Share Internet Connection from GNU/Linux Systems

Saturday, 2. November 2013

this is a direct copy of http://saikatbasak.com/share-internet-connection/  Thank you for this neat howto!

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Now, here we have,

A computer connected to the Internet via the eth0 port (if you have a mobile broadband it would be ppp0).

We want to share the connection via the eth1 port of the same computer.

What we need,

We need basic networking utilities that is, in most cases, comes pre-installed in your GNU/Linux distribution (iptablesifconfig to be precise).

Yes, we do need some Lan Cables (Crossover cable) to share the connection via the eth1 port of the above mentioned computer.

So, let us begin. Connect your computer to the Internet. If u have a dhcp connection you may use dhclient or dhcpcd. Just do, as root, ‘dhclient eth0′, without the quotes. For connecting to mobile broadband you may use wvdial.

Flush iptables rules:

# iptables -F
# iptables -t nat -F
# iptables -t mangle -F
# iptables -X
# iptables -t nat -X
# iptables -t mangle -X

Enable kernel routing mode:

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

Also, you can make ip forward permanent by editing /etc/sysctl.conf and set net.ipv4.ip_forward = 1

Setup eth1:

# ifconfig eth1 10.10.10.1 netmask 255.255.255.0
# ifconfig eth1 up

( you may consider using a different ip address)

Set iptables rules for port forwarding:

# iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE

That’s it. Now connect one end of the cable to the eth1 port of your server. Connect the other end to any computer or device such as a router or a switch.

Client side configuration example:

Ip address: 10.10.10.2
netmask: 255.255.255.0
gateway: 10.10.10.1
DNS server address: Same as the server (you may also use Google DNS or any other DNS of your preference)

# ifconfig eth0 10.10.10.2 netmask 255.255.255.0
# ifconfig eth0 up
# route add default gw 10.10.10.1 eth0
# echo "nameserver 8.8.8.8" > /etc/resolv.conf

Happy surfing.

 

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