Few months back my cousin, moved to live at home so second PC came at home and i had to look how to setup a HAN (Home Area Network 
) and share internet illegally. There were two problems - first, i was doing it for first time and second, if i could not to spend any money for additional devices.
Long ago when i drop from dial-up to internet over LAN i had to buy a PCI LAN adapter (those times, build-in network adapters were more as extra than standart part of modern mobos). Now, several years later with upgraded mobo you always get network adapter, its just like the build-in sound device - its always included in the mobo. So i found myself with my old LAN adapter and a build-in gigabit adapter that i havent used so far. Then i just needed a cross-over cable that i found in my cousin old flat cutting it with a kitchen knife from the wall. So i only had to buy few RJ45 connectors which are cheep.
Now i had 16m long cable (cause the second pc is at the other end of the flat), build-in gigabit adapter enabled and computers - connected to each other. I had to find a way to hide the second pc from my ISP - you know they want you to pay to be able to connect a second pc at home to internet. My current internet provider have connected me in a huge LAN and through additional PPPoE each pc in the network connects to their server which assign an IP for it over internet. So point is to mask the second pc, and whatever it does it would be like my (first) pc is doing it so it would looks legal and second pc - hidden. For the purpouse first pc have to be configured as gateway and share its own internet connection to the second pc (and others pc if there are some). This way the connection wont be shared equal to all pcs - it would be dinamically split depends on need. You wont need any additional software aswell. I wont look at ISP-required settings for LAN and internet connection cause they are ISP specific settings. What we are interested in, is the network configuration at "the other side" - setting the home LAN. Here is a list of connections on the first pc that i gonna call Gateway (afterall, we want it to act as such)
Dont look at hamachi network that have nothing to do in this case and its just software not even using a physical network adapter. "LAN - Isi" is the network for the second pc (which i gonna call client) that we want to connect to internet and stay hidden aswell. "LAN - Sofianet" is for the ISP.
Settings for LAN - Isi or with other words - the home network we are about to set, dont really matter - they can be completely different from those for your ISP LAN settings. Still i decided to keep the same subnet mask. As for computers IPs i just chose addresses that would be easier for me to remember. As for Gateway, i set 155.55.0.1 IP for the first pc and 155.55.0.2 for the second (client). Again i remind this dotn real;ly mater as long as you remember the IPs you choosed and dont set one and the same IPs for both pcs. As gateway address set 155.55.0.1 for both pcs or with other words - the gateway address is the address of the pc that would act as gateway. For the first pc (gateway) leave DNS fields blank and for the client - set the same IP address written for gateway which in this case is 155.55.0.1. This is important cause if you leave DNS blank or enter wrong address in client settings for it, internet connection from the gateway wont be accessible. Here is how client comoputer, LAN settings looks like:
Gateway pc have the same settings except its own IP - 155.55.0.1 and DNS fields - blank.
Warning: dont not use similar IPs to those which your ISP assigns you. As example i have IP assigned from my ISP which i enter manually and it never changes - in my case 90.1.0.199. This address can be automatically obtained from the network - in such case just check your current one at the moment and use different class IP for the internal network. Here is network addresses for the gateway:
Now you only need to share the internet connection to your home network - in properties of your internet connection on the gateway you have a share option which allows you to share the connection to specific network, so you choose to share it to your home network - in this case "LAN -Isi". If you make a mistake and share the connection to your ISP LAN then alot of users will see it including your ISP so its like ring the bell to evrybody which is not a good idea
Now you have your home network set and internet - shared. However this is far from perfect. Both gateway and client are not verry "friendly" to each other and communication is limited just to the shared internet. To fix this you need to fix ICMP settings in Windows Firewall (nomatter are you using it or not). The following need to be set for both client and gateway, despite soem of them are only needed for the gateway:
Now both computers are far more comunicative - as example they can ping each other and client can trace throught the gateway:
As first hop will appier the first pc (the gateway).
Gateway also take care over the protection of client cause the gateway's firewall (in my case Windows firewall) filter the trafic. So the firewall on the client would be a bit useless (in my case - Zone Alarm) except in cases where gateway's firewall miss something.
(internet status on client)
This is what you need to do in common to share the internet and share the internet with another PC at home and keep it hidden in same time. In case there are more pcs that need to be connected and hidded and you can afford spending money for additional equipment, the intelligent way is to buy a router+switch (two in one) device - smart, flexible and simple way to build your home network and share internet. Definatly dont buy only switch cause you will expouse all pcs to your ISP network while router will represend itself as a specific computer in your ISP network and route the traffic to the right pc in your home network.
Additional problem would be the cable work - its usually hell:
(back of the gateway)
Additional power connectors are always welcomed.
(the gateway)
In case the pcs become 3 or more cables becomes even worse:
(client pc on the right and temporally 3rd pc on the left)
