Networking

Check network connections

Netcat

nc -v -z <host> <port>

Tell me if we can open a connection to <host> on <port>. Without -z it works like telnet

nc -v -u -z <host> <port>

Tell me if we can open a connection to <host> on a UDP <port>

Curl

curl -vvv -k --proxy1.0 <proxyIP>:<proxyPort> <Remote URL>

Get the data from <remote URL> via <proxyIP> -k allows insecure SSL connections

curl -vvv telnet://<IP>:<port>

Just test connectivity to a port

Wget

wget <URL>

Get the data from <URL>

openssl

openssl s_client -showcerts -connect <IP>:443

Test SSL connection

Tunneling

ssh -L 8080:remotehost:3006 proxy

Login over ssh to proxy and there connect to remotehost port 3306. Connect local port 8080 to the remote connection.

Now if you connect to port 8080 on your local server you are connected to port 3306 on the remotehost

Using -nNT prevents that the ssh command opens a terminal on the proxy. The ssh command however must remain active.