Illustration: "broadcast domain, conflict domain", "various devices", "shared LAN vs. Switched LAN"

Source: Internet
Author: User

Network interconnection devices can divide networks into different conflicting and broadcast domains. However, different network interconnection devices may work at different layers of the OSI model. Therefore, the effect of dividing conflicting domains and broadcast domains is also different. For example, a repeater works on the physical layer, a bridge and a switch work on the data link layer, a router works on the network layer, and a gateway works on the top three layers of the OSI model. Network interconnection devices at each layer need to complete different tasks according to the characteristics of different layers.
Next we will discuss the working principles of common network interconnection devices and their respective characteristics when dividing conflicting domains and broadcast domains. 1. A typical example of a traditional Ethernet shared-bandwidth network is bus-type Ethernet. In this type of Ethernet, there is only one communication channel, using a media sharing (Media contention) access method. Before sending data, each site must first check whether the network is idle and send data if it is idle. Otherwise, continue listening until the network is idle. If the two sites detect that the media is idle and one frame of data is sent at the same time, the data frame conflicts and the data frames of both sites are damaged. At this time, the two sites will use the "Binary Index backoff" method to wait for a random period of time before listening and sending. In Figure 1, host A only wants to send A unicast packet to host B. However, due to the broadcast nature of the traditional shared Ethernet, all hosts connected to the bus will receive this unicast packet. At the same time, if any second party, including host B, also needs to send data to the bus, it will conflict, causing both parties to send data to fail. We call all hosts connected to the bus constitute A conflict domain (Sam: All Hosts that A receives even if it sends unicast packets ). When host A sends A broadcast data packet destined for all hosts, all hosts on the bus must receive the broadcast data packet and check the content of the broadcast data packet, further processing is required. We call all hosts connected to the bus constitute A broadcast domain (Sam: all hosts that can receive broadcast packets sent by ).

Figure 1. Traditional Ethernet 2 and Repeater appear as a product mainly for two reasons: 1. Expand the network distance and regenerate the attenuation signal. Second, Ethernet Interconnection between coarse and fine coaxial cables is realized. Although the repeater can extend the signal transmission distance and achieve the interconnection of the two network segments. However, no available bandwidth is added. As shown in figure 2, CIDR Block 1 and CIDR Block 2 form a single conflict domain and broadcast domain after being connected by a repeater. (Sam: a repeater is equivalent to a common transmission medium)

Figure 2. network connected by relay 3. a hub is actually a repeater with multiple ports (in this chapter, we often use the word "Port" to replace the term "interface. A hub usually has eight, 16, or 24 interfaces. A hub can also extend the communication distance between networks or connect networks with different physical structures, but it is mainly used as a collection point for a host site, connect hosts connected to interfaces on the hub so that they can communicate with each other. As shown in 3, all hosts are connected to the hub of the central node to form a physical star connection. But in fact, in the hub, each interface is connected through the backplane bus and logically forms a shared bus. Therefore, the hub and the hosts connected to all its interfaces form a conflict domain and a broadcast domain.

Figure 3 network connected by a hub 4. A Bridge is also called a Bridge. Similar to a repeater, a traditional bridge has only two ports used to connect different network segments. Different from the repeater, the bridge has a certain "smart" nature, can "Learn" the address of the host on the network, and has the function of signal filtering. As shown in 4, packets sent from host A of Network Segment 1 to host B are not forwarded by the bridge to Network Segment 2. Because the bridge can recognize that this is the communication data flow within segment 1. Similarly, data packets sent from host X of CIDR Block 2 to host Y are not forwarded to CIDR Block 1 by the bridge. It can be seen that the bridge can divide a conflict domain into two. Each conflicting domain shares its own bus channel bandwidth. However, if host C sends a broadcast data packet destined for all hosts, the bridge will forward the packet. All hosts on the two CIDR blocks on both sides of the bridge must receive the broadcast packet. Therefore, CIDR Block 1 and CIDR Block 2 still belong to the same broadcast domain.

Figure 4. network connected by a bridge 5. A Switch is also called a Switch. It is used to solve the defect of sharing available bandwidth among all hosts connected to the hub. Vswitches increase the available bandwidth by directly establishing a dedicated communication channel for the two hosts to communicate. From this perspective, the switch is equivalent to a multi-port bridge. As shown in 5, the switch establishes A dedicated channel for host A and host B, and also creates A dedicated channel for host C and host D. Only when an interface is directly connected to a hub and the hub is connected to multiple hosts can this interface conflict with all hosts connected to the hub, form a conflict domain. In other words, each interface on a vswitch is a conflict domain of its own. However, vswitches do not have the function of filtering broadcast communication. If the switch receives a broadcast packet, it forwards it to all its ports. Therefore, the vswitch and the host connected to all its interfaces form a broadcast domain. We will use a vswitch as the LAN for connecting devices.

Figure 5. vswitch-connected network 6. the Router (Router) works at the network layer. It can identify the IP address at the network layer and can filter broadcast messages at Layer 3rd. In fact, the router never forwards broadcast data packets unless otherwise configured. Therefore, the network connected to each port of the router is a broadcast domain. As shown in figure 6, if each CIDR Block is a shared LAN, each CIDR block forms an independent conflict domain.

Figure 6. vro7 connected network 7. The Gateway works on the layer 3 of the OSI reference model. Therefore, the concept of conflict domain and broadcast domain is not used. Gateways are mainly used to convert between high-level protocols. For example, act as the mail gateway between the LOTUS 1-2-3 mail service and the Microsoft Exchange mail service. Note that the concept of gateway here is completely different from that of the default gateway configured on the PC host and vro ). This article is from the China IT lab

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