Layer-3 Switching Technology and Its Application in VLAN subnet planning (1)

In the traditional campus network mode, network interconnection is generally a multi-level switch connected to one or more trunk switches. The switches communicate with each other through routers, traditional routers work at the network layer of the OSI model and perform route computing and packet forwarding based on software. With the expansion of campus network, the increase of users, and the rapid development of various IP-based applications such as video conferencing and distance education, traditional routes are increasingly becoming a bottleneck in campus network security management and traffic control, while traditional switches have fast processing capabilities. However, it is essentially a multi-port bridge that inevitably produces broadcasting and cannot implement routing. To solve this conflict, network vendors have proposed the idea of layer-3 switching.

Working Principle and functions of layer-3 Switching Technology

A traditional router works at the network layer of the OSI Layer-7 model. When it receives any packet, including a broadcast packet, it removes the information on the layer-2 data link layer of the packet, view information on the third layer. Then, determine the route of the data packet based on the route table, encapsulate the second layer of information, and finally forward the data packet. The bottleneck of a router is that it is a connectionless device and its working mechanism makes it a forwarding and forgetting network device. Even all data packets sent from the same source address to the same destination address must repeat the same routing process, which makes it impossible for the router to have a high throughput. In addition, the complex processing and powerful functions of a router are mainly implemented by software, which inevitably makes it a network bottleneck.

With the development of the routing technology, the exchange technology, which is one of the solutions for network transmission bandwidth, has developed rapidly. The exchange network is a network system centered on switches. The network switches and multi-port bridges are very similar because they all work at the data link layer. When the network switches transmit data between different ports, they are also the destination MAC address based on data packets. The realization of a vswitch usually adopts a full hardware structure and is fast, but it does not have the ability to isolate broadcast data packets like a bridge.

L3 switching technology (LAYER3SWITCHING) is an emerging network interconnection technology that integrates the advantages of the above two technologies, also known as layer-3 switching technology. If you only consider IP, it is called IP exchange technology. The layer-3 Exchange router integrates an ASIC chip for the routing processing function based on the dedicated packet forwarding function. It combines the high-speed forwarding of the traditional layer-2 switch with the router routing function, the implementation of line rate routing solves the bottleneck of the router. There are two types of L3 switching technology solutions: Core-based and edge-Based Multi-layer Hybrid Switching. The former represents cisco's netflow switching and tagswitching switching, emphasizing the speed of the switch core layer, and completely using ASIC hardware to achieve routing and switching at line speed, the latter represents the fast ip of 3com, and the virtual fast Security Network of cabletron. The method used is to route the network at the first layer, then, the second layer switches the end-to-end network stream data group. This is the policy of "one route, then switch.

The powerful functions of the layer-3 Exchange router are as follows:

1) routes are calculated based on the L3 protocol. The supported routing protocols include r1_1, V2, and OSPF.

2) supports IGMP, DVMRP, and other common IP multicast protocols. When a vro receives a multicast packet, it first forwards the packet to the VLAN that contains the multicast group members, then, the packet is forwarded to the port of the multicast group member.

3) Quality of Service Q OS: the packets are given a specific priority. packets with different priorities are sent to different queues for forwarding.

4) supports standard SNMP Network Management Protocols and traditional command line interface (CLI ).

5) Multiple partitioning policies for virtual networks. In particular, they not only support traditional port-based VLAN division, but also support VLAN division based on IP addresses, subnet numbers, and protocol types, this brings great convenience to campus network management.

Therefore, the new layer-3 Exchange router is used as the main device in the LAN of the campus and building. In addition to providing high bandwidth for packet forwarding and the above functions, it also provides security, monitoring, management, and Configuration Services.