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I have installed Ubuntu 12.04 LTS.

Now, I want Internet connection sharing between the two LAN cards.

How can I accomplish this?

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You should connect one network card to a router with Internet connectivity and the other to a LAN. You Ubuntu system should be configured to provide so-called NAT service for the LAN. There are many guides to be found on the web, e.g., Google brings up:… – jdthood Jan 29 '13 at 13:26

Internet connection sharing in 12.04 is plug-n-play. However, there may be exceptions. Could you clarify your setup some more, like - What is the Internet connection? Which machine is connected to Internet and how? What are the connectivity options on the peer computers that need to connect via the share?

Basically, on the computer that will be connected to the Internet, you have to edit the LAN connection and select the IPv4 Settings method - "Shared to other computers" and also check "Available to all users". See below image.

Setup Internet Connection Sharing

Now, as soon as you hookup the peer computer to the above LAN connection, Internet is available.

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I have configured the system with DHCP. the NIC with DHCP can provide Ip to clients. Also under network manager I have set shared to other computers. But still the client cannot browse internet – user126959 Jan 30 '13 at 6:59
@Sri: AFAICT this disables the dhcp client on the adapter, which kills it's connectivity. The option shown appears to bridge the two connections, not NAT them, but it is insufficiently descriptive. Is there a way to NAT one connection onto another for connection sharing, via GUI? – nmr May 18 '14 at 21:00
How can I do this sharing using /etc/network/interface? – Dewsworld Sep 11 '14 at 11:30

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