方式1：telnet host port
telnet 118.31.63.105 9999
方式2：nc -v host port
方式3：ssh -v -p port username@ip
-v 调试模式(会打印日志).
-p 指定端口
username可以随意
连接不存在端口
[wyq@localhost ~]$ ssh -v -p 9000 wyq@localhost
OpenSSH_6.4, OpenSSL 1.0.1e-fips 11 Feb 2013
debug1: Reading configuration data /home/wyq/.ssh/config
debug1: Reading configuration data /etc/ssh/ssh_config
debug1: /etc/ssh/ssh_config line 51: Applying options for *
debug1: Connecting to localhost [127.0.0.1] port 9000.
debug1: connect to address 127.0.0.1 port 9000: Connection refused
ssh: connect to host localhost port 9000: Connection refused
"Connection refused"表示端口不可用
连接存在的端口
[wyq@localhost ~]$ ssh -v -p 8080 wyq@localhost
OpenSSH_6.4, OpenSSL 1.0.1e-fips 11 Feb 2013
debug1: Reading configuration data /home/wyq/.ssh/config
debug1: Reading configuration data /etc/ssh/ssh_config
debug1: /etc/ssh/ssh_config line 51: Applying options for *
debug1: Connecting to localhost [127.0.0.1] port 8080.
debug1: Connection established.
debug1: identity file /home/wyq/.ssh/id_rsa type 1
debug1: identity file /home/wyq/.ssh/id_rsa-cert type -1
debug1: identity file /home/wyq/.ssh/id_dsa type -1
debug1: identity file /home/wyq/.ssh/id_dsa-cert type -1
debug1: identity file /home/wyq/.ssh/id_ecdsa type -1
debug1: identity file /home/wyq/.ssh/id_ecdsa-cert type -1
debug1: Enabling compatibility mode for protocol 2.0
debug1: Local version string SSH-2.0-OpenSSH_6.4
debug1: ssh_exchange_identification: <head>
debug1: ssh_exchange_identification: <title>Error response</title>
debug1: ssh_exchange_identification: </head>
debug1: ssh_exchange_identification: <body>
debug1: ssh_exchange_identification: <h1>Error response</h1>
debug1: ssh_exchange_identification: <p>Error code 400.
debug1: ssh_exchange_identification: <p>Message: Bad request syntax ('SSH-2.0-OpenSSH_6.4').
debug1: ssh_exchange_identification: <p>Error code explanation: 400 = Bad request syntax or unsupported method.
debug1: ssh_exchange_identification: </body>
ssh_exchange_identification: Connection closed by remote host
"Connection established" 表示已经连上端口
