Fully explore the choice and use of Ethernet Switches

Ethernet switches are still commonly used. So I studied the selection and use of Ethernet switches. Here I will share with you, hoping to help you. Recently, when I opened a route for a new Internet cafe, the administrator of the Internet cafe ran to ask me whether to select a HUB for Computer Interconnection in the internet cafe or an Ethernet switch, is CISCO's Ethernet switch the best. People often say that the right option is not expensive.

But how to choose is right? Common Small and Medium networks have 200 or 300 computers, and more than computers. They are connected through the Integrated Wiring System switching device. Connect to the broadband network through an Ethernet switch or router. Therefore, the selection and use of various Ethernet switches will have an extremely important impact on the performance of the broadband network system. I will discuss some common Ethernet switch problems at work.

I. Differences between hubs and switches

1. A hub (only a non-Switched Single Network Segment and multi-network segment) belongs to the first layer of the OSI physical layer device in the OSI architecture, while an Ethernet switch belongs to the second layer of the OSI data link layer device, currently, layer-3 switches provide VLAN and IP-based routing and switching functions on the layer-2 platform, while layer-4 switches are port-based applications. The hub only plays a role in synchronization, amplification, and shaping of data transmission. It cannot effectively process short frames and fragments in data transmission, and cannot guarantee the integrity and correctness of data transmission, similar to a large bus LAN, an Ethernet switch can synchronize, zoom in, and shaping data transmission, and filter short frames and fragments to forward encapsulated packets.

2. according to the working method, the hub is a broadcast mode. That is to say, when a port of the hub is working, all other ports can listen to the information, which may lead to a broadcast storm, in addition, only one port sends data at a time, and the security is poor. All NICs can receive the sent data, but the non-destination Nic discards the packet. When an Ethernet switch works, only the requested port and the destination port respond to each other without affecting other ports. Therefore, the switch can isolate the conflict domain and effectively suppress the generation of broadcast storms.

3. from the bandwidth perspective, no matter how many ports the hub has, all ports share a bandwidth. At the same time, only two ports can be used to transmit data, while other ports can only wait, at the same time, the hub can only work in half duplex mode. For a vswitch, each port has an exclusive bandwidth. When the two ports work, other ports are not affected, at the same time, the switch can not only work in half duplex mode, but also in full duplex mode.

4. vswitches work on the data link layer to address MAC addresses, with additional addressing overhead. In the case of low data traffic, the latency may be greater than the data transmission time; the hub works in the physical layer to transmit data in broadcast mode, and the low traffic performance is not suitable for LAN with shared bus architecture.

Ii. Differences between layer-2 switching and layer-3 switching and Routers

Layer 2 exchange technology works at the data link layer. It forwards the MAC address of the received packet to the corresponding port in the internal address table, and records the MAC address and corresponding port of the packet in the internal address table, if the MAC address is not in the table, broadcast and wait for a response. Therefore, L2 switches have the MAC address learning function, which is transparent to the network layer or high-level protocols. Data Exchange relies on ASIC (dedicated Application Integration chipset) for Dedicated Packet forwarding. However, it cannot process protocols with three or more layers, nor exchange data between subnets of different IP addresses.

Layer-3 switching works on the layer-3 layer in the OSI Layer-7 model. It uses the IP packet header information in the layer-3 protocol to mark the subsequent data streams and reorganize the frame headers, exchange packets with the same labeled data streams to the data link layer to provide a data channel between the target address and the source address. Therefore, the layer-3 switch can determine the route without unpacking, so that data packets can be directly forwarded for data exchange. In this way, IP packets of different subnets can be exchanged. In addition, the layer-3 routing module is not a simple superposition of layer-2 switches and routers. It is composed of layer-3 routing modules. layer-2 switching high-speed backplane bus speeds up to Gbit/s, most of the data that must be processed by the routing software is forwarded to the Third-layer forwarding, while the rest are layer-2 high-speed forwarding.

The router works at the Layer 3 network of OSI. The working mode is similar to that of Layer 2. The router determines the optimal route and forwards data packets. There is a route table in the router, which records various link information for the routing algorithm to calculate the optimal route to the destination. The router then forwards data. If you do not know the target route, discard the packet and return information to the source address. Routers can learn route information from each other or broadcast their own link status, so that route information is updated in a certain way, so that the algorithm can calculate the optimal route. Therefore, the router path computing workload is huge. Generally, a vro has a limited number of ports and the route forwarding speed is slow. When the intranet data traffic is large and fast response is required, it is often recommended to use a layer-3 switch, and the inter-network routing work is handed over to the router.

Iii. Switch classification and selection indicators

From the perspective of transmission media and transmission speed, LAN switches can be divided into Ethernet switches, Fast Ethernet switches, Gigabit Ethernet switches, FDDI switches, ATM switches, and wildcard ring switches, these switches are applicable to Ethernet, fast Ethernet, FDDI, ATM, and ring-based network.

According to the most common classification method, LAN switches can be divided into Desktop switches, Workgroup switches, and Campus network switches. According to the architecture characteristics, Ethernet switches are also divided into three types: rack-mounted, fixed configuration with expansion slot, and fixed configuration without expansion slot.