ip addr show
ip addr show eth0

ip route show

cat /etc/resolv.conf

netstat -i
netstat -ia
# ss -s
# ss -l
# ss -t -a
# ss -u -a

ss -s
ss -l
ss -lp | grep 4949

netstat --listen # netstat command to find open ports
netstat -vatn # To display open ports and established TCP connections, enter:
netstat -vaun # To display only open UDP ports try the following command:
netstat -vat # If you want to see FQDN (full dns hostname), try removing the -n flag:
$
lsof Command Examples

lsof -i # To display the list of open ports, enter:
lsof -i 4 -a -p 9255 # To display all open IPv4 network files in use by
# the process whose PID is 9255, use:

A Note About FreeBSD Users
You can use the sockstat command lists open Internet or UNIX domain sockets, enter:
sockstat
sockstat -l
sockstat -4 -l
sockstat -6 -l

# -----------------------------------------------------------
# -----------------------------------------------------------
# --- NAT router
#
route
route -n
ip route show
ip route list
route add default gw 192.168.1.254 eth0
ip route add 192.168.1.0/24 dev eth0
# ---
route add default gw 192.168.0.1
route
# --- Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
# --- 192.168.0.0     *               255.255.255.0   U     0      0        0 eth0
# --- default         192.168.0.1     0.0.0.0         UG    0      0        0 eth0
route add default gw 192.168.0.1
echo 1 > /proc/sys/net/ipv4/ip_forward
iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE
iptables -A FORWARD -i eth1 -j ACCEPT
# ---
apt-get install dnsmasq
# -----------------------------------------------------------
# --- 1. NAT Scripts
#
#!/usr/bin/env bash
modprobe iptable_nat
echo 1 > /proc/sys/net/ipv4/ip_forward
ifconfig eth1 192.168.0.1 netmask 255.255.255.0
iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE
iptables -A FORWARD -i eth1 -j ACCEPT
# -----------------------------------------------------------
# --- 1. NAT Scripts
# --- File: /etc/network/interfaces
#
iface eth0 inet static

       up route add -host 255.255.255.255 eth0

# -----------------------------------------------------------


http://www.cyberciti.biz/faq/linux-route-add/
# --- 2. NAT Scripts
#!/usr/bin/env bash
ifconfig eth0 down
ifconfig eth0 192.168.0.2 netmask 255.255.255.0
route del -net default 2>/dev/null
route add default gw 192.168.0.1 2>/dev/null
echo "nameserver xx.xx.xx.xx" > /etc/resolv.conf

# -----------------------------------------------------------
# -----------------------------------------------------------
# --- NETWORK monitooring
#
iftop -i wlan0
iptraf
goaccess -f other_vhosts_access.log
http://server.dzone.com/articles/6-command-line-tools-linux
http://www.cyberciti.biz/tips/top-linux-monitoring-tools.html
http://archive09.linux.com/feature/138744?theme=print
http://kirrus.co.uk/2009/11/network-monitoring/
http://www.techofy.org/2012/09/glances-cli-curses-based-system.html
# # # # # | http://nmon.sourceforge.net/pmwiki.php