Linux 下测试 TCP|UDP 连通性

telnet和nc 是用来测试端口连通性的一般工具。
telnet可以测试tcp端口的连通性。
nc可以测试tcp和udp端口的连通性。
请确保telnet和nc工具已经安装

# yum install nc

# yum install telnet

测试tcp端口的连通性：
语法如下：

telnet <hostname/IP address> <port number>


如下是连通成功的例子：

# telnet 192.118.20.95 22

1. Trying 192.118.20.95…
2. Connected to 192.118.20.95.
3. Escape character is ‘^]’.
4. SSH-2.0-OpenSSH_6.6.1
5. Protocol mismatch.
6. Connection closed by foreign host.
7. 如下是连通不成功的例子：

1. # telnet 192.118.20.95 22
2. Trying 192.118.20.95…
3. telnet: connect to address 192.118.20.95: No route to host

使用nc命令来测试tcp端口的连通性：
语法：

nc -z -v <hostname/IP address> <port number>
如下是连通成功的例子：

1. # nc -z -v 192.118.20.95 22
2. Connection to 192.118.20.95 22 port [tcp/ssh] succeeded!

如下是连通不成功的例子：

1. # nc -z -v 192.118.20.95 22
2. nc: connect to 192.118.20.95 port 22 (tcp) failed: No route to host

使用nc命令来测试udp端口的连通性：
语法：

nc -z -v -u <hostname/IP address> <port number>

1. # nc -z -v -u 192.118.20.95 123
2. Connection to 192.118.20.95 123 port [udp/ntp] succeeded!