Conflict Domain broadcast Domain

Source: Internet
Author: User

First, the concept of understanding:

1. Conflict domain (physical segmentation):

A collection of all workstations connected on the same wire, or a collection of all nodes on the same physical network segment, or a collection of nodes competing for the same bandwidth on the Ethernet. This field represents the area in which the conflict occurs and propagates, and this area can be considered a shared segment. In the OSI model, conflict domains are considered the first layer of concepts, and devices that connect to the same conflict domain have hub,reperter or other devices that perform simple replication signals. That is, all nodes connected with the hub or repeater can be considered to be within the same conflict domain, and it will not divide the conflict domain. The second layer of equipment (bridge, switch) third-tier devices (routers) can be divided into conflict domains, of course, can also be connected to different conflict domains. Simply put, the repeater can be regarded as a cable, and the bridge as a bundle of cables.

2. Broadcast domain:

A collection of nodes that receive the same broadcast message. For example, if one of the nodes in the collection transmits a broadcast frame, all other nodes that can receive the frame are considered part of the broadcast frame. Because many devices are extremely easy to produce broadcasts, if not maintained, it consumes a lot of bandwidth and reduces the efficiency of the network. Since the broadcast domain is considered to be the second-level concept in the OSI, the nodes connected to the second-tier device are considered to be in the same broadcast domain, such as hub, switch, and so on. Routers, the third layer of switches can be divided into broadcast domain, that is, can be connected to different broadcast domains.

Second, the conflict domain and the broadcast domain in the network interconnection equipment characteristic:

The common network interconnection devices work and their respective characteristics when dividing the conflict domain and broadcast domain. Reference point:[email protected]/blog/static/62569847200822442030457/

1. Traditional Ethernet operation

The typical representative of traditional shared Ethernet is the total linear Ethernet. In this type of Ethernet, there is only one communication channel, using media sharing (media contention) access method (The 1th chapter describes the CSMA/CD media access method). Each site will first listen to the network if it is idle before sending the data, and if it is idle, send the data. Otherwise, continue listening until the network is idle. If two sites simultaneously detects that the media is idle and sends out a frame of data at the same time, it will cause a conflict of data frames, and both sides of the data frames are destroyed. At this point, two sites will use the "binary exponential Backoff" method to wait for a random time to listen and send.


In Figure 1, host a simply 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 to send data to the bus will conflict, resulting in both data sending failed. We say that all the hosts connected on the bus form a conflict domain.


When host A sends a broadcast-type packet that targets all hosts, all hosts on the bus receive the broadcast packet and examine the contents of the broadcast packet, further processing if necessary. We call all the hosts connected on the bus together to form a broadcast domain.

Figure 1 Traditional Ethernet

2. Repeater (Repeater)

Repeaters (Repeater) appear as a real product for two main reasons:

First, extend the network distance and regenerate the attenuation signal.

Second, the interconnection of coarse coaxial cable Ethernet and fine coaxial cable Ethernet is realized.

Although the repeater can prolong the distance of the signal transmission and realize the interconnection of the two network segments. But it does not increase the bandwidth available to the network. As shown in 2, the network Segment 1 and the network Segment 2 are connected by a repeater to form a single conflict domain and broadcast domain.

Figure 2 Network of repeater connections

3. Hub (Hub)

Hubs actually correspond to multi-port repeaters. A hub typically has 8, 16, or 24 equal numbers of interfaces.

Hubs can also extend network communication distances, or connect to networks with different physical structures, but primarily as a aggregation point for a host site, connecting hosts connected to each interface on the hub so that they can communicate with each other.

As shown in 3, all hosts are connected to hubs on the hub to form a physical star connection. But in fact, inside the hub, each interface is connected by a Backplane bus, which still logically forms a shared bus. As a result, the hub and the hosts that are connected to all of its interfaces form a conflict domain and a broadcast domain.

Figure 3 Network connected to a hub

4, Bridges (bridge)

Bridges are also known as bridge connectors. Similar to repeaters, a traditional bridge has only two ports for connecting different network segments. And the repeater is different, the bridge has a certain "intelligence", can "learn" the address of the host network, and also has the function of signal filtering.


As shown in 4, packet 1 of host A to host B packets will not be forwarded to the network Segment 2. Because, the bridge can recognize that this is a network segment 1 internal communication data flow. Similarly, the network Segment 2 of the host X to host y packets will not be forwarded to the network Segment 1. It can be seen that the bridge divides a conflict domain into two. Where each conflict domain shares its own bus channel bandwidth.

Figure 4 Network for a bridge connection

However, if host C sends a destination that is a broadcast type packet for all hosts, the bridge is going to forward such a packet. All hosts on each of the two network segment buses on both sides of the bridge are receiving the broadcast packet. Therefore, network Segment 1 and Segment 2 still belong to the same broadcast domain.

5. Switching (switch)

The switch is also known as a switched hub. It appears to resolve the flaw in sharing available bandwidth for all hosts connected to the hub.

The switch is to increase the available bandwidth by directly establishing a dedicated communication channel for the two hosts that need to communicate. From this point of view, the switch corresponds to a multi-port bridge.

As shown in 5, the switch establishes a dedicated channel for host A and Host B, and a dedicated channel for host C and host D. Only when an interface is connected directly to a hub and the hub is connected to more than one host, the interface on the switch and all hosts connected on the hub are likely to conflict and form a conflict domain. In other words, each interface on the switch is a conflict domain of its own.

Figure 5 Network connected to the switch

However, the switch also does not have the ability to filter broadcast traffic. If a switch receives a broadcast packet, it forwards the broadcast packet to all its ports. As a result, the switch and the hosts to which all its interfaces are connected form a broadcast domain.

We will use the switch as the interconnection device of the local area network called the switched LAN.

6. Router (Router)

The router works at the network layer, can identify the network layer address-IP address, has the ability to filter the 3rd layer of broadcast messages. In fact, a router never forwards a broadcast-type packet unless a special configuration is made. As a result, the network to which each port of the router is attached constitutes a broadcast domain on its own. 6, if each network segment is a shared LAN, each network segment itself constitutes a separate conflict domain.

Figure 6 router-connected network

7. Gateways (Gateway)

The gateway works at the senior level of the OSI Reference Model, and therefore does not use the concept of a conflict domain or broadcast domain. Gateways are primarily used to convert between high-level protocols. For example, act as a mail gateway between the Lotus 1-2-3 mail service and the Microsoft Exchange Messaging Service.

Note that the concept of the gateway here is completely different from the PC host and the default gateway configured on the router.

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Conflict Domain broadcast Domain

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