Networking

Check network connectivity

netstat -nap

Show port status (LISTEN, ESTABLISHED, .....) and the program that owns it.

nc -v -z <host> <port>

Netcat: 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 -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 <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)

The interfaces file

apt-get purge network-manager
vi /etc/network/interfaces
auto <interface>
iface <interface> inet dhcp
    wpa-ssid <ssid>
    wpa-psk <password>

# To have ipv6 autoconfigured (by radvd) and add own addresses
iface <interface> inet6 static
    address unique:local:address:prefix:your:own:host:address
    autoconf 1
    netmask 64

For interfaces that may not be connected use allow-hotplug instead of auto.
The bootprocces now does not wait for an DCHP-answer on disconnected interfaces. Saves you about 5 minutes during startup.

Routing

route add -net default gw <IPaddress>

Add a default route using <IPaddress> as gateway

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.

Tracing

For tracing traffic see Tcpdump