Linux Network troubleshooting and viewing network information commands

The ping command uses the ICMP protocol (echorequest----echo Reply package) to implement

Options

-C number of times you specify ping to exit

-W time Specifies maximum wait time

Note: If a large number of ping requests to the host, it will affect the other network services.

Ping Output Detailed

RTT: Response time for Request messages

error message:timeout keyword: there are 2 kinds of reasons:1, no this host 2, the other host does not respond

Target Host Unreachable: This goes to the RfC document (a good way to learn the network protocol is to look at the RfC ), there is a Chinese version!

Script to determine if the host is online:

1)

For: In.; Do ping–c1–w1 x.x.x. $i &>/dev/null && echo "online:x.x.x. $i" | | echo "Offline x.x.x. $i";d One

2)

For: In.; Do if ping–c1–w1x.x.x. $i &>/dev/null, then echo "online:x.x.x. $i", Else echo "offline x.x.x. $i"; fi;done

3) Quick Ping method

For: In.; Do (Ping–c1–w1 x.x.x. $i &>/dev/null && echo "online:x.x.x. $i" | | echo "offlinex.x.x. $i") &;d one|sort–t.-n–k4

Traceroute Command: How many router to track to the target host

TCP Finite state machine: identifies the status of a connection that is based on a TCP protocol--- see the picture under the Mag Learning Note Directory with the same name

Netstat command options

-T view TCP established connections

- u View the UCP established connection

-A = =-tu

-P Display Pid/ program name

-rn show local routing table (no reverse domain name)

-L Show services in listening state

-N Displays the port number, hostname (IP) in numeric format,does not reverse IP, does not resolve the service name corresponding to the port number

* common option combination -TUNLP *udp is not connected so there is no LISTEN this state,

available options -tn | -TNL display only TCP connection information

• The-C option displays the output and does not exit the command, you can dynamically display the connection status, available commands #netstat –TNC 5 Try it, this command specifies that the refresh time is refreshed every 5 seconds, and does not specify that the default is refreshed every second.

-E Displays extended information, such as user inode columns and many more,-tne options Try

The netstat command executes slowly while the native has a large number of connections, the SS command is provided by the Iproute2 package, the function type netstat, Performs faster than Netstat when the machine has a large number of connections

SS Command Options

-T view TCP established connections

-t-a View TCP established connections , and services in the listener

- u View the UCP established connection

-u-a View The UCP is connected and the service waiting to connect

Common Options –tua

-l display sockets in listening

-m displays memory information used by sockets

-e display extended information

-S Display statistics

-P Display Pid/ program name

The SS can also specify a filter condition to display the connection #man SS

Cases

Ss-ta State established ' (Dport =:ssh) '

Ss-tan State established ' (dport =:22 or sport =: 22) '

This article from the "Let me more Hungry" blog, please be sure to keep this source http://ufirst.blog.51cto.com/7628670/1432611