netstat this is a very useful utility that some system administrators are used every day, and some have to resort to it only to diagnose faults. But in any case, understanding this utility and being able to use it is very useful.
The command has only 10 parameters, of which probably the most frequently used is the parameter -a, which displays all connections and ports in use. However, even specifying parameters netstat from displays quite useful information.
Let us now consider the useful parameters of the utility netstat
Full domain name: When using the parameter -f full will be displayed domain names connected remote hosts. Any names will be resolved accessible ways. In the figure below you can see an example of this action:
Which process is using the open port: Using a combination of parameters -a -n -o You can track which process is using the open port. From the output of the command we find out the process identifier (PID), with which we can find the desired process in the task manager.
You can use another useful option to make the display more friendly. Parameter -b will show the name of each process, however it requires administrator rights.
Displaying the routing table: When using the parameter -r you can view the current routing table.
I most often use these 4 parameters for diagnostics Windows problems. How else do you use netstat and why?
Helpful information
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The Netstat command displays various network data such as network connections, routing table, interface statistics, masked connections, multicast space, etc.,
In this article, let's look at 10 practical command examples NetStat on Unix.
Regularly, some - only for diagnostics. I belong to the latter category: I prefer to use this utility to identify the causes of system problems and problems.
The netstat command has ten parameters that provide detailed information to solve the most difficult problems. different tasks. However, no less useful information can be obtained without any parameters.
The most common use of netstat is with the -a option to list all connections and listening ports. Listed below are a few other options that may come in handy when using this utility.
Fully qualified domain name. The -f parameter allows you to find out the FQDN for the external address. When using netstat with this option, names are resolved on both the internal and external networks. On fig. A shows the output of the command.
Figure A
Which process is using which port. The combination of the -a -n -o options allows you to find out which process identifier (PID) a particular port corresponds to. (See) The output of the command is shown in Fig. b.
Figure B
And if you add the -b option to this combination, friendly names will be used for each process, as shown in Fig. C. However, this will require administrator rights.
Figure C
Note: remote addresses pointing to 192.168.1.220:3261 belong to the Windows iSCSI Initiator service and are labeled differently than other service addresses.
Output of the routing table. When you want to figure out why a network connection is working differently on one computer than on others on the same network, you can use the -r option, which prints the route for that system, as shown in Figure 1. D. Please note the "Persistent routes" section: this lists all static routes configured for Windows Server).
Figure D
These four variations of the netstat command make it much easier
Sometimes during operation of any system, be it home Personal Computer or a powerful server serving many connections, it's useful to have a tool on hand that can display network activity data. Why might this be needed? To calculate applications that illegally access the Internet, or users. This is exactly what the utility we are considering does.
This is an application with which you can find out what is happening in this moment online. To start, use the command line. It also uses additional keys and parameters when starting Netstat.
It is worth noting that the name of the utility is formed from two components - network statistics, that is, network statistics, which, in principle, is logical. Among the information that the program shows, one can highlight routing connection statistics.
The syntax of command keys and parameters is quite extensive. This allows you to obtain network statistics at a variety of levels. The following is a description of the Netstat command, its parameters and keys:
To display command line all connections, while placing them on several pages, you need to use the following syntax: “-a | more". If you need to save all statistics to a specific file, you need to use “ -a > C:\filename”. Thus, all collected information will be written to the file specified in this path.
The result of the work can be a small table that contains the following types of data:
Netstat, launched with the -a and -b switches, will show all network connections, as well as the programs associated with them. This is very convenient if you need to figure out which program is actively using traffic and where it is sending data.
In addition to the above connection states, there are additional ones:
Using the utility in a Linux environment is, in fact, not much different from Windows. There are only slight differences in the command parameters. Description of the Netstat command and its parameters with examples:
Sometimes, in order to get more complete information about a network connection, you need to combine Netstat with some commands and Linux utilities. For example, like this:
netstat -ap | grep ssh
This line will display a list of ports that are currently used by the SSH utility. If, on the other hand, you want to find out which process is occupying a specific port, you can use the following syntax:
netstat -an | grep `:80`
Also for Netstat in Linux there is a universal set of keys that can display everything you need at once. It looks like this: netstat -lnptux. The data set will reflect all TCP, UDP, UNIX Socket protocols, names of processes and their identifiers.
The following command will let you know how many connections are active on each IP address:
netstat -naltp | grep ESTABLISHED | awk "(print $5)" | awk -F: "(print $1)" | sort -n | uniq -c
We define a large number of requests from one IP address:
netstat -na | grep:80 | sort
We determine the exact number of requests received per connection:
netstat -np | grep SYN_RECV | wc -l
When conducting a DoS attack, the number obtained as a result of this command should be quite large. In any case, it may depend on the specific system. That is, on one server it can be one thing, on another it can be different.
In which operating system Whatever the command is used, it is an indispensable tool for scanning, analyzing and debugging a network. It is actively used by system administrators all over the world.
Netstat can be used when the system is infected with some kind of virus software. It is able to show all applications with a lot of suspicious network traffic activity. This will help to identify malicious software at an early stage and neutralize it, or protect the server from unwanted intrusion by attackers.
The article gave detailed description Netstat command and its parameters and switches. Full use program is possible after several stages of practice on a real device. Combining with other teams will make it even more effective. Full set Descriptions of Netstat commands can be found in the manual on the utility's official website. It is also worth noting that when used in an environment Linux team Netstat is deprecated and SS is strongly recommended instead.
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