Networking

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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
#!/bin/bash
 
PORT=$1
 
TARGETS="999.999.999.999
888.888.888.888
777.777.777.777
666.666.666.666
"
 
for TARGET in ${TARGETS}
do
  curl  http://${TARGET}:${PORT} --connect-timeout 1 > /dev/null 2>&1
  if [ $? == 28 ]
   then
    echo No connection to ${TARGET}:${PORT}
  fi
done

Wget

wget <URL>
Get the data from <URL>

OpenSSL

See the OpenSSL page

Interfaces

ifconfig -a
Show all network interfaces
ifconfig <interface> <ipaddrss>
Assign <ipaddress> to <interface>
mii-tool <interface>
Show interface link status (speed)

Tunneling

ssh -L 8080:remotehost:3006 proxy
Login over ssh to proxy and there connect to remotehost port 3006. Connect local port 8080 to the remote connection.
Now if you connect to port 8080 on your local server you are connected to port 3006 on the remotehost
Using -nNT prevents that the ssh command opens a terminal on the proxy. The ssh command however must remain active.