, and many enterprises and operators use VoIP technology. In traditional networks, voice, data, and video are all carried by independent networks. The cost of network construction is high and the maintenance and management is complex. The three networks are integrated and multiple services are unified in one network, to avoid the disadvantages of network separation.

3. the user management business will develop rapidly

At present, the most urgent task facing operators is how to make the broadband network like the narrowband PSTN service to bring operational, manageable, and value-added features. Therefore, implementing user management is an important service of broadband backbone switches.