Layer-3 switching dominant LAN

Source: Internet
Author: User

Now, the Internet industry is no stranger to the word "layer-3 switching". In medium and large scale network construction, there are no more mainstream network models with gigabit layer-3 switches as the core. In fact, the emergence of layer-3 switching from its emergence to today's widespread application is just a few years ago, the rapid development of the computer network acceleration momentum, it is amazing.
Layer 1 and Layer 2
Looking back at the early stages of the network, when applying LAN technology to networking, it was mainly limited to host connection, file sharing, and print sharing. Multiple users can share 10 Mb/s bandwidth to meet the requirements. As the network scale expands, the network system is no longer competent, because the earliest network interconnection device in the LAN is a hub, which is a layer of equipment. The collision detection and error re-transmission process of user data based on CSMA/CD physical protocol greatly reduces the transmission efficiency. At that time, a two-layer device bridge was used to reduce the network segment and the collision domain, thus optimizing the LAN performance. However, it is a device that is transparent to the upper layer (Layer 3 or above) protocol and cannot effectively prevent broadcast storms. Therefore, a router is required. Vrouters play a key role in subnet interconnection, security control, and broadcast storm restrictions. However, complicated algorithms and low data throughput make vrouters a network bottleneck. Aware of the above problems, the industry has improved the bridge, made a LAN switch, and used it to replace the hub to improve network performance.
A lan switch is a layer-2 network device that constantly collects and creates its own MAC address table during operations and regularly refreshes the table. It enables dedicated bandwidth between network sites, eliminates unnecessary Collision Detection and error re-transmission, and improves transmission efficiency. In addition, user information is transmitted point-to-point, and other nodes are invisible. However, layer-2 switching also exposes its weakness: it cannot effectively solve problems such as broadcast storms, inter-network interconnection, and security control. Therefore, the VLAN Virtual LAN technology on the switch is generated.
Layer-3 switching and VLAN
The emergence of the "layer-3 switching" concept is closely related to VLAN. In fact, a virtual network is a logical subnet. To avoid a broadcast storm caused by broadcasting on a large vswitch, You can further divide it into multiple virtual networks. In a virtual network, information sent by a workstation can only be sent to other sites with the same virtual network number. Other Virtual Network members cannot receive the information or broadcast frames.
As the network becomes more complex and the performance requirements become higher and higher, network administrators are required to successfully deploy VLANs to make the network more flexible and easy to manage. In the past, network administrators spent 3/4 of their time maintaining the network infrastructure, ensuring the optimization of communication traffic, and handling mobile and change work. Generally, when a user moves to another physical location in the network, the network needs to be reconfigured, and even the user's workstation needs to perform a lot of management work. To address this problem, VLAN deployment reduces the resources required for managing network movement and changes, thus saving a lot of valuable resources for users. VLAN technology can also provide users with value in the following key areas:
More cost-effective broadcast control than vrouters, effectively inhibiting broadcast storms.
Supports multimedia applications and efficient multicast control to improve the effective utilization of network bandwidth.
To improve network security, various explicit or implicit VLAN division methods provide policy-based security access mechanisms.
Automated Network Monitoring and Management, more effective network monitoring.
Reduces routing requirements. Based on ASIC Technology, this greatly improves the data packet forwarding capability of devices.
Vro challenges
How do VLANs communicate? The simple answer is "via routing ". Therefore, this technology also raises some new problems: communication between virtual networks is not allowed, which also includes IP Address Resolution (ARP) packets. To communicate, you need to use vrouters to bridge these virtual networks. This is the problem of virtual networks: vswitches are fast but cannot solve the broadcast storm problem. Using Virtual Network Technology in vswitches can solve the broadcast storm problem, however, you must place a vro to connect virtual networks. In this network system integration mode, routers are the core.
In the past, the network was generally allocated according to the "80/20" rule, that is, only 20% of the traffic was communicated with other parts of the central server or enterprise network through the backbone router, 80% of network traffic is still concentrated in subnets of different departments. Today, this proportion has been increased to 50% "evenly divided into autumn") or even 80% to 20/80,), because today's network is experiencing the collective influence of many applications. Network applications have surpassed components and e-mails, and the new applications have quickly and profoundly impacted the network. For example, anyone can access the set Web page through any browser, data Warehouses that support commercial functions such as sales, services, and finance.
This change has a direct impact on traditional routers. Because traditional routers focus more on multiple media types and transmission speeds, data buffering and conversion capabilities are more important than line rate throughput and low latency. The high cost and low performance of a router make it a bottleneck of the network. However, due to the need for interconnection between networks, it is indispensable and at the core of the network. Although high-speed routers have also been developed, they are only used for the backbone of the Internet because of their high cost.
What is layer-3 switching?
In this case, a layer-3 switching technology is proposed. Layer-3 switches are the key to adopting Intranet applications. They combine the advantages of layer-2 switches and layer-3 routers into a flexible solution that provides line rate performance at all levels. This integrated structure also introduces policy management attributes, which not only associate Layer 2 with Layer 3, but also provides traffic prioritization, secure access mechanisms, and a variety of other flexible functions. A layer-3 Switch consists of three layers: LAN interface layer, L2 switching matrix layer, and L3 Switching Matrix routing control.
Traffic implementation on layer-3 switches

With the continuous promotion and application of layer-3 switches in the market, layer-3 switching technology and its products have been widely used in the construction of enterprise networks/Campus Networks and broadband IP networks, such as man and Smart Community access, market demand and Technology Development boost the in-depth development of such applications. Applications of layer-3 switching penetrate into the edge access layer from the initial backbone layer and the aggregation layer in the middle. Different manufacturers are also launching a series of L3 switches with better performance. Generally, these three-layer switching products use programmable and scalable ASIC chip technology and provide the following rich features: different products from different manufacturers or even the same manufacturer, only some of the features can be satisfied or partially satisfied)
No-blocking line rate switching and routing for all network interfaces and protocols on all ports.
High Throughput forwarding packets/second) is usually 10 times faster than that of high-end routers ~ 100 times.
Multi-protocol routing options: ipr1_1/v2, OSPF), IP MulticastDVMRP, PIM), and IPX.
Supports L2/L3 VLAN Division: Port/MAC address/protocol/IP subnet/802.1Q/Cisco ISL.
With reserved bandwidth RSVP) and with CoS and QoS business priority processing, supporting P, DifferServ.
You can set Access List Control filtering rules or firewall-based security policies.
Supports PPPoE, secure user authentication, and billing to enhance user management features.
Supports incremental distribution of Ethernet bandwidth units.
ASIC's programmability supports technologies such as IPv6 and other future technologies to protect user investment.
Where is layer-3 switching used?
The application of a layer-3 switch is actually very simple. It is mainly used to replace a traditional router as the core of the network. Therefore, all areas that require no WAN connection and require a router can be replaced by a layer-3 switch.
In the enterprise network and teaching network, layer-3 switches are generally used in the core layer of the network, and different subnets or VLANs are connected using the Gigabit or M ports on the layer-3 switch. Because of its relatively simple network structure, the number of nodes is relatively small. In addition, it does not require many control functions and requires low costs.
In the current hot broadband network construction, layer-3 switches are generally placed in the center of the residential area and the Convergence layer of multiple residential areas. The core layer generally uses high-speed routers. This is because network interconnection is only one requirement in the construction of a broadband network, because the user requirements in the broadband network are different, so more control functions are required, this is the weakness of a layer-3 switch. Therefore, the core of the broadband network is generally high-speed routers.

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