(CCNP exchange
Cisco switch cluster technology
For the connection between switches, there should be two familiar types: one is stacking, and the other is cascade connection. The cascade connection method is easy to cause bottlenecks between switches. Although the stacking technology can increase the backplane speed and eliminate the bottleneck of connections between switches, it is greatly limited by the distance and the number of switches.
The switch cluster technology introduced by Cisco can be regarded as a combination of stacking and cascade technology. This technology can logically combine switches distributed in different geographical ranges, and can be managed uniformly. The specific implementation method is to select a commander in the cluster, while other switches are in a subordinate position and managed by the commander. For the new catalyst3500xl series, the three models of catalyst3512xl, catalyst3524xl and catalyst3508gxl can become the commander. For the managed 2900 and 1900 series, they can join the switch cluster. The latest Cisco switch cluster technology is used to improve the traditional stacking technology to a new level. It is said that the 2900xl series can also be a commander.
This series of products is aimed at medium-sized enterprises and institutions. While providing high performance and low cost, it reduces the complexity and is easy to integrate into the existing network. It allows network administrators to use the standard web explorer. Geographically dispersed switches are managed from anywhere on the network through a single IP address.
Specific examples are as follows:
Suppose that the network center adopts Cisco's catalyst6506 switch, and the cluster commander adopts catalyst3508gxl. Between the cluster commander and the central switch, Gigabit connection or 4 Gigabit connection can be realized through GEC, while the combination of 3500, 2900 and 1900 is used within the cluster, and the connection between them is through FEC. Then assign an independent IP address to the cluster to manage the whole cluster.
The switch cluster technology supports up to 16 switches and can provide up to 16
48 ports.
Switch backplane bandwidth
Backplane bandwidth is the maximum amount of data that can be handled between the switch interface processor or interface card and the data bus. The higher the backplane bandwidth of a switch, the stronger the data processing capacity it can handle, but at the same time, the design cost will rise.
However, how can we check whether the backplane bandwidth of a switch is sufficient? Obviously, the estimation method is useless. I think it should be considered from two aspects:
1. ) the sum of the capacity of all ports x the number of ports should be less than the backplane bandwidth. Full duplex non blocking switching can be realized, which proves that the switch has the conditions to maximize the data exchange performance.
2. ) full configured throughput (MPPs) = full configured Ge ports × 1.488mpps the theoretical throughput of one Gigabit port when the packet length is 64 bytes is 1.488mpps. For example, a switch that can provide up to 64 Gigabit ports should have a full configured throughput of 64 × 1.488mpps=95.2mpps can ensure non blocking packet switching when all ports work at average wire speed. If a switch can provide 176 Gigabit ports at most and the declared throughput is less than 261.8mpps (176x1.488mpps=261.8), users have reason to think that the switch adopts a blocking structure design.
Generally, the switch that meets both requirements is the qualified switch.
The switch with relatively large backplane and small throughput retains the ability to upgrade and expand, but there is a problem with software efficiency / special chip circuit design; The backplane is relatively small. Switches with relatively large throughput have relatively high overall performance. However, the backplane bandwidth can be trusted by the manufacturer's propaganda, but the throughput cannot be trusted by the manufacturer's propaganda, because the latter is a design value, the test is very difficult and of little significance.
The backing rate of the switch is generally Mbps, which refers to the second layer. Only MPPs is used for switches above the third layer
Comparison between layer 3 switch and router
In order to meet the challenges brought by the deepening of network application, the network is developing rapidly in both scale and speed. The speed of LAN has been increased from 10mbit/s to 100mbit/s. At present, Gigabit Ethernet technology has been widely used. In terms of network structure, it has also developed from the early LAN with shared media to the current switched LAN. Switched LAN technology makes the special bandwidth available to users, which greatly improves the efficiency of LAN transmission. It can be said that in the technology of network system integration, the layer 1 interface and layer 2 switching technology directly facing users have been satisfactorily answered. However, as the core of the network, the router technology which plays the role of interconnection between networks has no qualitative breakthrough. In this case, a new routing technology came into being, which is layer 3 switching technology: it is a router, because it can operate in the third layer of the network protocol. It is a routing understanding device and can play the role of routing decision; It is said that it is a switch because its speed is so fast that it almost reaches the speed of layer 2 switching. Which of the three technologies, layer-2 switch, layer-3 switch and router, is better or worse, and what environment are they applicable to? In order to answer this question, let's start with the working principle of these three technologies
1. layer 2 switching technology
The layer-2 switch is a device in the data link layer. It can read the MAC address information in the data packet and exchange according to the MAC address. There is an address table inside the switch, which indicates the corresponding relationship between MAC address and switch port. When a switch receives a packet from a port, it first reads the source MAC address in the packet header, so that it knows which port the source MAC address machine is connected to. It then reads the destination MAC address in the packet header and finds the corresponding port in the address table. If there is a port corresponding to the destination MAC address in the table, it copies the packet directly to the port, If the corresponding port is not found in the table, the data packet is broadcast to all ports. When the destination machine responds to the source machine, the switch can learn which port the destination MAC address corresponds to. It is no longer necessary to broadcast all ports when the next data transmission. This is how a layer-2 switch establishes and maintains its own address table. Since the layer-2 switch generally has a wide switching bus bandwidth, it can exchange data for many ports at the same time. If the layer-2 switch has N ports, the bandwidth of each port is m, and its switch bus bandwidth exceeds n × M. Then the switch can realize line speed switching. The layer-2 switch does not restrict broadcast packets and copies broadcast packets to all ports.
Generally, layer-2 switches contain ASIC (applicationspecificintegratedcircuit) chips specially used to handle packet forwarding, so the forwarding speed can be very fast.
2. routing technology
The router operates in the network layer, the third layer in the OSI seven layer network model. There is a routing table inside the router, which indicates where to go if you want to go to a certain place. The router receives a packet from a port. It first removes the packet header of the link layer (unpacking), reads the destination IP address, and then looks up the routing table. If it can determine where to send the next step, it adds the packet header of the link layer (packaging) to forward the packet; If the next address cannot be determined, a message is returned to the source address and the packet is discarded.
Routing technology and layer-2 switching look a bit similar. In fact, the main difference between routing and switching is that switching occurs in layer-2 (data link layer) of the OSI reference model, while routing occurs in layer-3. This difference determines that routing and switching need to use different control information in the process of transmitting data, so the ways of realizing their respective functions are different.
Routing technology is actually composed of two basic activities, namely, determining the optimal path and transmitting packets. Among them, the transmission of data packets is relatively simple and direct, while the determination of routing is more complex. The routing algorithm writes various information in the routing table. The router will select the best path according to the destination to which the packet is to arrive and send the packet to the next router that can reach the destination. When the next router receives the packet, it will also check its destination address and continue to transmit it to the following routers using an appropriate path. And so on until the packets reach the final destination.
Routers can communicate with each other and maintain their own routing tables by transmitting different types of information. The routing update information mainly refers to such information, which is generally composed of some or all routing tables. By analyzing the route update information sent by other routers, the router can master the topology of the whole network. Link state broadcast is another kind of information transmitted between routers. It can notify other routers of the link state and progress of the information sender.
3. layer 3 Switching Technology
A device with layer 3 switching function is a layer 2 switch with layer 3 routing function, but it is an organic combination of the two, and it is not simply superimposing the hardware and software of the router device on the LAN switch.
From the perspective of hardware, the interface modules of the layer 2 switch exchange data through the high-speed backplane / bus (the rate can be as high as tens of gbit/s). In the layer 3 switch, the layer 3 routing hardware module related to the router is also plugged into the high-speed backplane / this data contains the following accessories:
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