1. Write in front
In fact, when doing simulations or real questions, you will always lose points in key areas, so I calmed down and thought about it. First, we sorted out the knowledge involved in the questions we have done, and secondly, we will do some questions based on the knowledge. I only got 38 points in the test this time, and I was very sad. There are less than 10 days to supplement my knowledge. Come on! ! !
`Copyright statement: This article was originally written by the CSDN blogger - "Learning Soft Codes for the Blind with a Cane". There are many shared codes on the homepage. We look forward to your visit. `
2. Wrong question set
1. The CPU responds to the DMA request at the end ofa bus cycle;
[Extension] The resource occupied by the DMA operation is the system bus, and the CPU does not use the bus during the entire instruction execution period, that is, within the instruction cycle. Therefore, the detection point of the DMA request is set to be executed at the end of each machine cycle, that is, the bus cycle, so that Bus utilization is the highest.
2. The virtual storage system is composed ofmain memory and auxiliary memory;
[Extension] There are two main storage systems in general computer systems
Cache storage system: It consists of Cache and main memory. Its main purpose is to increase the memory speed and is transparent to system programmers and above;
Virtual storage system: It consists of main memory and auxiliary storage such as online disk storage. The main purpose is to expand the memory capacity and is transparent to application programmers.
3. In the address field of the machine instruction, the addressing mode that directly points out the operand itself is called immediate addressing
[Extended] Common addressing methods
Immediate addressing: Directly point tothe operand itself. The fastest way to get operands
Direct addressing: The part of the instruction after the opcode field isthe address of the operand.
Indirect addressing: The address given in the instruction isthe address of the operand address.
Register addressing:The specified register stores theoperand itself< a i=4>.
Register indirect addressing:The specified register stores the address of the operand.
4. The difference between a hub and a bridge is thatA hub is a physical layer device, while a bridge is a data link layer device
【extend】
Hub: It is a collection of coaxial cables in a box. This box only has the function of receiving and sending. It can detect sending conflicts, but it cannot identify frames at the data link layer.
Bridge: It is a data link layer device. It can identify the data link layer MAC address and selectively send frames to the output port. The bridge can also have multiple ports. If there are many bridge ports and accelerated forwarding is configured The hardware becomes a LAN switch.
5. According to the STP protocol, the bridge ID consists of 2 bytes and the bridge priority of It is composed of 6-byte bridgeMACaddress, with a value range of It is 0~65535 (0 to 2^16-1), and the default value is 32768 (2 to the 15th power).
6. Regarding the ICMP protocol, the following statement is correct: ICMP can transmit error information that occurs during IP communication
[Extension] ICMP and IP are both network layer protocols and are used to transmit messages about communication problems, such as datagrams that cannot reach the destination, the router does not have enough cache space, or the router provides the shortest path information to the sending host, etc. The neighbor discovery function added to the ICMPv6 protocol that supports IPv6 addresses replaces the ARP protocol. ICMPvo also adds some new message types to support route optimization, IP multicast, mobile IP, etc. in IPv6.
7. ADSL usesfrequency division multiplexing technology to divide PSTN lines into three independent channels: voice, uplink and downlink, while providing Telephone and Internet service. Using ADSL networking, the computer needs to be connected to the telephone home junction box through ADSL Modem and a splitter.
8. TCP connection management three-way handshake. Since host A sends a connection request (SendSYN), the status of host B when receiving this request is SYN< a i=2> received. And since the sequence number sent by host A is 100, host B is ready to start receiving from 101 bytes.
9. The subnet mask of host routing is 255.255.255.255
10. Border Gateway Protocol BGP4 is a dynamic route discovery protocol. Its main function iscontrol routing policy. AS path information is transmitted between BGP routers, thus solving the routing loop problem. BGP4 messages are encapsulated inTCP messages
[Extension] Exterior Gateway Protocol BGP 4 is a dynamic route discovery protocol. Its main function is to control routing policies, such as whether it is willing to forward passing packets, etc. What is transmitted between BGP routers is AS path information, which consists of a target network address followed by a string of AS numbers to be passed through. If the same AS number appears in the string, a routing loop occurs.
BGP4 messages are encapsulated and transmitted in TCP messages. At the encapsulation level, it looks like an upper-layer protocol of TCP. However, functionally, it solves routing problems, so it still belongs to the network layer protocol.
11. In a broadcast network, the OSPF protocol selects a designated router (DR). The function of the designated router isto send link status announcements
[Extension] OSPF is a link state protocol used to exchange routing information between autonomous internal routers. The link state protocol collects link state information from each router, constructs a network topology diagram, and uses Dijkstra's Shortest Path First (SPF) algorithm to calculate the best route to each destination.
If two routers are connected to a common network through their respective interfaces, they are in a neighbor relationship. A router can select a router among its neighbors that needs to exchange link status information and establish an adjacency relationship with it. Not every pair of neighbors needs to exchange routing information, so not every pair of neighbors needs to establish an adjacency relationship. In a broadcast network or NBMA network, a Designated Router (DR) is elected. All other routers establish adjacency relationships with the DR and submit their own link status information to the DR, which releases it to the outside world on behalf of the network. . It can be seen that the existence of DR reduces the number of adjacency relationships, thereby also reducing the amount of routing information published to the outside.
OSPF routers exchange network topology information through Link State Advertisement (LSA). The LSA contains information such as the connected interface and link metric (Metric).
12. The POP3 protocol adopts the client/server mode. The client agent and the POP3 server are established through TCPconnection to transmit data.
[Extension] The POP3 protocol is a protocol used for mail reception in the TCP/IP protocol suite. The email client establishes a TCP connection with the server, using Client/ServerCalculation mode to send mail, port number110.
13. A legal domain name can be composed ofletters, numbers, and underscores, and no other characters other than the above three characters are allowed. , andcannot start and end with an underscore
14. Under Windows system, the allocated address is any address in the 169.254.0.0 segment. Therefore, the address in the 169.254.0.0 segment will not be the address assigned to the client by the DHCP server.
15, bottom row MIME unable to provide support layer safety
【extend】
S-HTTP is secure HTTP, which adopts a hypertext information protocol. It is generally used in Web browsing environments with high security requirements, such as e-commerce web browsing, payment through web pages, etc. It provides application layer security services. . HTTPS is SSL encrypted.
PGP is a protocol for transmitting secure emails. It can encrypt and sign emails. It provides application layer security services.
MIME (Multipurpose Internet Mail Extensions, Multipurpose Internet Mail Extensions) is a type of method that sets a file with a certain extension to be opened by an application. When the file with the extension is accessed, the browser will automatically use the specified application to open. It is mostly used to specify some client-defined file names and some media file opening methods. It does not provide any application layer security services.
SET (Secure Electronic Transaction, referred to as SET protocol) is mainly designed to solve credit card payment transactions between users, merchants and banks to ensure the confidentiality of payment information, the integrity of the payment process, and the legal identity of merchants and cardholders. , and operability. The core technologies in SET mainly include public key encryption, digital signatures, electronic envelopes, security certificates, etc. It provides application layer security services.
Therefore, the following services are provided:Application layer security:S-HTTP/PGP/SET