About the author: Hello everyone, my name is Weiyang;
Blog homepage: Weiyang.303
Column series: multiple-choice questions for written examinations
Quote of the day: There is only one chance in a person's life to make a difference, and that is now! ! ! !
Preface
The last day of the written test training! ! ! ! ! ! ! ! ! !
1. Analysis of Day47 exercises (wrong questions)
1.
Analysis:
Question analysis:
Add the subnet mask and IP address to get the network number: 130.63.160.0
A:0~127，B:128~191-128.0~191.255；
130.63.160.2 is a Class B IP address. The network number occupies 2 bytes 130.63, and the subnet mask of the subnet indicates that the subnet network number occupies 3 bytes, so the subnet number is the third byte 160;
2.
Analysis:
Question analysis:
The IP protocol is used for routing selection, and ICMP is used for network status detection;
ARP is used to obtain IP from MAC; RARP is used from MAC to obtain IP; (note the distinction)
3.
Analysis:
Question analysis:
There are two header fields in the http protocol: Set-Cookie, Cookie;
Cookies are used for state maintenance of the http protocol. The server sends the state information that the client needs to carry in the next request through the cookie to the client for storage, and then reads it out and submits it to the server when the client requests it next time.
However, cookies are not secure, so using session , the server creates a session for each client to save the client status information, and hands the session ID to the client through the cookie, so that sensitive information is no longer transmitted through the cookie.
4.
Analysis:
Question analysis:
TIME_WAIT is the state that the active closing party enters after sending the last ACK. The purpose is to deal with the possible impact of the peer FIN retransmission caused by ACK loss on subsequent connections, and the waiting time is 2 msl time to ensure that even if there is Retransmission, all data of this communication disappears in the network;
5.
Analysis:
Question analysis:
The release of the connection in this question is not what we understand as closing the socket, but should be understood as sending a FIN request.
FIN means closing the connection request, but it should be noted that FIN only means that it will no longer send data, not that it will no longer receive data. The connection will be released after four waves. So B is wrong;
6.
Analysis:
Question analysis:
The sliding window mechanism is implemented based on the window size field. It is used by the receiver to tell the sender how much data to continue sending at most to avoid sending too many buffer overflows. The process of establishing a connection is a three-way handshake, and the process of disconnecting is a four-way wave. process;
TIME_WAIT is the state that will be entered by the active shutdown party. So D is wrong;
7.
Parsing: C
Question analysis:
Option A: tcpdump is used to capture packets from the network card;
Option B: top is used to view cpu resource usage;
Option C: netstat is used to view network communication connection status;
Option D: ifconfig is used to view network card information.
8.
Analysis:
Question analysis:
Known IP address, subnet mask, network number, broadcast address, valid host IP address;
Find the network number: Add the subnet mask and IP address to get the network number;
Find the host number: Invert the subnet mask to get the maximum host number. The broadcast address is the largest host number, that is, the host numbers are all 1. Find the effective IP address: The effective address allocation range is to remove the host number 0 and the maximum host number.
9.
Analysis:
Question analysis:
This question is similar to the previous one:
Known IP address, subnet mask, network number, broadcast address (host number)
The subnet mask and the IP address are combined to get the network number: 0101&11111100=4, so the network number is 172.16.100.4;
The composition of the IP address is the network number plus the host number, so the IP address minus the network number is the host number: 1;
10.
Analysis:
Question analysis:
Analysis of knowledge points:
Description of NAT mode:
NAT - network address translation technology , is used to set up a private network, assign private network addresses to hosts, and convert them to external public network addresses for external communication to save the use of public network addresses;
NAT implementation method: static - one-to-one fixed; dynamic - the conversion address is uncertain and dynamic conversion among multiple addresses;
Port multiplexing: Also called NAPT, a large number of hosts in a private network can use different ports with the same external address for external communication.
Option D: The addresses in the virtual machine are dynamically assigned by DHCP and do not require manual settings.
Summarize
