What Are the Differences Between Layer 3 and Layer 2?

Inside; Layer 3 networks need to use IP routes to implement cross-network segments.

can span multiple conflict domains;

2. The networking capability of the layer 2 network is very limited, and it is generally only a small local area network; Layer 3 networks can be used to form large networks.

3. The Layer 2 network is basically a security domain, that is to say, in the same Layer 2 network, the security of the terminal is basically the same from the network, unless there are other special security measures; A Layer 3 network can be divided into multiple security domains that are relatively independent.

4. Many technologies are relatively used in the Layer 2 LAN, such as DHCP, shared connections provided by Windows, etc., if you need to use them on the Layer 3 network, you need to consider the support of other devices (such as through DHCP relay**.

etc.), etc.) or by other means.

In the selection of enterprise network structure, there are two options: Layer 2 network and Layer 3 network structure.

Here, the second and third layers are classified according to the seepage logic topology, which does not mean that the data link layer and network layer in the ISO seven-layer model, but refers to the core layer, aggregation layer and access layer, which are all deployed in the three-layer network structure, and the second-layer network structure does not have an aggregation layer.

Only the core layer and the access layer of the layer two network structure mode is easy to operate, the switch according to the MAC address table for the packet, if there is a **, if not, then flood, that is, the packet broadcast is sent to all ports, if the destination terminal is late to give a response, then the switch can add the MAC address to the address table, this is the process of the switch to establish the MAC address, but so frequently broadcast the packets of the unknown MAC destination, The network storm formed in the large-scale network architecture is very large, which also greatly limits the expansion of the scale of the layer 2 network, so the networking capacity of the layer 2 network is very limited, so it is generally only used to build a small local area network.

Unlike the Layer 2 network structure, the Layer 3 network structure can form large networks.

Therefore, in the entire three-layer network structure, the equipment requirements of the core layer are the highest, and it must be equipped with high-performance data redundancy transfer equipment and load-balancing equipment to prevent overload, so as to reduce the amount of data that each core layer switch needs to carry. (High-speed switching backbone of the network).

The aggregation layer is the core layer that connects the network and the application layer of each access, and plays the role of "media transmission" between the two layers. The aggregation layer should have the following functions: implement security functions (VLAN division and ACL configuration), overall workgroup access function, and virtual network filtering function.

Therefore, Layer 3 switches should be used for aggregation layer devices. (Provides policy-based connectivity).

The access layer is mainly object-oriented to end customers and provides access functions for end customers. (Connect the workstation to the network).

Layer 2 networks can communicate only through MAC addressing, but only within the same collision domain; Layer 3 networks need to communicate across network segments through IP routes, which can span multiple conflict domains.

The Layer 3 switch can replace the router to a certain extent, but it should be clearly realized that the most important purpose of the Layer 3 switch is to speed up the data exchange within the large LAN, and the routing function is mostly around this purpose, so his routing function is not as strong as the professional router of the same grade, and there are still many deficiencies in security, protocol support, etc., and it cannot completely replace the router.

In the process of practical application, the typical practice is: the interconnection of various subnets in the same LAN and the routing between VLANs in the LAN are replaced by three-plex wide-layer switches, and only when cross-regional network access is to be realized between the LAN and the public network interconnection, the professional router is passed.

Layer 2 and Layer 3 are two different computer network architecture systems. Among them, Layer 2 networking is a network system based on physical addresses, while Layer 3 networking is a network system based on logical addresses. These two networking methods have their own advantages and disadvantages, and enterprises can choose according to their own needs and actual conditions.

Layer 2 networking is a type of networking based on the physical layer and the data link layer, in which devices communicate with each other through media access control (MAC) addresses. It is usually used in the networking of local area networks (LANs) and data center hail knowledge (DC), and is usually implemented on switches. The switch is responsible for sending the data from the transmission to the port that matches the destination address, so as to enable communication between devices.

Layer 3 networking is a network system based on logical addresses (IP addresses), in which the network controller determines the destination and route of data to be transmitted by looking up the network prefix and host address in the logical address. This makes the communication under Layer 3 more intelligent and controllable, and is suitable for wide area network (WAN) and Internet networking. Compared with Layer 2 networking, Layer 3 networking requires more devices to implement, including routers (for transmitting IP packets) and Layer 3 switches.

In general, Layer 2 and Layer 3 networks have different applications in different scenarios. Enterprises can choose these network stacks to better serve their business needs. When implementing networking, Qi Xianchang needs to reasonably plan the network topology to achieve optimal network performance and high reliability, and meet the business requirements of the enterprise.

The main differences: Layer 2 switches work at the data link layer, Layer 3 switches work at the network layer, and routers work at the network layer.

The specific differences are as follows:

Layer 3 switches use Layer 3 switching technology.

To put it simply, the Layer 3 switching technology is: Layer 2 switching technology and Layer 3 ** technology. It solves the situation that the subnets in the network segment must rely on routers for management after the network segment is divided in the LAN, and solves the network bottleneck problem caused by the low speed and complexity of traditional routers.

What is Layer 3 Switching.

Layer 3 switching (also known as multilayer switching technology, or IP switching technology) is proposed as opposed to the traditional switching concept. As we all know, the traditional switching technology is carried out at the second layer of the OSI network standard model - the data link layer, while the three-finger blue layer switching technology realizes the high speed of data packets at the third layer in the network model. To put it simply, the Layer 3 switching technology is:

Layer 2 switching technology Layer 3 ** technology.

The emergence of Layer 3 switching technology solves the situation that the subnets in the network segment must rely on routers for management after the network segment division in the LAN, and solves the network bottleneck problem caused by the low speed and complexity of traditional routers.

The principle is as follows: Suppose two sites A and B using the IP protocol communicate through the Layer 3 switch, and the sending site A compares its IP address with the IP address of station B to determine whether station B is in the same subnet as itself when it starts to send. If destination B and sending station A are in the same subnet, Layer 2 ** is performed.

If the two sites are not in the same subnet, for example, if the sending site A wants to communicate with the destination site B, the sending site A needs to send an ARP (address resolution) packet to the default gateway, and the IP address of the default gateway is actually a Layer 3 switching module of the Layer 3 switch. When the sending station A broadcasts a large ARP request to the IP address of the default gateway, if the Layer 3 switching module already knows the MAC address of station B during the previous communication process, it replies with the MAC address of station B to the sending station A. Otherwise, the Layer 3 switching module broadcasts an ARP request to station B based on the routing information, and station B replies its MAC address to the Layer 3 switching module after receiving the ARP request, and the Layer 3 switching module saves the address and replies to the sending station A, and sends the MAC address of station B to the MAC address table of the Layer 2 switching engine.

Since then, when all packets sent from A to B are handed over to Layer 2 switching, information can be exchanged at high speed. Since Layer 3 processing is only required in the routing process, and most of the data is switched through Layer 2, the speed of Layer 3 switches is very fast, close to the speed of Layer 2 switches, and much lower than that of the same router.