Article directory
Chapter 3 Data Link Layer
3.8 Hubs and Switches
The Ethernet using the hub HUB is logically still a bus network, each station shares bus resources, and the CSMA/CD protocol (half-duplex) is used.
The hub only works at the physical layer, each of its interfaces simply forwards bits, and does not perform collision detection (checked by the network card of each station).
Hubs generally have a small amount of fault tolerance and network management capabilities.
Use hubs to extend Ethernet at the physical layer.
Switches usually have multiple interfaces. Each interface can be directly connected to a host computer or another Ethernet switch. Generally work in full-duplex mode.
The switch has parallelism and can communicate with multiple pairs of interfaces at the same time, so that multiple pairs of hosts can communicate at the same time without collision (CSMA/CD protocol is not used).
The switch works at the data link layer (including the physical layer). After receiving a frame, it searches the frame exchange table for the interface number corresponding to the destination MAC address of the frame, and then forwards the frame through the interface.
Two forwarding methods of frames:
- store and forward
- Straight-through switching: use hardware-based cross-connect matrix (switching delay is very small, but does not check whether there is an error in the frame)
the difference:
working principle: A hub is a simple physical layer device that broadcasts received data packets to all connected ports; a switch is a device that works at the data link layer, and determines the port where the data packet is transmitted to the target device based on the MAC address .
data transmission: When a device sends data, the hub will copy the data packet to all connected ports, causing network congestion and conflicts; while the switch only transmits the data packet to the port where the target device is located, realizing point-to-point communication, improving network performance and efficiency.
safety: The hub does not have any security measures, and the devices can directly access each other's data; and the switch can implement functions such as virtual local area network (VLAN), port security, etc., to enhance the security of the network.
network size: Since the hub broadcasts data to all connected devices, it is suitable for small LAN; while the switch forwards data packets according to the MAC address, it is suitable for medium and large LAN, and can support more devices to communicate at the same time.
Summarize
Hub (Hub) and switch (Switch) are two common devices in the network. They have different working methods and functions in network data transmission.
A hub is a simple device that broadcasts received data to all connected ports, regardless of the destination device. It has no store-and-forward capability of its own, nor can it identify the destination of a packet. When multiple devices send data at the same time, the hub can cause conflicts and collisions, resulting in poor network performance.
The switch is smarter and more efficient. The switch has the function of self-learning and forwarding table, which can select the correct output port according to the destination MAC address of the data packet, and only send the data packet to the port where the target device is located. In this way, data conflicts and collisions can be avoided, and the transmission efficiency and security of the network can be improved.
Switches are better suited than hubs for building large networks, providing better performance and reliability. Hubs are generally eliminated and are rarely used in modern networks.
1. The one that correctly describes the characteristics of 100Base TX is ( ).
Option
A: The transmission medium is UTP with an impedance of 100 ohms, the media access control method is CSMA/CD, the length of each cable is limited to 100m, and the data transmission rate is 100Mb/s B. The transmission medium is UTP with an impedance of 100 ohms
. The media access control method is CSMA/CD, the length of each cable is limited to 185m, and the data transmission rate is 100Mb/s
C. The transmission medium is UTP with an impedance of 100 ohms, the media access control method is Token Ring, and the cable length is limited to 185m, the data transmission rate is 100Mb/s
D The transmission medium is five types of UTP with an impedance of 100 ohms, the medium access control method is Token Ring, the cable length is limited to 100m, and the data transmission rate is 100Mb/s 2. A hub can be used to build a
LAN , You can also use switches. A group of workstations ( ) connected by a switch.
Option
A belongs to the same collision domain, but not to the same broadcast domain
B belongs to the same collision domain, but also belongs to the same broadcast domain
C does not belong to the same collision domain, but belongs to the same broadcast domain
D does not belong to the same collision domain, nor does it belong to the same broadcast domain
3 .Usually, if a computer needs to be connected to the Internet, the device that should be installed is ( ).
Option
A network operating system
B modem or network card
C network query tool
D browser
4. You can use a hub or a switch to build a LAN. A group of workstations ( ) connected by a hub.
Option
A belongs to the same collision domain, but does not belong to the same broadcast domain
B belongs to the same collision domain, but also belongs to the same broadcast domain
C does not belong to a conflict domain, but belongs to the same broadcast domain D
does not belong to a conflict domain, nor does it belong to a broadcast domain 5.
The IP of a certain host is 172 option
A 172.16. 6. If the existing l0Mb/s Ethernet is upgraded to 100Mb/s, the original connecting wire ( ). Option A can be used completely B can be used but the performance is affected C can not be used at all D can not ping the network 7. Which of the following statements is correct ( ). Option A hub can amplify the received signal B hub has information filtering function C hub has path detection function D hub has switching function 8. The hub (HUB) logically belongs to ( ) topology. Option A Mesh B Star C Bus D Ring 9. Two types of equipment are data terminal equipment (DataTerminal Equipment, DTE) and data communication equipment (Data Circuit-terminating Equipment, DCE). Option A Data communication equipment includes computers, routers, cascading ports of switches and cascading ports of hubs.
B Data terminal equipment includes ordinary ports of switches and ordinary ports of hubs.
C DTE can be distinguished from the hardware that its interface is pin type, and the interface of DCE is hole type.
D The DTE side provides the clock, and the DCE does not provide the clock, but it works on the clock provided by the DCE.
10. Which of the following is not the three major modes of Cisco IOS.
Option
A User mode
B Privileged mode
C Super mode
D Global configuration mode
11. The switch logically belongs to ( ) topology.
Option
A star
B ring
C bus
D branch
12. A traditional Ethernet LAN of 80 sites is separated into 4 collision domains. This means that at any one time there are at most ( ) stations competing for access to the medium.
Option
A 20
B 80
C 76
D 20
13. The topology in which all host nodes are connected to a central transmission line through corresponding hardware interfaces is ( ) topology.
Option
A Mesh
B Star
C Ring
D Bus
The transmission medium used by 14.1000Base-LX is ( ).
Option
A UTP
B STP
C Coaxial cable
D Optical fiber
15. In Ethernet, the cascade of hubs ( ).
Option
A must use straight-through UTP cable
B must use cross UTP cable
C must use the same speed hub
D can use different speed hubs
