Linux Operations (Network interview topics)

1. What is the difference between a switch and a hub?

The main difference:

Hub: 20 gigabit broadband Four PCs connected to the hub via a network cable, then each PC can only use five gigabit broadband

Switch: 20 gigabit broadband Four PCs connected to the switch via a network cable, then every PC can use 20 broadband

Summary: Hub 20 gigabit Broadband is used by multiple ports, using shared broadband working mode

The switch is a unique channel that ensures that each port uses 20 gigabit Broadband

2, VMware workstation three kinds of Internet mode (bridge mode, Nat mode, only host mode what is the difference)?

Bridge mode: Equivalent to virtual out of the LAN in a separate PC, he and the LAN PC is the equivalent of the relationship, so choose the bridge mode, your network segment should be set in the same network segment and gateway

Nat mode: is to have the virtual machine with NAT (Network address translation) function, through the Ruthenica host network to access the public network. As we connect the router to the Internet in the LAN, our IP will become a 1.0 network segment, that is, a NAT conversion,

This time, the local area network PC can not make use of my laptop, but my notebook computer through the router to get through the LAN on any of the PC, and the virtual Machine bridge mode is this way to the Internet, through my things

Rich to the Internet, your physical machine is the equivalent of making a router

Host-only mode: The real environment and virtual machines are isolated, you in this mode, all of your virtual machines can be interconnected, virtual machines can be connected with your physical machine, the equivalent of their twisted pair, but the virtual machine system and

The real network is isolated, so you choose only the host mode, you can not go to the extranet

Summary: Do the experiment process often need to use the external network, so only the host mode can not be used, and some companies he is to be bound by the MAC address of your machine you can go to the Internet, so your bridge mode can not be used, and finally we can only

Nat mode to go to the Internet, so we keep good habits, virtual machines do experiments are using NAT mode

3, the TCP port status established, Time_wait, close_wait, time_wait, syn_sent respectively mean what? How to optimize time_wait

Established status: Connection already established. Indicates that two machines are communicating.

Time_wait: We actively call Close () to disconnect and the status becomes time_wait after receiving confirmation from the other party.

Close_wait: When the other side actively shuts down the connection or the network exception causes the connection to be interrupted, our state becomes close_wait at this time we want to call Close () to make the connection close properly

Syn_sent: Indicates a request connection

The network has slowed down. The first thing is, NETSTAT-A | grep time_wait | Wc-l, ah Ma, thousands of time_wait.

Net.ipv4.tcp_tw_recycle = 1

Net.ipv4.tcp_tw_reuse = 1

Net.ipv4.tcp_timestamps = 1

4. "." In the shell What is the difference from "source"?

A new shell is created, and then the corresponding script is executed.

Source is executed under the current shell and no longer enabled for other shells

5. What is the difference between TCP and UDP?

TCP is a connection-oriented, reliable byte-stream service

UDP is a non-connected, unreliable datagram service

6. What are the seven layers of the OSI seven layer protocol?

Physical layer, Data link layer, network layer, transport layer, Session layer, presentation layer, application layer

7, what is the four layer of TCP/IP four-layer association?

Network interface layer, internetwork layer, Transport layer, application layer

8, tell me about the classification of IP address?

Class A address: 10.0.0.0-126.255.255.255 default subnet Mask code/8, which is 255.0.0.0 (where 127.0.0.0~127.255.255.255 is the loopback address for local loopback testing, etc.)

Class B Address: 128.0.0.0-191.255.255.255 default subnet mask/16, or 255.255.0.0

Class C Address: 192.0.0.0-223.255.255.255 default subnet mask/24, which is 255.255.255.0

Class D Address: 224.0.0.0-239.255.255.255 is generally used for multicast

Class E Address: 240.0.0.0-255.255.255.255 e-class address is generally used for research purposes (where 255.255.255.255 is a full-network broadcast address)

9. What is a router?

Router is a device that connects LAN and WAN in the Internet, also known as Gateway device

is used to connect multiple logically separated networks, so-called logical networks represent a single network or subnet. When data is transferred from one subnet to another subnet, it can be done through the router's routing capability.

10. What is the difference between a two-tier switch and a three-tier switch?

The two-tier switch is only enabled by the switch

Three-layer switch with switching function and routing function

11, TCP/IP, what are the corresponding protocols for each layer?

Network layer: IP protocol, ICMP protocol, ARP protocol, RARP protocol

Transport layer: UDP protocol, TCP protocol

Application layer: FTP (File Transfer Protocol), Telnet (remote login Protocol), DNS (Domain name Resolution Protocol), SMTP (Mail Transfer Protocol), POP3 Protocol (Post Office Protocol), HTTP protocol

12. What are the routing devices and related layers?

Physical layer: Repeater, hub

Data Link layer: Bridge, switch

Network layer: Router

Gateway: Devices above the network layer

13, explain the server these kinds of digital error meaning 200, 201, 400, 401, 403, 404, 405, 413, 414, 500, 501, 502, 503, 504, 505?

2001 Cut Normal

301 Permanent Jump

400 A syntax error occurred in the request

401 Customer attempts to access password-protected pages without authorization

403 Forbidden, resource unavailable, usually due to server file or directory permissions settings.

404 Unable to find a resource at the specified location

405 The request method does not apply to the specified resource

406 The specified resource has been found, but it has a MIME type and is incompatible with the client specified in the Accpet header

414 The requested URL is too long

500 Internal server error, server encountered unexpected situation, generally for program problems

501 The server does not support the functionality required to implement the request

502 bad gateways, typically when the gateway server requests the backend service, the backend service does not return the results correctly as the HTTP protocol

503 Server failed to answer due to maintenance or heavy load

504 Network timeout, when the gateway server is typically requesting a backend service, and the end service does not complete the task in a specific time period

505 the HTTP version indicated in the request is not supported by the server

14. Describe the detailed process of TCP "three-time handshake" and "four disconnection"?

Three-time handshake:

First handshake: Host a establishes a connection to Host B request (SYN),

Second handshake: When Host B receives a request from host A, it responds to host A with a data segment with a ACK (ACK) and a synchronous sequence number (SYN) flag bit.

Third handshake: When host a receives this data segment, it sends a confirmation reply (SYN) confirming that it has received the data segment of Host B

Four-time disconnection:

First disconnection: When host a completes the data transfer, the control bit fin is set to 1 and a request to stop the TCP connection is made

Second Disconnect: Host B responds to the fin after receiving it, confirming that the TCP connection to the side is closed and the ACK is set to 1

Third disconnection: The end of the second direction by the B-terminal request, the fin 1

Fourth disconnect: Host a confirms the request to host B, placing the ACK at 1 and closing the two-direction closure.

15, with tcpdump command monitoring 192.168.1.1 host and 80 port?

Tcpdump-vnn-i any host 192.168.1.1 and port 80

16, how to solve the network failure of the server?

The Lord uses Ping, traceroute, dig, Nslookup to disable the barrier. Also check the IP, gateway, and DNS configuration

17. The DNS server you know

223.5.5.5 Telecom, Hangzhou, Zhejiang, China

223.6.6.6 Telecom, Hangzhou, Zhejiang, China

202.96.128.86 Guangdong province Guangzhou Telecom

202.96.128.166 Guangdong province Guangzhou Telecom

114.114.114.114 Jiangsu Province Nanjing Telecom

This article is from the "Wsyht blog" blog, make sure to keep this source http://wsyht2015.blog.51cto.com/9014030/1786892

Linux Operations (Network interview topics)