Differences between vswitches 1, 2, and 3

When purchasing a layer-3 Switch, pay attention to the following points: first, its hardware equipment. A good hardware equipment is the primary guarantee for the entire operating environment, the second is the main technical parameter of vswitch performance, which also affects its service life.

The development of L2 Switch Technology is relatively mature. L2 Switch is a data link layer device that can identify the MAC address information in the data packet and forward it according to the MAC address, the MAC addresses and corresponding ports are recorded in an internal address table.

The specific workflow is as follows:

(1) When the switch receives a packet from a port, it first reads the source MAC address from the packet header, so that it knows the port on which the machine with the source MAC address is connected;

(2) read the target MAC address in the header and find the corresponding port in the address table;

(3) If the table contains a port corresponding to the destination MAC address, copy the data packet directly to the port;

(4) If no corresponding port is found in the table, the packet is broadcast to all ports. When the target machine responds to the source machine, the switch can learn which port the target MAC address corresponds, the next time you transmit data, you no longer need to broadcast all ports. In this process, the MAC address information of the entire network can be learned. The second-layer switch creates and maintains its own address table.

The working principle of a L2 Switch can be inferred from the following three points:

(1) because the switch exchanges data on most ports at the same time, it requires a wide switching bus bandwidth. If the L2 Switch has N ports, the bandwidth of each port is M, if the bandwidth of the vswitch bus exceeds N × M, the vswitch can achieve line rate switching;

(2) the MAC address of the machine connected by the Learning port, write the address table, and the size of the address table (two common expressions: one is beffer ram, and the other is the MAC Table value ), the address table size affects the access capacity of the vswitch;

(3) Another layer-2 switch generally contains an ASIC (Application specific Integrated Circuit) chip used to process packet forwarding, so the forwarding speed can be very fast. Because different manufacturers use different ASIC, the product performance is directly affected.

The above three points are also the main technical parameters used to judge the performance of Layer 2 and Layer 3 switches. Please pay attention to the comparison when considering device selection.

Layer-3 Switching

For example, if A wants to send data to B and the target IP address is known, A uses the subnet mask to obtain the network address and determine whether the destination IP address is in the same network segment as itself. If A is in the same network segment but does not know the MAC address required for data forwarding, A sends an ARP request, B returns its MAC address, and A uses this MAC encapsulation packet to send it to the switch concurrently, the second-layer switch module is used to find the MAC address table and forward data packets to the corresponding port.

If the destination IP address is not displayed in the same CIDR block, A needs to communicate with B, and there is no corresponding MAC address entry in the stream cache entry, send the first normal data packet to a default gateway. This default gateway is usually set in the operating system and corresponds to the layer-3 routing module. Therefore, we can see that for data not in the same subnet, the MAC address of the default gateway is first placed in the MAC table;

Then, the layer-3 module receives the packet and queries the route table to determine the route to B. A new frame header is constructed, with the MAC address of the default gateway as the source MAC address, the target MAC address is host B's MAC address.

Through A certain identification trigger mechanism, it establishes the MAC address and forwarding port correspondence between host A and host B, and records the data from host A to host B in the stream cache entry table, it is directly submitted to the layer-2 Switching Module. This is generally referred to as one-time route forwarding.

The above is a brief summary of the three-layer switch process. We can see the characteristics of the three-layer switch:

(1) hardware is combined to achieve high-speed data forwarding. This is not a simple superposition of Layer 2 switches and routers. The Layer 3 routing module is directly superimposed on the Layer 2 switching high-speed backplane bus, breaking through the interface speed limit of traditional routers, the speed can reach dozens of Gbit/s. Calculating the backboard bandwidth is two important parameters for the performance of a layer-3 switch.

(2) Concise routing software simplifies the routing process. Most of the data forwarding, except for the necessary route selection, is handled by the routing software, and is a layer-2 module for high-speed forwarding. Most of the routing software is an efficient optimization software that has been processed, it is not a simple copy of the software in the router.

Selection of L2 and L3 Switches

L2 switches are used in small local networks. There is no need to talk about this. In a small LAN, broadcast packets have little impact, the two-layer switch's fast switching function, multiple access ports, and low price provide a perfect solution for small network users.

The advantage of a vro lies in its rich interface types, powerful three-tier functions, and powerful routing capabilities. It is suitable for routing between large networks. Its advantage lies in the selection of the best route and load balancing, router functions such as link backup and exchange of route information with other networks.

The most important function of a layer-3 switch is to accelerate the fast data forwarding within a large local area network. If a large network is divided into small local networks by department, region, and other factors, this will lead to a large number of Internet exchanges. Simply using a layer-2 switch cannot achieve Internet mutual access;

For example, simply using a vro, because of the limited number of interfaces and slow route forwarding speed, the network speed and network scale will be limited, and adopting a layer-3 switch with the routing function for fast forwarding will become the first choice. In general, in a network with a large volume of intranet data streams that require fast response forwarding.

If a layer-3 switch is used to do this, the layer-3 switch will be overloaded, and the response speed will be affected. routes between networks will be handed over to the router to make full use of the advantages of different devices, it is a good networking strategy. Of course, the premise is that the customer's pockets are very busy. Otherwise, they will leave for the second place, so that layer-3 switches can also be connected to the Internet.

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