Networking

Basics

For IP networks there are 2 address schemes, IPv4 and IPv6

ping <address>

Get response from <address> interface

for i in $(seq 1 254); do ping -c1 -t 1 10.117.192.$i; done

Scan a subnet

Check network connectivity

netstat -na # deprecated

ss -na

Show port status (LISTEN, ESTABLISHED, .....)

If you are root -p adds the process that owns the socket

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 ]    # 28 is the curl code for connection timeout
   then
    echo No connection to ${TARGET}:${PORT}
  fi
done

Interfaces

ifconfig -a # Deprecated, replaced by ip

Show all network interfaces

ifconfig <interface> <ipaddress>

Assign <ipaddress> to <interface>

ip address

Show all IP addresses

ip -6 address

Show all IPv6 addresses

ip -6 addr add <ipv6address>/<prefixlength> dev <interface>

Add an IPv6 address to <interface>

mii-tool <interface>

Show interface link status (speed)

When not using confusing things like NetworkManager network configuration is controlled by the interfaces file.

/etc/network/interfaces

auto <interface>             # Boot process waits until the interface is up or a time-out (5 minutes)
allow-hotplug <interface>    # Boot process does not wait for the interface.
iface <interface> inet dhcp
    wpa-ssid <ssid>
    wpa-psk <password>

# For static ipv4
interface <interface> inet static
    address xxx.xxx.xxx.xxx/<masklen>
    gateway xxx.xxx.xxx.xxx
# To have ipv6 auto-configured (by SLAAC)
iface <interface> inet6 auto

# To have ipv6 auto-configured (by SLAAC) and add own address
iface <interface> inet6 static
    address unique:local:address:prefix:your:own:host:address
    autoconf 1
    netmask 64

# Add another address to <interface>(work for IPv4 addresses too
iface <interface> inet6 static
    address unique:local:address:prefix:your:own:host:address
    netmask 64

# To have ipv6 auto-configured (by SLAAC) and query a dhcp-server
iface <interface> inet6 dhcp
    autoconf 1

Disable an interface completely (even not shown by ifconfig)

vi /etc/modprobe.d/blackllst.conf

Put in the driver for your interface like: blacklist ath9k

Wireless

iwscan <interface> scanning

Show available accesspoints

iwconfig <interface>

Show details of the wireless connection

Routing

route add -net default gw <IPaddress> # Deprecated

ip 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

traceroute <destination>

Show which route a package takes to reach destination

ip route get <IPaddress>

Show the interface used to go to <IPaddress>

To get just the interface name you can use this[1]:

host=<fqdn>
host_ip=$(getent ahosts "$host" | awk '{print $1; exit}')
ip route get "$host_ip" | grep -Po '(?<=(dev ))(\S+)'

Other

wget <URL>

Get the data from <URL>