A summary of confusing knowledge points for soft-Test network engineers

Network Engineer Examination is the National computer technology and software level examination of an intermediate qualification examination, through the examination of qualified personnel in accordance with the requirements of the application Department of network system planning, design and installation of network equipment and hardware debugging work, can carry out network system operation, maintenance and management, can be efficient, reliable, Manage network resources securely, as a network professional to the system development of technical support and guidance, with the actual work ability of engineers and business level, can guide network administrators to engage in network system construction and management work. Network Engineer Exam is a popular soft test, how to pass the exam is the vast number of candidates want to know, the following Greek soft test college for you to bring the network engineer to prepare for the Battle of the test, professional teachers to arrange the network engineers exam easy to confuse the knowledge points, help you preparation.

The Network Engineer examination easily confuses the knowledge point summary

1, data encoding-original code, anti-code and complement

Original code: The value is preceded by a sign bit (that is, the highest bit is the sign bit), the bit is 0 when the positive number, 1 is negative, and the rest of you represent the size of the value.

Anti-code: The inverse code of positive number is the same as the original code, minus the anti-code sign bit is 1, the rest of you for the absolute value of the original code bitwise negation.

Complement: Positive complement is the same as the original code, the complement of negative numbers is the number of anti-code plus 1, this plus 1 is "fill."

2. Addressing mode-immediate addressing and direct addressing

Immediate addressing: The immediate addressing method usually gives the operand directly in the Address Code section of the instruction.

Direct addressing: The main memory address of the operand or operation result of the participating operation is given directly in the instruction.

3. High-level language-interpreter and compiler program

Interpreter: The explanation method refers to the source program to enter the computer, explain the program side scanning side interpretation, stepping into the sentence-by-step translation, the computer is executed, does not produce the target program

Compiler: When a user writes a source program written in a high-level language to a computer, the compiler translates the source program into a target program that is equivalent to the machine language, and then the computer executes the target program.

4. File Management-relative path and absolute path

Relative path: An absolute path is a path that starts at the root, also known as a full path

Absolute path: A relative path is a path that starts from the user's working directory.

5. Project Management-Gantt Chart and plan review chart

Gantt Chart: Use horizontal segments to represent the work phase of a task, where the start and end points of the segment correspond to the start and finish times of the task, and the length of the segment indicates the time required to complete the task.

Plan review diagram: A PERT chart is a network model that describes the relationship between a project task. You can clearly express the dependencies between tasks, that is, which tasks are completed before other tasks can be started, and the critical path to complete the project as scheduled.

6. Data Communication-Nyquist theorem, Shannon theorem and Nyquist sampling theorem

Nyquist theorem: The formula for the transfer rate of the highest code in the case of an ideal channel: b=2w

Shannon theorem: In the actual channel, the limit data transmission rate c=wlog2 (1+s/n)

Nyquist sampling theorem: Every time interval, the current value of the analog signal is taken as a sample, which represents the instantaneous value of the analog signal at a certain moment. Nyquist sampling theorem: If the sampling rate is greater than twice times the maximum frequency of the analog signal, the original analog signal can be recovered from the obtained sample.

7. Data Encoding-Manchester code and differential Manchester code

Manchester code: Manchester Code is a bi-phase code that uses low to high level transitions to represent 0, with a high to low level transition representing 1 (or vice versa)

Differential Manchester code: The difference Manchester code is based on the Manchester code to add the Flip feature, when 0 flip, 1 unchanged

8. Twisted pair -568a and 568B

568A: White green | green | white ORANGE | blue | white BLUE | orange | White Brown | brown

568B: White Orange | orange | white GREEN | blue | white BLUE | green | white Brown | brown

9. LAN Technology-conflict domain and broadcast domain

Conflict Domain: 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.

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.

10. Switch-Stack and cascade

Stacking: Stacking requires dedicated stacking modules and stacking cables

Cascade: Cascade can be done between switches of any network device manufacturer via a twisted pair.

11. PPP authentication method-PAP and Chap

The PAP:PAP certification process uses two-time handshake mechanisms. Send user name and password in clear text format

Chap:chap does not send a plaintext password on the line, but sends a random sequence processed by the digest algorithm, at the same time, the identity authentication can be carried out at any time, including during the normal communication between the two parties.

12, Flow control-choose to re-send Arq and back N-Frame Arq

Choose to re-send ARQ: In order to avoid the exception, the window maximum is less than half of the total number of frame numbering, that is, W hair =w receive ≤2k-1.

Back N-Frame ARQ: To avoid exceptions, you must limit the size of the sending window W≤2k-1 (K is the number of bits in the frame number).

13. Broadcast address-restricted broadcast address and direct broadcast address

Restricted broadcast: It is not routed, but the network fields and host fields that are sent to all host IP addresses on the same physical network segment are all 1 and address 255.255.255.255

Direct broadcast: The network broadcast is routed and sent to the network field of each host IP address on the dedicated network to define the network, and the host fields are typically all 1, such as 192.168.10.255

14. ICMP protocol-Endpoint unreachable and time exceeded message

Destination Unreachable: When the host or router fails to deliver the datagram, it sends an endpoint unreachable message to the source point.

Time exceeded: When the router receives a time-to-live-zero datagram, it sends more time than the message to the source station, in addition to discarding the datagram.

15. SNMP Protocol-161 ports and 162 ports

161 Port: Use 161 ports on the server where the agent is running to receive get or set messages and send response messages

162 Port: The client running the hypervisor receives a trap message from each agent using the well-known port 162来.

16, Linux system DNS configuration-/etc/hosts and/etc/host.conf

The format of the-/etc/hosts:hosts table is an IP address on the left and the name corresponding to the IP address on the right.

The contents of the/etc/host.conf:/etc/host.conf file determine the order of parsing, for example, first with the hosts table, or with DNS parsing.

17. Routing Basics-manage distances and metrics

Administrative distance: a route that has a higher priority than other routes is called managed distance AD. The main reason is to compare the parameters of different routing protocols to the destination network, the smaller the ad value, the higher the confidence level of this route.

Measure: measure represents distance. They are used to determine the optimal routing path when looking for a route. Each routing algorithm generates a numeric value (measure) for each path through the network when the routing table is generated, and the minimum value represents the optimal path.

18. ipsec-tunnel mode and transmission mode

Tunnel mode: In transport mode, the IPSec header is incremented between the original IP header and the data, and some control fields are added after the entire transport beginning segment and signed to form an IPSec datagram. This approach is to protect the entire transmission beginning paragraph. Therefore, the security of the data portion of the original IP packet can only be guaranteed

Transport mode: Tunnel mode provides a secure transport mechanism for the entire IP packet. is to add some control fields behind and in front of an IP datagram to form an IPSec datagram.

A summary of confusing knowledge points for soft-Test network engineers