Table of contents
1. The role of the data link layer
1.1 The role of data link layer
1.2 Data link layer encapsulation
2. MAC address and classification
2.2 MAC address classification
4. Working principle of switch
4.1 Working principle of switch
5. Working principle of ARP protocol
5.1 How the ARP protocol works
5.2 Working principle of ARP protocol
7.1 Advantages of Wireless LAN
7.2 Advantages of wireless LAN
Preface
This article provides an analysis of some exercises in the network skill tree, and the content is about understanding small and medium-sized LANs . The article not only gives answers to the exercises on understanding small and medium-sized LANs , but also provides specific analysis, which friends can refer to and learn. Please see the text for details.
1. The role of the data link layer
1.1 The role of data link layer
topic:
In the 7-layer structure of the OSI reference model, the frame synchronization function is implemented:
A. Data link layer
B.Physical layer
C. Transport layer
D.Network layer
Analysis: Choose A.
In the 7-layer structure of the OSI reference model, the data link layer, the second layer, implements the frame synchronization function. The data link layer is responsible for segmenting the data frame from the bit stream received by the physical layer and adding control information such as frame synchronization markers to ensure that the receiver can correctly receive, parse and process the data frame. This ensures frame-by-frame transmission and synchronization of data and reliable transmission of data. Therefore, the exact layer at which frame synchronization functionality is implemented is the data link layer.
1.2 Data link layer encapsulation
topic:
The data unit transmitted by the data link layer is ( ).
A. IP package
B. Frame
C.TCP packet
D.HTTP package
Analysis: Choose B.
Frame is the basic transmission unit in the data link layer. It contains data and control information and is used for transmission between network nodes. Frames usually include frame start and end flags, address information, verification and other fields to ensure reliable transmission and synchronization of data. The data link layer implements data reliability, error detection and correction functions by transmitting frames. Each layer has its own specific data unit, and at the data link layer, frames are the basic unit for data transmission.
1.3 Data link layer functions
topic:
Misconceptions about data links:
A. Flow control is a unique function of the data link layer
B. Frame is the transmission unit of data link layer
C. The data link layer mainly has two functions: frame coding and error correction control.
D.Ethernet protocol is a data link layer protocol
Analysis: Choose A.
Flow control is not a data link layer-specific feature. Flow control is a mechanism in network communication that is used to control the rate at which the sender sends data to the receiver to prevent the receiver from buffer overflow or network congestion. Although the data link layer can use some technologies to implement simple flow control during frame transmission, higher-layer protocols such as the TCP protocol at the transport layer also provide more complex and fine-grained flow control functions. Therefore, flow control is not a unique function of the data link layer, but a mechanism that may exist in network protocols at different levels.
1.4 Data frame format
topic:
The length range of Ethernet data frames is [
]-[] bytes.A.46-1500
B.46-1518
C.64-1518
D.64-1500
Analysis: Choose C.
The length of Ethernet data frames varies between 64-1518 bytes. Ethernet stipulates that the minimum length of a data frame is 64 bytes, which includes destination MAC address, source MAC address, type/length and other fields, as well as the data part and CRC check. The maximum length of a data frame is 1518 bytes, including the maximum supported data part and additional headers and trailers. Frame lengths outside this range are considered abnormal frames and discarded. It should be noted that this range does not include the frame's preamble and inter-frame space, which are added at the physical layer.
2. MAC address and classification
2.1 MAC address
topic:
Which of the following MAC addresses is correct:
A.00-16-5B-4A-34-2H
B.65-10-96-58-16
C.192.168.1.55
D.00-06-5B-4F-45-BA
Analysis: Choose D.
The MAC address is composed of 6 bytes, usually expressed in hexadecimal. Each byte is represented by two hexadecimal digits separated by a colon or a dash.
2.2 MAC address classification
topic:
What categories can MAC addresses be divided into:
A.Multicast, anycast
B. Broadcast, anycast
C. Unicast, multicast, broadcast
D. Unicast, broadcast
Analysis: Choose C.
MAC addresses can be divided into the following categories:
1. Unicast (Unicast): used to identify the only device in the network, one-to-one communication, the lowest bit of the first byte of the MAC address is 0.
2. Multicast: used to identify a group of devices for one-to-many communication. The lowest bit of the first byte of the MAC address is 1.
3. Broadcast: used to send data to all devices in the network. For all communications, the MAC address is all 1.
3. The role of the switch
3.1 The role of the switch
topic:
The core equipment of switched Ethernet is ().
A.Light cat
B.Router
C.Switch
D.Ap hotspot device
Analysis: Choose C.
A switch is a network device commonly used to build a local area network (LAN). It can connect multiple computers and other network devices, such as servers, printers, etc., and perform data exchange and forwarding. By learning MAC addresses and establishing forwarding tables, switches can achieve efficient transmission and forwarding of data packets and provide fast and reliable network connections. Therefore, switches are switched Ethernet core devices. Optical modems are mainly used for conversion of optical fiber access networks, routers are used to connect different networks, and AP hotspot devices are used for wireless network connections.
3.2 Function of switch
topic:
Layer 2 switches use (__) to forward data frames.
A.MAC address table
B. Routing table
C.Exchange table
D.ARP table
Analysis: Choose A.
Layer 2 switches use MAC address tables to forward data frames. When the data frame arrives at the switch, the switch looks at the destination MAC address in the data frame and matches it against the MAC address table. The MAC address table records the MAC address of the device connected to each interface. By looking for matches, the switch can determine which interface the data frame should be forwarded to achieve accurate forwarding of the data frame. Therefore, the MAC address table is the key basis for Layer 2 switches to forward data frames. Routing tables are mainly used for routing selection at the network layer. The concepts of switching tables and ARP tables are not common in Layer 2 switches and are not mechanisms used to forward data frames.
4. Working principle of switch
4.1 Working principle of switch
topic:
In the switch, a (__) table is maintained, which stores the () mapping relationship of network devices:
A.VLAN mapping relationship, VLAN and switch port
B.MAC address, MAC address and switch port
C.ARP, IP address and MAC address
D. Routing, IP address and next hop
Analysis: Choose B.
In the switch, a MAC address table is maintained, which stores the mapping relationship between the MAC address of the network device and the switch port. When a data frame arrives at the switch, the switch checks the source MAC address in the data frame and adds its corresponding port information to the MAC address table. At the same time, the switch will also check the target MAC address and find the corresponding port information in the MAC address table. By looking up the mapping relationship in the MAC address table, the switch can accurately forward the data frame to the corresponding port of the target device, realizing communication between devices in the LAN. Therefore, the MAC address table plays a key role in the switch. Among other options, VLAN mapping relationships, ARP tables, and routing tables are not common in switches and are not used to store the mapping relationship between MAC addresses and switch ports.
4.2 Switch frame processing
topic:
What happens if a frame arriving at the switch contains a destination MAC address that is not listed in the MAC address table?
A.Expired
B. Flooding
C.Learn
D.Filtering
Analysis: Choose B.
Through the flooding operation, the switch can ensure that the data frame can reach the target device and other possible receiving devices, so that the MAC address table in the network can be updated, thereby achieving normal forwarding of data. Among the other options, expiration is not a processing method. Learning and filtering are the operating behaviors of the switch, not how to handle unknown destination MAC addresses.
5. Working principle of ARP protocol
5.1 How the ARP protocol works
topic:
The main functions of the ARP protocol are:
A. Resolve hostname to IP address
B. Resolve physical address to IP address
C. Resolve IP address to physical address
D. Resolve IP address to hostname
Analysis: Choose C.
The main function of the ARP (Address Resolution Protocol) protocol is to resolve IP addresses into physical addresses. In a LAN environment, when a host needs to communicate with other hosts, it needs to know the physical address (MAC address) of the target host. The function of the ARP protocol is to query and obtain the MAC address of the target host in the LAN through broadcast. The specific process is that before sending data, the sender host will broadcast an ARP request (ARP Request) to the LAN, requesting the MAC address corresponding to the IP address of the target host. After receiving this request, the target host will respond to the sending host with its MAC address through ARP Reply. In this way, the sending host obtains the MAC address of the target host, and then can forward the data frame to the target host to realize resolution and communication from IP address to physical address. Therefore, the main function of the ARP protocol is to resolve IP addresses into physical addresses. Among other options, resolving host names into IP addresses is the function of DNS (Domain Name System). The ARP protocol does not handle the resolution of host names and IP addresses.
5.2 Working principle of ARP protocol
topic:
ARP determines the MAC address with the help of two types of data packets ( ) and ( ).
A. ARP request and ARP response
B. ARP connection and ARP response
C. ARP discovery and ARP response
D. ARP discovery and ARP connection
Analysis: Choose A.
The ARP protocol determines the MAC address of the target host by sending two types of data packets, ARP requests and receiving ARP responses. When the sender host needs to communicate with the target host, it will broadcast an ARP request (ARP Request) to request the MAC address corresponding to the IP address of the target host. After receiving this request, the target host will return its MAC address to the sending host through ARP Reply. The sending host obtains the MAC address of the target host through the received ARP response and uses the MAC address for data communication. Therefore, the MAC address resolution process of the ARP protocol involves two types of data packets: ARP request and ARP response. Among the other options, ARP connection and ARP discovery are not terms defined in the ARP protocol, so they are not correct answers.
6.VLAN
6.1 Advantages of VLAN
topic:
Which of the following is not an advantage of VLAN:
A. Simplify network management
B. Add network access nodes
C. Control network broadcast storms
D. Ensure network security
Analysis: Choose B.
VLAN (Virtual Local Area Network) is a technology that divides a physical network into logically independent virtual networks. The main advantages of VLAN include:
1. Simplify network management: VLAN can divide the network into multiple virtual networks, making network management more flexible and simplified. Administrators can independently manage and configure each VLAN as needed without configuring and managing the entire physical network.
2. Control network broadcast storms: VLAN can restrict broadcast domains and prevent broadcast storms from occurring. The broadcast signal within each VLAN will only be propagated within that VLAN and will not spread to other VLANs, thus improving network performance and stability.
3. Ensure network security: VLAN can isolate and control network traffic of different users, departments or security levels. By segregating sensitive data and users into different VLANs, you can improve network security and prevent unauthorized access and network attacks.
But option B. Increasing network access nodes is not an advantage of VLAN. On the contrary, VLAN can effectively manage and control the number of access nodes in the network by limiting broadcast domains and improving network security, thereby improving network performance and reliability. .
7.WLAN
7.1 Advantages of Wireless LAN
topic:
Which of the following is not an advantage of wireless LAN:
A. Security and Confidentiality
B. Easy to install
C. Easy to locate faults
D. Flexibility and mobility
Analysis: Choose A.
For wireless LAN, security and confidentiality are not its main advantages. Compared with wired networks, wireless LANs are more flexible and mobile, allowing users to move and access the network without a physical connection. In addition, the convenient installation of wireless LAN is also one of its advantages, as it does not require laying a large number of network cables. Security and confidentiality mainly depend on the network's security configuration and encryption method, and have less to do with the existence of a wireless LAN.
7.2 Advantages of wireless LAN
topic:
Wireless LAN uses the () method in terms of media access control (MAC).
A.PCF
B.CSMA/CA
C.Token (token) method
D.CSMA/CD
Analysis: Choose B.
CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance) is a commonly used medium access control method in wireless LAN. The reason is that in a wireless environment, signal transmission is subject to interference and attenuation, and multiple devices may try to send data at the same time, leading to collisions. Therefore, CSMA/CA adopts a collision avoidance mechanism to ensure stable and orderly data transmission on the channel.
The working principle of CSMA/CA is that before sending data, the device first monitors whether the channel is occupied by other devices. If the channel is free, the device can send data. If the channel is occupied, the device needs to wait for a random period of time before retrying to avoid collisions caused by sending data at the same time. In addition, CSMA/CA also uses the ACK (acknowledgment response) mechanism. The sender will wait for the confirmation signal sent by the receiver to ensure the correct transmission of data.
Compared with the CSMA/CD (Carrier Sense Multiple Access with Collision Detection) method, CSMA/CA is more suitable for wireless network environments, because in wireless networks, collisions cannot be accurately detected due to the characteristics of signal transmission. CSMA/CA can improve the transmission efficiency and reliability of wireless networks by avoiding collisions.
8. PPP Agreement
8.1 PPP Agreement
topic:
PPP is a ( ) protocol.
A.Physical layer
B.Application layer
C. Network layer
D. Data link layer
Analysis: Choose D.
PPP (Point-to-Point Protocol) is a protocol used in the data link layer. It is designed for data transmission between two network nodes directly connected via a serial line.
The main function of PPP is to provide reliable point-to-point connections and support the encapsulation and transmission of multiple network protocols. It can work on different physical media such as serial lines, fiber optics, coaxial cables, etc. The PPP protocol defines the format of data frames, frame assembly and parsing, error detection and correction and other functions to achieve reliable data transmission.
Since PPP works at the data link layer, it can adapt to various network layer protocols, such as IP, IPX, etc., and encapsulate network layer protocol data in PPP frames for transmission. Therefore, PPP can be regarded as a protocol that provides transmission of multiple network layer protocols on the data link layer.
Summarize
This article only provides answers and analysis to the exercises in the understanding of small and medium-sized LANs in the network skill tree. The content of this article is simple. For detailed information and more knowledge points, please check the reference materials in the network skill tree.
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