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sources/tech/20170206 How to Check Remote Ports are Reachable Using nc Command.md

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+How to Check Remote Ports are Reachable Using ‘nc’ Command
+============================================================
+
+A port is a logical entity which acts as a endpoint of communication associated with an application or process on an Linux operating system. It is useful to know which ports are open and running services on a target machine before using them.
+
+We can easily [list open ports in Linux][3] on a local machine using the [netstat][4] or several other Linux commands such [NMAP][5].
+
+In this guide, we will show you how to determine if ports on a remote host are reachable/open using simple netcat (in short nc) command.
+
+netcat (or nc in short) is a powerful and easy-to-use utility that can be employed for just about anything in Linux in relation to TCP, UDP, or UNIX-domain sockets.
+
+```
+# yum install nc                  [On CentOS/RHEL]
+# dnf install nc                  [On Fedora 22+]
+$ sudo apt-get install netcat     [On Debian/Ubuntu]
+```
+
+We can use it to: open TCP connections, listen on arbitrary TCP and UDP ports, send UDP packets, do port scanning under both IPv4 and IPv6 and beyond.
+
+Using netcat, you can check if a single or multiple or a range of open ports as follows. The command below will help us see if the port 22 is open on the host 192.168.56.10:
+
+```
+$ nc -zv 192.168.1.15 22
+```
+
+In the command above, the flag:
+
+1.  `-z` – sets nc to simply scan for listening daemons, without actually sending any data to them.
+2.  `-v` – enables verbose mode.
+
+The next command will check if ports 80, 22 and 21 are open on the remote host 192.168.5.10 (we can use the hostname as well):
+nc -zv 192.168.56.10 80 22 21
+
+It is also possible to specify a range of ports to be scanned:’
+
+```
+$ nc -zv 192.168.56.10 20-80
+```
+
+For more examples and usage of netcat command, read through our articles as follows.
+
+1.  [Transfer Files Between Linux Servers Using netcat Command][1]
+2.  [Linux Network Configuration and Troubleshooting Commands][2]
+
+That’s all. In this article, we explained how to check if ports on a remote host are reachable/open using simple netcat commands. Make use of the comment section below to write back to us concerning about this tip.
+
+--------------------------------------------------------------------------------
+
+译者简介：
+
+Aaron Kili is a Linux and F.O.S.S enthusiast, an upcoming Linux SysAdmin, web developer, and currently a content creator for TecMint who loves working with computers and strongly believes in sharing knowledge.
+
+--------------------------------------------------------------------------------
+
+via: http://www.tecmint.com/check-remote-port-in-linux/
+
+作者：[Aaron Kili][a]
+译者：[译者ID](https://github.com/译者ID)
+校对：[校对者ID](https://github.com/校对者ID)
+
+本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出
+
+[a]:http://www.tecmint.com/author/aaronkili/
+
+[1]:http://www.tecmint.com/transfer-files-between-two-linux-machines/
+[2]:http://www.tecmint.com/linux-network-configuration-and-troubleshooting-commands/
+[3]:http://www.tecmint.com/find-open-ports-in-linux/
+[4]:http://www.tecmint.com/20-netstat-commands-for-linux-network-management/
+[5]:http://www.tecmint.com/nmap-command-examples/