Important Functions of layer-3 switches

Layer-3 switching is the key to adopting Intranet. It combines the advantages of layer-2 switches and layer-3 routers into a flexible solution to provide line rate performance at all levels. This integrated structure also introduces policy management attributes.

It not only associates Layer 2 with Layer 3, but also provides traffic priority processing, security, and a variety of other flexible functions, such as link aggregation, dynamic deployment of VLAN and Intranet. Layer-3 switches are divided into three parts: interface layer, switch layer, and route layer.

The interface layer includes all important LAN interfaces: 10/100 M Ethernet, Gigabit Ethernet, FDDI, and ATM. The switching layer integrates multiple LAN interfaces with policy management. It also provides link aggregation, VLAN, and Tagging mechanisms.

The routing layer provides the main LAN routing protocols: IP, IPX, and AppleTalk. Through policy management, the routing layer provides the traditional routing or pass-through layer-3 forwarding technology. Policy management and administrative management enable the network administrator to adjust the network according to the specific needs of the enterprise.

Compared with Layer 3, the level 2 Adoption determines the so-called network control classification. A pure Layer 2 solution is the cheapest solution, however, it provides the least control over subnet division and broadcast restrictions. Layer-3 switches provide dynamic integration support for all levels in the classification.

Traditional general-purpose routers and external switches can also achieve this goal. However, compared with this solution, layer-3 switches require less configuration, less space, and less wiring, cheaper and more reliable performance.

A layer-3 Switch has all the functions of a traditional switch. The layer-3 Switch prevails. The specific technical implementation of the switch includes:

1. Programmable ASIC
ASIC is a dedicated Integrated Circuit dedicated to optimizing Layer 2 processing. It is the core of today's networking solutions and integrates multiple functions on one chip, it has the advantages of simple design, high reliability, low power consumption, higher performance and lower cost.

2. Distributed Pipeline
With the distributed pipeline, multiple distributed forwarding engines can quickly send data packets independently. In a single pipeline, multiple ASIC chips simultaneously process multiple frames. This concurrency and pipeline improves the forwarding performance to a new level: On-Demand Unicast, Broadcast, and Multicast on all ports.

3. dynamically Scalable Memory
For advanced LAN switching products, the real performance is built on an intelligent storage system. The layer-3 Switch directly associates a portion of the memory with the forwarding engine. More interface modules are added, including their respective forwarding engines, and memory is also expanded accordingly. It also uses streamlined ASIC processing to dynamically construct the cache, which increases the memory usage. The system can also handle large burst data streams without packet loss.

4. Advanced queue mechanism
Even if the network device has outstanding performance, it will be damaged by the congestion on the connected network segment. Traditionally, the traffic through a port must be stored in the cache of only one output queue. No matter how high its priority is, it must also be processed in the first-in-first-out mode.

When the queue is full, any excess parts will be discarded. In addition, when the queue grows, the latency also increases. This feature makes it very difficult to run real-time transaction processing and multimedia applications on Traditional Ethernet. For this reason, many network device manufacturers have developed new technologies that provide different service levels on an Ethernet segment and control latency and jitter at the same time.

In this way, we have introduced a queue mechanism with different levels for each port, which can better distinguish different traffic levels in order to match the network closer to high-performance applications. Data packets such as multimedia and real-time data streams are put into high-priority queues.

The Weighted Fair queuing algorithm can be used to manage high-priority queues more frequently, but it does not ignore low-priority queues. Users of traditional applications do not notice changes in response time and throughput, while those who use emergency applications receive timely responses.

5. Automatic traffic classification
Some data streams are more important than other data streams. With Automatic traffic classification, the layer-3 switch can instruct the data packet assembly line to differentiate user-specified data streams to achieve low-latency, high-priority transmission, and avoid congestion.

6. Intelligent permission Control
The layer-3 Switch provides multiple security mechanisms and uses a traffic classifier. administrators can restrict any identified data streams, including restricting access to servers and eliminating useless protocol broadcasts. This is a breakthrough in the network technology field, that is, providing a line rate firewall.

7. Dynamic Traffic Monitoring
Traffic classification, priority processing, and resource retention enable enterprise network and Intranet administrators to focus on more important things, that is, traditional and next-generation applications. But one thing still needs to be done is traffic monitoring. Traffic monitoring is not a policy mechanism because it is actually a protection mechanism.

It monitors traffic and network congestion conditions and responds dynamically to these conditions to ensure that all network elements end users and networks themselves are under control and can run best. Many layer-3 switches use the IEEE 802.1p service level for priority processing on congested LAN.

To avoid congestion, the high-performance Layer-3 Switch even uses more advanced technologies to dynamically monitor the size of the output queue, so as to detect whether a port will become congested. By controlling the queue size and congestion, the network can maintain the limit required for latency-sensitive data streams.

8. scalable RMON implementation
RMON support has become an indispensable part of active and extensive network management. The MIB defined in RFC 1757 contain statistics on the physical layer and MAC layer. The RMON 2 defined in RFC 2021 extends the collection of statistics to the network layer.

9. Vector Processing Technology
Vector processing technology is used to accelerate the processing speed of data frames. The architecture of the layer-3 Switch not only adds the control capability of the layer-3 on the layer-2, but also adds multi-faceted vector control, thus greatly enhancing the vector processing function. Layer-3 vswitches have many advantages in vector processing:

◆ Fast Frame processing speed. With ASIC-based data packet classification, forwarding, and interpretation technologies, frame decoding by software is minimized, this method can achieve much higher performance.
◆ Highly adaptive function control. Vector processing works with programmable ASIC to support future standards with minimal overhead. For example, IPv6 support is already part of Vector Logic.
◆ Enhanced management functions. Multidimensional vector processing also includes built-in Network Management Agents and RMON.

10. multi-chip CPU
In highly reliable vswitches, a dedicated high-performance RISC processor is absolutely required. In fact, the combination of frame Processing Unit (FP) and Vector Logic provides unparalleled performance. An independent application processor AP) can assist FP. Like FP, AP is also a high-performance CPU.

AP controls all operations except Frame Forwarding: High-Level bridging and routing, such as Spanning Tree and OSPF protocols, as well as SNMP and HTTP operations. The advantage of using AP and FP is obvious, because management and computing work does not affect data forwarding, thus achieving high throughput and low latency.

Through the above technical analysis, we can easily see that high performance, security, ease of use, manageability, stackability, service quality and fault tolerance are the technical features of the current switch. As video conferencing, real-time multicast, network calls, program-controlled switching, and automatic call forwarding show the emergence of a new generation of applications in the multimedia era.

Where should exchange technology develop? It is certain that high bandwidth, security, service quality, and intelligence should be the technical direction pursued by the next generation switch. However, it is worth mentioning that some manufacturers are moving towards Distributed Network Computing of switches.

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