How to share ADSL with linux?

tadziu23 · 11-16-2005, 12:43 PM

well i guess this forum is my last chance

i've got adsl net connection on usb sagem modem,
and i want to share it with two computers in my
home. i'v got two ethernet cards in linux based
machine (connected to net by usb modem), networked
with other 2 machines by crossover cables.
pinging all 2 computer's works fine, pinging
yahoo.com also works, so all connections are set.
but sharing is not

how to set dhcp.conf?
how to set iptables?

my ifconfig:

Code:

eth0      Link encap:Ethernet  HWaddr 00:08:54:02:E6:D1
          inet addr:100.100.100.40  Bcast:100.100.100.255  Mask:255.255.255.0
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:0 errors:0 dropped:0 overruns:0 frame:0
          TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:0 (0.0 b)  TX bytes:0 (0.0 b)
          Interrupt:10 Base address:0xf00

eth1      Link encap:Ethernet  HWaddr 00:50:BF:4D:50:01
          inet addr:100.100.100.30  Bcast:100.100.100.255  Mask:255.255.255.0
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:24 errors:0 dropped:0 overruns:0 frame:0
          TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:2184 (2.1 Kb)  TX bytes:0 (0.0 b)
          Interrupt:12 Base address:0x2e00

lo        Link encap:Local Loopback
          inet addr:127.0.0.1  Mask:255.0.0.0
          UP LOOPBACK RUNNING  MTU:16436  Metric:1
          RX packets:0 errors:0 dropped:0 overruns:0 frame:0
          TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0
          RX bytes:0 (0.0 b)  TX bytes:0 (0.0 b)

ppp0      Link encap:Point-to-Point Protocol
          inet addr:83.23.25.43  P-t-P:213.25.2.40  Mask:255.255.255.255
          UP POINTOPOINT RUNNING NOARP MULTICAST  MTU:1492  Metric:1
          RX packets:1042 errors:0 dropped:0 overruns:0 frame:0
          TX packets:1156 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:3
          RX bytes:464936 (454.0 Kb)  TX bytes:130931 (127.8 Kb)

(ppp0
is my usb-modem connection with ISP's settings. )

if someone could tell my how to do it or knows some
newbie's-friendly 'howto' set such sharing, please, please
please help

nephish · 11-16-2005, 01:37 PM

what distrobution of linux do you use?
the reason i ask, is that firestarter (for gnome but can be used outside of gnome)
is a great little utility that i used to set up my firewall and server at home.
it has a very newbie friendly interface and setup wizard and takes care of iptables and rules for you.

Andrew Benton · 11-16-2005, 01:53 PM

I don't use dhcp, I configure the computers here with static addresses. I share my ADSL connection with my daughters laptop with these iptables rules. They depend on some kernel functionality so either compile it in or load the modules.

Code:

#!/bin/bash
iptables -A INPUT  -i lo -j ACCEPT
iptables -A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT
iptables -P INPUT DROP
iptables -P FORWARD DROP
iptables -P OUTPUT ACCEPT
iptables -t nat -A POSTROUTING -o ppp0 -s 192.168.1.4/32 -j MASQUERADE
iptables -A INPUT -s 192.168.1.4/32 -j ACCEPT
iptables -A FORWARD -i ppp0 -o ppp0 -j DROP
iptables -A FORWARD -i ppp0 -o eth0 -j ACCEPT
iptables -A FORWARD -i eth0 -o ppp0 -j ACCEPT

And I don't have net tools (ifconfig) installed, I use iproute, but it's more or less the same

Code:

ip addr add 192.168.1.3/24 dev eth0 &&
ip link set eth0 up &&
ip route add 192.168.1.4 dev eth0 &&
echo 1 > /proc/sys/net/ipv4/ip_forward

My computers 192.168.1.3, my daughters laptop is 192.168.1.4. I don't think you need the `link set up'command with ifconfig. Hope that helps.

tadziu23 · 11-16-2005, 04:19 PM

i use slack.

if above's sollution won't work, i'll try firestarter then
(hope it works with K)...
regards