Configuración de red de dos tarjetas en Ubuntu

Autor: @javcasta
Función: Script que configura 2 tarjetas de red.

#!/bin/bash
# Script de configuracion de red, DNSs, ruta por defecto y llamada a reglas de IpTables

# RED
# parametros de red
ipeth0=10.50.66.3;masketh0=255.255.255.0;redeth0=10.50.66.0;broadcasteth0=10.50.66.255;gweth0=10.50.66.1
ipeth1=192.168.1.1;masketh1=255.255.255.0;redeth1=192.168.1.0;broadcasteth1=192.168.1.255
echo Configurando los interfaces de red y el DNS. ...
echo "auto lo" > /etc/network/interfaces
echo "iface lo inet loopback" >> /etc/network/interfaces
echo "# eth0 interfaz conectado al router" >> /etc/network/interfaces
echo "auto eth0" >> /etc/network/interfaces
echo "iface eth0 inet static" >> /etc/network/interfaces
echo "        address $ipeth0" >> /etc/network/interfaces
echo "        netmask $masketh0" >> /etc/network/interfaces
echo "        network $redeth0" >> /etc/network/interfaces
echo "        broadcast $broadcasteth0" >> /etc/network/interfaces
echo "        gateway $gweth0" >> /etc/network/interfaces
echo "# eth1 interfaz conectado a la LAN" >> /etc/network/interfaces
echo "auto eth1" >> /etc/network/interfaces
echo "iface eth1 inet static" >> /etc/network/interfaces
echo "        address $ipeth1" >> /etc/network/interfaces
echo "        netmask $masketh1" >> /etc/network/interfaces
echo "        network $redeth1" >> /etc/network/interfaces
echo "        broadcast $broadcasteth1" >> /etc/network/interfaces
echo "# Ruta de ultimo recurso" >> /etc/network/interfaces
echo "up route add -net 0.0.0.0/0 gw $gweth0 dev eth0" >> /etc/network/interfaces
echo "# aplicamos reglas de iptables" >> /etc/network/interfaces
echo "pre-up iptables-restore < /home/usuario/scripts/iptables.reglas.javcasta.up" >> /etc/network/interfaces
echo "# ---- by javcasta - 2.011 - http://javcasta.com ---" >> /etc/network/interfaces
# DNSs
dns1=208.67.222.222
dns2=208.67.220.220
nombreservidor=$(hostname -s)
dominio=$(hostname -d)
echo "# by script - 2.011" > /etc/resolv.conf
echo "search $dominio" >> /etc/resolv.conf
echo "domain $dominio" >> /etc/resolv.conf
echo "nameserver $dns1" >> /etc/resolv.conf
echo "nameserver $dns2" >> /etc/resolv.conf
# habilitar enrutamiento
echo "1" > /proc/sys/net/ipv4/ip_forward
# reiniciamos servicio de red
#service networking restart
/etc/init.d/networking restart

Configura lo siguiente:

Los parámetros tcp/ip de las dos tarjetas (NICs)

Los DNs

La ruta por defecto o de último recurso

La llamada a un script de ipTables

Habilitar el enrutamiento