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What is a Layer 3 switch, the origin of Layer 3 switching technology, Layer 3 switches, and application examples of Layer 3 switching. Gain an in-depth understanding of Layer 3 switch technology.
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1. The origin of the three-layer switching technology
Layer 3 switching, also known as multi-layer switching or IP switching, is a network device that combines transmission switches and traditional routers. It can not only complete the port switching function of traditional switching Yang, but also complete the road functions of some routers.
The traditional switching technology operates on the second layer (data link layer) in the OSI reference model, and it continuously collects information to build its own MAC address table during operation. When the switch receives an Ethernet frame, it checks the destination MAC address of the Ethernet frame and checks the MAC address table to confirm from which port the packet should be sent out. But when the switch receives a frame whose destination address is not in the MAC address table, the switch will "diffuse" the packet, that is, send it out from all ports, just like the switch receives a broadcast packet, which exposes the traditional The weakness of the LAN switch: it cannot effectively isolate the broadcast packets, which reduces the effective bandwidth utilization of the network. If there are too many broadcast packets to a certain extent, a broadcast storm may be formed and the network will be paralyzed. Therefore, the VLAN technology on the switch has been produced. However, data transmission between VLANs needs to be realized through routers, and routers have become key devices in the network.
The traditional routing technology operates on the third layer (network layer) of the OSI reference model, and its core functions mainly include data packet forwarding and routing processing. The data message forwarding function is mainly to transmit data messages between subnets, including checking the header of IP data packets, segmenting and reassembling IP data packets, modifying the time to live (TTL) parameters, and recalculating the header checksum of IP data packets. , MAC address resolution, etc.; routing processing sub-functions include creating and maintaining routing tables, which need to use routing protocols such as RIP or OSPF to establish and form routing tables. Once the routing processing is completed, it is the task of the message forwarding sub-function to send the data message to the destination address. The weakness of the traditional router is: the router is a network device that forwards
and forgets, and any data packet must go through the above-mentioned complicated "dismantling" process, even if the data packet sent from the same source address to the same destination address, the same process must be repeated. the process of. At the same time, the complex processing functions of routers are mainly realized through software, which also determines that routers become an insurmountable bottleneck in LAN communication.
Then, how to effectively solve the problem of "when routing between subnets, the bandwidth and speed of the exchange are still used to transmit data"? Three-layer switching technology came into being. Layer 3 switching combines the advantages of Layer 2 switches and Layer 3 routers into an organic whole. The emergence of three-layer switching technology not only solves the situation that the subnets in the network segment must rely on routers for management after the division of network segments in the LAN, but also solves the network bottleneck problem caused by the low speed and complexity of traditional routers. Simply put, Layer 3 switching technology is "Layer 2 switching + Layer 3 forwarding".
2. Implementation of Layer 3 switching technology
Because the three-layer switching technology is not a standardized technology, the three-layer switching equipment of different manufacturers adopts different technical implementation methods. Listed below are several widely used three-layer switching technologies.
(1) 3Com's Fast IP
This technology adopts the strategy of "routing once, switching later", and its technical basis is Next Hop Resolution Protocol (NHRP, Next Hop Resolution Protocol). Both the source host and the destination host need to run the Fast IP protocol. When exchanging, the source host must first initialize a standard IP communication process, and the source host sends a Fast IP connection request, which is like an ordinary data message The same route goes through the network, if the destination host also runs the Fast IP protocol, then return an NHRP reply containing the MAC address, if there is an exchange path between the two, then exchange, otherwise continue routing.
(2) 3Com's FIRE
Known as a flexible and intelligent routing engine, FIRE uses ASIC (Application Specific Integrated Circuit) to implement third-layer routing and forwarding at wire speed. It is an innovative integrated Internet interconnection architecture. The technology provides a wide range of Layer 2 and Layer 3 functions and provides intelligent self-taught network control capabilities, including network security, optimized traffic handling, bandwidth pinning and QoS.
(3) Cisco NetFlow
This technology is an improvement on the traditional routing and forwarding technology. The basic principle is: the first data packet is still forwarded using the traditional layer-3 routing method. After forwarding, the layer-3 switch records the information of the first data packet in the NetFlow cache, and the subsequent data packets arrive first. Perform matching search in CACHE, if hit, use the routing information cached in CACHE to forward directly, otherwise, perform routing.
(4) Cisco's label switching
This technique is to add a mark to the data packet when forwarding. A tag is a short label with a fixed length, and each tag can identify the aggregation of one or more paths. The routing table uses markers for routing table lookups, rather than traditional subnet prefixes, and a domain is removed every time a marker passes through a router, similar to the basic principle of a postal code. The distribution of tags is realized by means of Tag Distribution Protocol (TDP, Tag Distribution Protocol).
3. Application of Layer 3 switching technology
Although it has only been a few years since the introduction of the three-layer switching concept to its popular application today, it is more and more widely used in network construction. Layer 3 switches have pushed routers to the edge of the network due to their advantages of fast speed, good performance, and low price. Where there is no need for WAN connection and routers are needed, Layer 3 switches can be used instead. Just as routers dominate the wide area network, it is an indisputable fact that the three-layer switching layer is gradually moving towards the dominance of the local area network. Especially for LANs that require VLAN division, Layer 3 switching is the best choice.
A typical application of a Layer 3 switch is shown in the figure. This is a LAN with a three-level switching structure, in which the backbone switch is a 1000Mbps three-layer switch, which supports full-duplex switching, intelligent network management and various forms of VLAN division. It can be used to divide logical subnets with different functions, and Centralized control and management of the entire network through the network management system, including monitoring and adjusting the operating status of the network, statistics of online information flow and user usage, etc. Devices that can be directly connected to the backbone switch include routers, various servers, central workstations, and secondary switches. 100Mbps Layer 2 switch can be selected as the ground-level switch, the uplink interface is 1000Mbps, and supports VLAN and SNMP. The super-large-scale switches can use ordinary layer 2 switches or hubs.
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The above is what I want to talk about today. This article mainly introduces what is three-layer switching and the practical application of three-layer switching technology. I also look forward to sharing more with you. Handsome guys and beauties give me a thumbs up. Let's work together in 2023! ! !