Someone

debian:/etc/init.d# cat fire*
#!/bin/sh

PATH=/usr/sbin:/sbin:/bin:/usr/bin

#
# delete all existing rules.
#
iptables -F
iptables -t nat -F
iptables -t mangle -F
iptables -X

# Always accept loopback traffic
iptables -A INPUT -i lo -j ACCEPT


# Allow established connections, and those not coming from the outside
iptables -A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT
iptables -A INPUT -m state --state NEW -i ! eth1 -j ACCEPT
iptables -A FORWARD -i eth0 -o eth1 -m state --state ESTABLISHED,RELATED -j ACCEPT

# Allow outgoing connections from the LAN side.
iptables -A FORWARD -i eth1 -o eth0 -j ACCEPT

# Masquerade.
iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE
# Don't forward from the outside to the inside.
iptables -A FORWARD -i eth0 -o eth0 -j REJECT
iptables -A INPUT -p udp --sport 67 --dport 68 -j ACCEPT
iptables -A INPUT -p udp -j REJECT --reject-with icmp-port-unreachable
iptables -A INPUT -p icmp -j REJECT --reject-with icmp-port-unreachable
iptables -A INPUT -p tcp -j REJECT --reject-with tcp-reset
iptables -A INPUT -p tcp --dport 113 -j REJECT
/sbin/iptables -A INPUT -j REJECT

echo "1" >  /proc/sys/net/ipv4/ip_forward

debian:/etc/init.d# cat /proc/sys/net/ipv4/ip_forward
1
debian:/etc/init.d# ifconfig
eth0      Link encap:Ethernet  HWaddr 00:13:46:E1:EA:47
          inet addr:X.X.X.X  Bcast:X.X.X.X  Mask:255.255.255.0
          inet6 addr: fe80::213:46ff:fee1:ea47/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:10213 errors:0 dropped:0 overruns:0 frame:0
          TX packets:7074 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:7161170 (6.8 MiB)  TX bytes:761588 (743.7 KiB)
          Interrupt:10 Base address:0x3000

eth1      Link encap:Ethernet  HWaddr 00:50:BA:1A:C5:75
          inet addr:192.168.0.1  Bcast:192.168.0.255  Mask:255.255.255.0
          inet6 addr: fe80::250:baff:fe1a:c575/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:0 errors:0 dropped:0 overruns:0 frame:0
          TX packets:2605 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:0 (0.0 b)  TX bytes:124256 (121.3 KiB)
          Interrupt:9 Base address:0x3400

lo        Link encap:Local Loopback
          inet addr:127.0.0.1  Mask:255.0.0.0
          inet6 addr: ::1/128 Scope:Host
          UP LOOPBACK RUNNING  MTU:16436  Metric:1
          RX packets:550 errors:0 dropped:0 overruns:0 frame:0
          TX packets:550 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0
          RX bytes:66633 (65.0 KiB)  TX bytes:66633 (65.0 KiB)