2. How to implement 2.DNS?
3. Load balancing of 3.WEB server?
4. What are the advantages and disadvantages of several common network operating systems on the market?
5. Which servers have you used? Please describe the characteristics and advantages of raid0 0, 1, 5?
6. Please list the segmentation slogans of the following protocols: http, https, DNS, FTP, telnet, PPTP, SMTP, POP3?
7. If you want to access the other computer through the UNC path or NETBIOS name in the LAN, what protocol or port do you need to open on the other computer?
8.OSI seven-layer model? TCP/IP model?
9. can 9.WIN2000P be upgraded to WIN2000S?
10. How to ensure the security of 1 document?
1 1. What do you know about firewalls and their applications?
12, how to realize WINDOWS domain? What should customers do to join a domain?
13, are you familiar with AD? How to organize advertising resources?
14. Please briefly describe the function of FSMO.
15. What is PKI? How to realize PKI under WIN? Please briefly describe the process of applying for a certificate?
16, have you used those remote control software?
17, how to realize WINDOWS cluster?
18. What kind of mail system do you know? Please briefly describe the detailed steps of installing EXCHANG 2003?
19. What are the functions of isa? Please briefly describe the process of publishing a website with ISA?
20. How to make SQL server more secure?
2 1. How should you plan the storage of SQL database files in the production environment?
22. What should you do when DC falls?
23. How to make your WINDOWS server more secure?
24. How to back up and restore the SQL database?
25. How to back up and restore the EXCHANG database?
26. What antivirus software have you used (online version and stand-alone version)?
27. If there is a small business network that you need to plan, please tell us your planning ideas?
28. Do you know those intrusion detection systems? What can be deployed independently?
29. How to strengthen the security of WEB server?
30. When the computer breaks down, how do you solve this problem?
3 1, is there any system patch upgrade? If there are 100 machines in the intranet, how to upgrade the system patch?
32. Is there any confusion on the webpage? What is the reason?
33. After the successful installation of Exchange 2003, can I use foxmail to send and receive emails by default? If so, why? If not, please explain why?
34. How to uniformly change the email address of the whole company (exchange environment)?
35. How do you plan the storage of EXCHANGE server database in production environment?
36. Please write down the measures above 10 to ensure the network security of your enterprise.
37.WINDOWS XP clients need ten minutes to log in to the domain. What is the reason? How to solve it?
38. When users report that accessing the file server is very slow, what are the reasons? How to solve it?
39. When users report that Internet access is slow, what are the reasons? How to solve it?
This article comes from the technical blog of 5 1CTO. Computer output microfilm
The definition of a computer network, talk about your understanding of the network.
A system that connects many computers with independent functions distributed in different places through communication equipment and lines, and realizes resource sharing in the network under the operation of fully functional network software. (understand)
Please describe the osi seven-layer model and briefly summarize the functions of each layer.
OSI stands for Open Systems Interconnection. The model divides the work of network communication into seven layers, from low to high, namely physical layer, data link layer, network layer and transport layer. Session layer, presentation layer and application layer. The first layer to the third layer belong to the lower three layers of the OSI reference model and are responsible for creating the link of network communication connection; The fourth to seventh layers are the upper four layers of the OSI reference model, which are responsible for end-to-end data communication. Each layer performs certain functions, each layer directly provides services to its upper layer, and each layer supports each other, while network communication can be carried out from top to bottom (at the sender) or from bottom to top (at the receiver). Of course, not every communication needs to go through all seven layers of OSI, and some even need only one layer to correspond to both parties. The transmission between physical interfaces and the connection between repeaters only need to be carried out at the physical layer; The connection between routers only needs to go through three layers below the network layer. Generally speaking, the communication between the two sides is carried out on the level of reciprocity, not on the level of asymmetry.
The division of each layer of OSI reference model follows the following principles:
1. Each network node in the same layer has the same hierarchical structure and the same function.
2. Adjacent layers in the same node communicate through interfaces (which can be logical interfaces).
3. Each layer in the seven-layer structure uses the services provided by the lower layer and provides services to the upper layer.
4. Peer layers of different nodes communicate with each other according to the protocol.
The first layer: the physical layer.
Specify the mechanical, electrical, functional and process characteristics of communication equipment for establishing, maintaining and dismantling physical links. Specifically, the mechanical characteristics specify the specifications, dimensions, number of pins and arrangement of connectors required for network connection. When the bit stream is transmitted over the physical connection, the electrical characteristics specify the signal level, impedance matching, transmission rate distance limit and so on. Functional characteristics refer to giving each signal an exact signal meaning, that is, defining the function of each line between DTE and DCE; The characteristics of rules define a set of operation rules for bit stream transmission through signal lines, which refers to the action sequence of establishing, maintaining and exchanging information in physical connection, that is, placing DTE and DCE on each circuit.
At this level, the unit of data is called bit.
Typical specifications that belong to the definition of physical layer are: EIA/TIA RS-232, EIA/TIA RS-449, V.35, RJ-45, etc.
Layer 2: Data link layer.
Based on the bit stream service provided by the physical layer, the data link between adjacent nodes is established, the error-free transmission of data frames on the channel is provided through error control, and a series of actions are carried out on each circuit.
The data link layer provides reliable transmission through unreliable physical media. The functions of this layer include: physical address addressing, data framing, flow control, data error detection and retransmission.
At this layer, the unit of data is called a frame.
Representatives of data link layer protocols are: SDLC, HDLC, PPP, STP, Frame Relay, etc.
Layer 3: Network layer.
There may be many data links and many communication subnets between two computers communicating in a computer network. The task of the network layer is to select the appropriate routing and switching nodes between networks to ensure the timely transmission of data. The network layer assembles the frames provided by the data link layer into data packets, and the data packets are encapsulated by network layer headers, which contain logical address information-network addresses of source site addresses and destination site addresses.
If you're talking about an IP address, then you're dealing with a Layer 3 problem, a "packet" problem, not a Layer 2 "frame". IP is a part of the Layer 3 problem, and there are some routing protocols and address resolution protocols (ARP). Everything about routing is handled at Layer 3. Address resolution and routing are important purposes of Layer 3. The network layer can also realize congestion control, Internet interconnection and other functions.
At this layer, the unit of data is called a packet.
The representatives of network layer protocols are: IP, IPX, RIP, OSPF, etc.
The fourth layer: the transport layer that processes information.
Layer 4 data units are also called data packets. However, when you talk about specific protocols such as TCP, you have a special name. The data unit of TCP is called segment, and the data unit of UDP is called datagram. This layer is responsible for obtaining all information, so it must track data unit fragments, packets that arrive out of order and other dangers that may occur during transmission. Layer 4 provides transparent and reliable end-to-end (end-user-to-end) data transmission services for the upper layer. Transparent transmission means that the transport layer shields the upper layer from the specific details of the communication transmission system during the communication process.
Representatives of transport layer protocols are: TCP, UDP, SPX, etc.
The fifth layer: the conversation layer.
This layer can also be called conference layer or dialogue layer. At the higher level above the session layer, the unit of data transmission is no longer named separately, and is collectively called message. Session layer does not participate in specific transmission, but provides a mechanism to establish and maintain communication between applications, including access verification and session management. If the server verifies the user login, it is done by the session layer.
The sixth layer: presentation layer.
This layer mainly solves the problem of grammatical representation of publicity information. It transforms the data to be exchanged from an abstract syntax suitable for users to a transmission syntax suitable for use in OSI systems. In other words, it provides formatted presentation and transformation data services. The presentation layer is responsible for data compression and decompression, encryption and decryption.
The seventh layer: the application layer.
The application layer provides an interface for the operating system or network applications to access network services.
The representatives of application layer protocols are: Telnet, FTP, HTTP, SNMP, etc.
Please describe the tcp/ip model and briefly introduce the functions of each layer.
For various reasons, OSI model has not become a real network architecture applied in industrial technology. In the early days of network development, the geographical coverage of the network was very limited, and its main purpose was only to serve the US Department of Defense and military scientific research institutions. With the development of civil use, the network is connected to universities and other units through telephone lines, and it is further necessary to expand the network through satellites and microwave networks. The original technical standards of military network can no longer meet the needs of increasingly civilian use and network interconnection, so it is put on the agenda to design a set of technical standards to realize seamless interconnection between various networks. This network architecture is the later TCP/IP reference model.
TCP/IP model is divided into four layers, namely, application layer, transport layer, Internet layer and host to network layer. Each layer realizes specific functions, provides specific services and access interfaces, and is relatively independent.
(1) Host to Network Layer
Host to network layer is the first layer of TCP/IP model. It is equivalent to the physical layer and data link layer in the OSI model, because its function is to send data from the host to the network. Similar to the application of postal system, the bit stream transmission from the host to the network layer is equivalent to the delivery of letters.
(2) Internet layer
Internet layer is the second layer of TCP/IP model. At first, people hoped that when some devices in the network could not operate normally, the network service would not be interrupted, and the established network connection could still transmit data effectively. In other words, as long as the source host and the destination host are in normal state, the network is required to complete the transmission task. It is under these harsh design goals that the Internet layer chooses packet switching technology as the solution.
Packet switching technology not only enables the packets to roam to the target host independently after being sent to any network, but also ensures that the packets received by the target host are out of order and send them to the highest layer to rearrange the packet order. The Internet layer defines the standard packet format and interface parameters. As long as these standards are met, data packets can roam between different networks.
(3) Transport layer
The transport layer is the third layer in the TCP/IP model. Its function is similar to the transport layer in OSI model. The transport layer in TCP/IP model can not only provide transmission services with different service levels and different reliability guarantees, but also coordinate the transmission speed difference between the sender and the receiver.
(4) Application layer
The application layer is the fourth layer in the TCP/IP model. Different from OSI model, TCP/IP model has no session layer and presentation layer. Because it is found in the application that not all network services need the functions of session layer and presentation layer, these functions are gradually integrated into those specific network services of application layer in TCP/IP model. The application layer is the application interface of network operators. Just like the sender puts a letter in the mailbox, the network operator only needs to press the send data button in the application, and the rest of the tasks are completed by the layers below the application layer.
Please briefly describe the difference between a switch and a hub.
The simplest difference is that the hub is broadcast and users enjoy bandwidth; Switches are interactive and each user has its own bandwidth.
In today's global networked network era, the network has become a necessity of human life. Switches and hubs are important devices for establishing local area networks, and they both play the role of "hubs" for data transmission in local area networks. So, what is the difference between a switch and a hub?
The so-called switch is actually developed from hub technology. If you describe the difference between a switch and a hub in the simplest language, it should be the difference between intelligent and non-intelligent. To put it bluntly, a hub is a device that connects multiple computers. It can only play the role of signal amplification and transmission, but it can't deal with the fragments in the signal, so it is very easy to make mistakes in the transmission process. The switch can be regarded as an intelligent hub, which not only includes all the functions of the hub, but also has the functions of automatic addressing, switching and processing. And in the transmission process, only the sending source and the receiving source work independently, which has nothing to do with other ports, thus achieving the purpose of preventing data loss and improving throughput.
Next, I will analyze and explain the differences between switches and hubs from their concepts, types, characteristics, OSI architecture, working methods and other basic issues.
1. The concept of switches and hubs
The English name of 1. 1.Switch is "switch", which is an upgraded product of hub. From the appearance, it is basically not much different from hub. It is a rectangular box with multiple ports. According to the needs of information transmission at both ends of communication, the switch sends the information to be transmitted to the corresponding qualified route through manual or automatic equipment. Generalized switch is a kind of equipment that completes information exchange function in communication system.
1.2. Hub A hub is a connecting device that connects multiple computers or other devices in a computer network, and it is the smallest unit of centralized network management. English HUB means center. Like a trunk, it is the intersection of all branches. Many types of networks rely on hubs to connect various devices and distribute data to various network segments. HUB is basically a * * * shared device, and its essence is a repeater, which mainly provides the functions of signal amplification and transit, and distributes all signals received by one port to all ports.
2. Types of switches and hubs
Switches and hubs have different classifications from different aspects and angles.
2. 1. Hub type
There are many types of hubs, each of which has a specific function and provides different levels of services.
2. 1. 1. According to different bus bandwidths, hubs can be divided into three types: 10M, 100M and10m. According to different configuration forms, it can be divided into independent, modular and stacked types.
2. 1.2. According to the number of ports, there are mainly 8 ports, 16 ports and 24 ports.
2. 1.3. According to the working mode, it can be divided into intelligent and non-intelligent. The hubs currently used are basically the combination of the first three categories, such as 10M/ 100M adaptive intelligent stackable hub that we often see in advertisements.
2. 1.4. It is of universal significance to distinguish the working modes, which can be further divided into four types: passive hub, active hub, intelligent hub and switching hub.
2.2. Classification of switches
2.2. 1. According to the complex network structure, network switches are divided into access layer switches, convergence layer switches and core layer switches. Among them, the core layer switches are modular in chassis design. At present, the 1000BASE-T module has been basically designed, and the selection of core layer switches is not discussed in this paper. The Ethernet switch supporting 1000BASE-T in the access layer is basically a fixed port switch, with101000 Mbps as the main port, and the uplink port of 1000BASE-T is provided in the form of a fixed port or expansion slot. Convergence layer 1000BASE-T switch has two designs at the same time, namely chassis type and fixed port type, which can provide multiple 1000BASE-T ports and other ports such as 1000base-X generally. The access layer and convergence layer switch * * * together form a complete small and medium-sized LAN solution.
2.2.2. According to the OSI 7-layer network model, switches can be divided into Layer 2 switches, Layer 3 switches, Layer 4 switches and so on, all the way to Layer 7 switches. Layer 2 switches based on MAC addresses are the most common, which are used in the network access layer and convergence layer. Layer 3 switches based on IP address and protocol are widely used in the core layer of the network, and a few are used in convergence layer. Some three-layer switches also have a four-layer switching function, which can judge the target port according to the protocol port information of the data frame. Switches above the fourth layer are called content switches, which are mainly used in Internet data centers and are beyond the scope of this paper.
2.2.3. According to the manageability of switches, they can be divided into manageable switches and unmanageable switches. Their difference lies in their support for network management protocols such as SNMP and RMON. Manageable switches are convenient for network monitoring, but the cost is relatively high. Convergence layer's large and medium-sized networks should choose manageable switches. In the access layer, all switches in the core layer are managed switches depending on the application requirements.
3. Functions of switches and hubs
3. Characteristics of1. centre
In the star structure, it is the intermediate node of the connection and plays the role of amplifying the signal. All devices * * * enjoy the bandwidth of the hub, that is, if the bandwidth of the hub is 10M and 10 devices are connected, then each device is 1M, and all ports of the hub * * * enjoy a MAC address.
3.2. Features of the switch
When used in the star structure, as the central node to amplify the signal, the port does not enjoy the bandwidth. If it is a 10M switch, then the bandwidth of each port is 10M, and each port has its own MAC address.
The main functions of the switch include physical addressing, network topology, error checking, frame sequence and flow control. At present, some high-end switches have some new functions, such as supporting VLAN (Virtual Local Area Network), supporting link aggregation, and some even have the functions of routing and firewall.
Switches can not only connect the same type of networks, but also interconnect different types of networks (such as Ethernet and Fast Ethernet). Nowadays, many switches can provide high-speed connection ports supporting fast Ethernet or FDDI, which can be used to connect other switches in the network or provide extra bandwidth for key servers with large bandwidth occupation.
It is a network device with some functions of a router. It can decide where to send the received data, which is faster than the router.
4. The main differences between switches and hubs
From the above analysis, we can know that the main differences between switches and hubs are divided into four aspects, namely OSI architecture, data transmission mode, bandwidth occupation mode and transmission mode.
4. The difference between1.OSI architecture The hub belongs to the first layer physical layer equipment of OSI, while the switch belongs to the second layer data link layer equipment of OSI. In other words, the hub only plays the role of synchronization, amplification and shaping in data transmission, and cannot effectively deal with short frames and fragments in data transmission, and cannot guarantee the integrity and correctness of data transmission; The switch can not only synchronize, amplify and shape data transmission, but also filter short frames and fragments.
4.2. Differences in data transmission modes
At present, 80% LAN is Ethernet, and hubs or switches are widely used in LAN. LAN connected by hubs is called shared LAN, and LAN connected by switches is called switched LAN.
4.2. 1. Different working methods. Let's talk about the two concepts of * * * sharing and communication in the network. Here, let's make an analogy. It is also a road with 10 lane. If the driving route is not clearly marked for the road, then vehicles can only grab or occupy the road in a disorderly state, which is prone to traffic jams and collisions between opposite vehicles, reducing the capacity. In order to avoid the above situation, it is necessary to clearly mark the lanes on the road to ensure that each car goes its own way and does not interfere with each other. * * * addiction network is equivalent to the disorder mentioned above. When the number of data and users exceeds a certain limit, it will cause collision and degrade the network performance. Switched networks avoid the shortcomings of * * * shared networks. The function of switching technology is to send each packet from one port to the destination port independently according to the destination address of the transmission packet, which avoids the collision with other ports and improves the real-time throughput of the network.
* * * The main problem of enjoyable Ethernet is that all users * * * enjoy bandwidth, and the actual available bandwidth of each user decreases with the increase of network users. This is because when the information is busy, there may be multiple users "competing" for a channel at the same time, and a channel is only allowed to be occupied by one user at a certain moment, so a large number of users are often in the state of listening and waiting, which leads to jitter, stagnation or distortion in signal transmission and seriously affects network performance.
In switched Ethernet, the switch provides a dedicated information channel for each user. Unless two source ports try to send information to the same destination port at the same time, each source port and its respective destination port can communicate at the same time without collision.
4.2.2. Different working mechanisms The working mechanism of the hub is broadcasting. No matter what type of data packets are received from which port, they will be sent to all other ports in the form of broadcast. The network card (NIC) connected to these ports will judge and process the information, and those that meet the requirements will be left for processing, otherwise they will be discarded, which will easily lead to a broadcast storm, and the network performance will be greatly affected when the network is large. From its working state, the hub is inefficient (sending packets to all ports) and has poor security (all network cards can receive, but non-destination network cards will discard packets). Moreover, only one packet can be processed at a time, and multiple ports have packets at the same time, which will conflict. Packets are processed serially, which is not suitable for large network backbones.
The switch works completely differently. It analyzes the header information of Ethernet packets (including original MAC address, target MAC address, information length, etc. ), get the target MAC address, look up the address comparison table (the port corresponding to the MAC address) stored in the switch, confirm which port the network card with the MAC address is connected to, and then only send the data packet to the corresponding port, which effectively suppresses the broadcast storm.
This is the biggest difference between a switch and a hub. The bandwidth of the backboard for forwarding messages inside the switch is also much larger than the bandwidth of the port, so the messages are in a parallel state with high efficiency, which can meet the requirements of large-scale network environment for parallel processing of a large number of data.
4.3. Differences in Bandwidth Occupancy Patterns
No matter how many ports there are in the hub, all ports share a bandwidth, only two ports can transmit data at the same time, other ports can only wait, and the hub can only work in half-duplex mode; For switches, each port has its own bandwidth, and in terms of speed, each port has a fundamental guarantee. When two ports work, the work of other ports is not affected, and the switch can work in either half-duplex mode or full-duplex mode.
4.4. Differences in communication modes
The hub can only transmit in half-duplex mode, because the hub enjoys the transmission medium, so the hub can only transmit one task at a time on the uplink channel, either receiving data or sending data. On the other hand, the switch uses full-duplex mode to transmit data, so it can receive and send data at the same time, which not only greatly speeds up the data transmission, but also is at least twice as fast as the hub in terms of the throughput of the whole system, because it can receive and send data at the same time, which is actually far more than twice, because the port bandwidth of the switch is generally many times wider than the hub.
For a simple example, let two groups of people transfer a file to each other at the same time, and the time from one person to the other is 1 minute. If a hub is used, it will take 4 minutes. Data is first transmitted from one person to another, and then the other person returns. Then the other group can do the same job, which is 4 minutes. But with the switch, the speed is much faster. In the same case, it only takes 1 minute. Because each port is independent, these two groups of people can transmit data at the same time, and because the switch can work at full duplex, every two people can also transmit at the same time, in other words, these four people can finish their work at the same time. Therefore, we can also regard the processing capabilities of hubs and switches as serial processing and parallel processing.
summary
To sum up, the function of the hub is just a multi-port repeater. No matter which port the signal comes from, it will be broadcast to all ports after shaping, regeneration and amplification. All ports use the same bandwidth of * * * frequency band, which will greatly reduce the bandwidth of all ports in the case of large data volume. The switch is equivalent to a multi-port bridge, providing users with a dedicated point-to-point connection. Data packets are only sent to the destination port, not to all ports, which reduces the collision of signals in the network, and all ports on the switch have exclusive channel bandwidth.
Switch is a new type of network connection equipment developed on the basis of hub, which has better and more powerful functions and advantages, high cost performance and is more suitable for the needs of today's network. From the above analysis, we can easily see the obvious advantages of switches over hubs. I believe that in the near future, switches will completely replace hubs.
This article comes from the technical blog of 5 1CTO. Computer output microfilm